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<li class="toctree-l2"><a class="reference external" href="https://web.cels.anl.gov/projects/petsc/vault/petsc-3.22/docs"> 3.22</a></li>
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  <section class="tex2jax_ignore mathjax_ignore" id="petsc-for-fortran-users">
<span id="ch-fortran"></span><h1>PETSc for Fortran Users<a class="headerlink" href="#petsc-for-fortran-users" title="Link to this heading">#</a></h1>
<p>Make sure the suffix of your Fortran files is .F90, not .f or .f90.</p>
<section id="basic-fortran-api-differences">
<h2>Basic Fortran API Differences<a class="headerlink" href="#basic-fortran-api-differences" title="Link to this heading">#</a></h2>
<section id="modules-and-include-files">
<span id="sec-fortran-includes"></span><h3>Modules and Include Files<a class="headerlink" href="#modules-and-include-files" title="Link to this heading">#</a></h3>
<p>You must use both PETSc include files and modules.
At the beginning of every function and module definition you need something like</p>
<div class="highlight-fortran notranslate"><div class="highlight"><pre><span></span><span class="cp">#include &quot;petsc/finclude/petscXXX.h&quot;</span>
<span class="w">   </span><span class="k">use </span><span class="n">petscXXX</span>
</pre></div>
</div>
<p>The Fortran include files for PETSc are located in the directory
<code class="docutils notranslate"><span class="pre">$PETSC_DIR/include/petsc/finclude</span></code> and the module files are located in <code class="docutils notranslate"><span class="pre">$PETSC_DIR/$PETSC_ARCH/include</span></code></p>
<p>The include files are nested, that is, for example, <code class="docutils notranslate"><span class="pre">petsc/finclude/petscmat.h</span></code> automatically includes
<code class="docutils notranslate"><span class="pre">petsc/finclude/petscvec.h</span></code> and so on. Except for <code class="docutils notranslate"><span class="pre">petscsys</span></code> which is nested in the other modules,
modules are <strong>not</strong> nested. Thus if your routine uses, for example, both
<code class="docutils notranslate"><span class="pre"><a href="../manualpages/Mat/Mat.html">Mat</a></span></code> and <code class="docutils notranslate"><span class="pre"><a href="../manualpages/Vec/Vec.html">Vec</a></span></code> operations you need</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">use</span><span class="w"> </span><span class="n">petscvec</span>
<span class="n">use</span><span class="w"> </span><span class="n">petscmat</span>
</pre></div>
</div>
<p>The reason they are not nested is that they are very large and including all of them slows down the compile time.
One can use</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">use</span><span class="w"> </span><span class="n">petsc</span>
</pre></div>
</div>
<p>to include all of them. In addition, if you have a routine that does not have function calls for an object, but has
the object as an argument you can use, for example,</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">subroutine</span><span class="w"> </span><span class="n">FormFunction</span><span class="p">(</span><span class="n">snes</span><span class="p">,</span><span class="n">x</span><span class="p">,</span><span class="n">f</span><span class="p">,</span><span class="n">dummy</span><span class="p">,</span><span class="n">ierr</span><span class="p">)</span>
<span class="w">  </span><span class="n">use</span><span class="w"> </span><span class="n">petscvec</span>
<span class="w">  </span><span class="n">use</span><span class="w"> </span><span class="n">petscsnesdef</span>
<span class="w">  </span><span class="n">implicit</span><span class="w"> </span><span class="n">none</span>
</pre></div>
</div>
</section>
<section id="declaring-petsc-object-variables">
<h3>Declaring PETSc Object Variables<a class="headerlink" href="#declaring-petsc-object-variables" title="Link to this heading">#</a></h3>
<p>You can declare PETSc object variables using either of the following:</p>
<div class="highlight-fortran notranslate"><div class="highlight"><pre><span></span><span class="n">XXX</span><span class="w"> </span><span class="n">variablename</span>
</pre></div>
</div>
<div class="highlight-fortran notranslate"><div class="highlight"><pre><span></span><span class="k">type</span><span class="p">(</span><span class="n">tXXX</span><span class="p">)</span><span class="w"> </span><span class="n">variablename</span>
</pre></div>
</div>
<p>For example,</p>
<div class="highlight-fortran notranslate"><div class="highlight"><pre><span></span><span class="cp">#include &quot;petsc/finclude/petscvec.h&quot;</span>
<span class="w">  </span><span class="k">use </span><span class="n">petscvec</span>

<span class="w">  </span><span class="n"><a href="../manualpages/Vec/Vec.html">Vec</a></span><span class="w"> </span><span class="n">b</span>
<span class="w">  </span><span class="k">type</span><span class="p">(</span><span class="n">tVec</span><span class="p">)</span><span class="w"> </span><span class="n">x</span>
</pre></div>
</div>
<p>PETSc types like <code class="docutils notranslate"><span class="pre"><a href="../manualpages/Sys/PetscInt.html">PetscInt</a></span></code> and <code class="docutils notranslate"><span class="pre"><a href="../manualpages/Sys/PetscReal.html">PetscReal</a></span></code> are simply aliases for basic Fortran types and cannot be written as <code class="docutils notranslate"><span class="pre">type(tPetscInt)</span></code></p>
<p>PETSc objects are always automatically initialized when declared so you do not need to (and should not) do</p>
<div class="highlight-fortran notranslate"><div class="highlight"><pre><span></span><span class="k">type</span><span class="p">(</span><span class="n">tXXX</span><span class="p">)</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">PETSC_NULL_XXX</span>
<span class="n">XXX</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">PETSC_NULL_XXX</span>
</pre></div>
</div>
</section>
<section id="calling-sequences">
<h3>Calling Sequences<a class="headerlink" href="#calling-sequences" title="Link to this heading">#</a></h3>
<p>The calling sequences for the Fortran version are in most cases
identical to the C version, except for the error checking variable
discussed in <a class="reference internal" href="#sec-fortran-errors"><span class="std std-ref">Error Checking</span></a>.</p>
<p>The key differences in handling arguments when calling PETSc functions from Fortran are</p>
<ul class="simple">
<li><p>One cannot pass a scalar variable to a function expecting an array, <a class="reference internal" href="#sec-passarray"><span class="std std-ref">Passing Arrays To PETSc Functions</span></a>.</p></li>
<li><p>One must use type specific <code class="docutils notranslate"><span class="pre">PETSC_NULL</span></code> arguments, such as <code class="docutils notranslate"><span class="pre">PETSC_NULL_INTEGER</span></code>, <a class="reference internal" href="#sec-nullptr"><span class="std std-ref">Passing null pointers to PETSc functions</span></a>.</p></li>
<li><p>One must pass pointers to arrays for arguments that output an array, for example <code class="docutils notranslate"><span class="pre"><a href="../manualpages/Sys/PetscScalar.html">PetscScalar</a>,</span> <span class="pre">pointer</span> <span class="pre">\:\:</span> <span class="pre">a(\:)</span></code>,
<a class="reference internal" href="#sec-fortranarrays"><span class="std std-ref">Output Arrays from PETSc functions</span></a>.</p></li>
<li><p><code class="docutils notranslate"><span class="pre"><a href="../manualpages/Sys/PETSC_DECIDE.html">PETSC_DECIDE</a></span></code> and friends need to match the argument type, for example <code class="docutils notranslate"><span class="pre">PETSC_DECIDE_INTEGER</span></code>.</p></li>
</ul>
<p>When passing floating point numbers into PETSc Fortran subroutines, always
make sure you have them marked as double precision (e.g., pass in <code class="docutils notranslate"><span class="pre">10.d0</span></code>
instead of <code class="docutils notranslate"><span class="pre">10.0</span></code> or declare them as PETSc variables, e.g.
<code class="docutils notranslate"><span class="pre"><a href="../manualpages/Sys/PetscScalar.html">PetscScalar</a></span> <span class="pre">one</span> <span class="pre">=</span> <span class="pre">1.0</span></code>). Otherwise, the compiler interprets the input as a single
precision number, which can cause crashes or other mysterious problems.
We <strong>highly</strong> recommend using the <code class="docutils notranslate"><span class="pre">implicit</span> <span class="pre">none</span></code>
option at the beginning of each Fortran subroutine and declaring all variables.</p>
</section>
<section id="error-checking">
<span id="sec-fortran-errors"></span><h3>Error Checking<a class="headerlink" href="#error-checking" title="Link to this heading">#</a></h3>
<p>In the Fortran version, each PETSc routine has as its final argument an
integer error variable. The error code is
nonzero if an error has been detected; otherwise, it is zero. For
example, the Fortran and C variants of <code class="docutils notranslate"><span class="pre"><a href="../manualpages/KSP/KSPSolve.html">KSPSolve</a>()</span></code> are given,
respectively, below, where <code class="docutils notranslate"><span class="pre">ierr</span></code> denotes the <code class="docutils notranslate"><span class="pre"><a href="../manualpages/Sys/PetscErrorCode.html">PetscErrorCode</a></span></code> error variable:</p>
<div class="highlight-fortran notranslate"><div class="highlight"><pre><span></span><span class="k">call </span><span class="n"><a href="../manualpages/KSP/KSPSolve.html">KSPSolve</a></span><span class="p">(</span><span class="n">ksp</span><span class="p">,</span><span class="w"> </span><span class="n">b</span><span class="p">,</span><span class="w"> </span><span class="n">x</span><span class="p">,</span><span class="w"> </span><span class="n">ierr</span><span class="p">)</span><span class="w"> </span><span class="c">! Fortran</span>
<span class="n">ierr</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n"><a href="../manualpages/KSP/KSPSolve.html">KSPSolve</a></span><span class="p">(</span><span class="n">ksp</span><span class="p">,</span><span class="w"> </span><span class="n">b</span><span class="p">,</span><span class="w"> </span><span class="n">x</span><span class="p">);</span><span class="w">    </span><span class="o">//</span><span class="w"> </span><span class="n">C</span>
</pre></div>
</div>
<p>For proper error handling one should not use the above syntax instead one should use</p>
<div class="highlight-fortran notranslate"><div class="highlight"><pre><span></span><span class="n"><a href="../manualpages/Sys/PetscCall.html">PetscCall</a></span><span class="p">(</span><span class="n"><a href="../manualpages/KSP/KSPSolve.html">KSPSolve</a></span><span class="p">(</span><span class="n">ksp</span><span class="p">,</span><span class="w"> </span><span class="n">b</span><span class="p">,</span><span class="w"> </span><span class="n">x</span><span class="p">,</span><span class="w"> </span><span class="n">ierr</span><span class="p">))</span><span class="w">   </span><span class="c">! Fortran subroutines</span>
<span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/KSP/KSPSolve.html">KSPSolve</a></span><span class="p">(</span><span class="n">ksp</span><span class="p">,</span><span class="w"> </span><span class="n">b</span><span class="p">,</span><span class="w"> </span><span class="n">x</span><span class="p">,</span><span class="w"> </span><span class="n">ierr</span><span class="p">))</span><span class="w">  </span><span class="c">! Fortran main program</span>
<span class="n"><a href="../manualpages/Sys/PetscCall.html">PetscCall</a></span><span class="p">(</span><span class="n"><a href="../manualpages/KSP/KSPSolve.html">KSPSolve</a></span><span class="p">(</span><span class="n">ksp</span><span class="p">,</span><span class="w"> </span><span class="n">b</span><span class="p">,</span><span class="w"> </span><span class="n">x</span><span class="p">))</span><span class="w">         </span><span class="o">//</span><span class="w"> </span><span class="n">C</span>
</pre></div>
</div>
</section>
<section id="passing-arrays-to-petsc-functions">
<span id="sec-passarray"></span><h3>Passing Arrays To PETSc Functions<a class="headerlink" href="#passing-arrays-to-petsc-functions" title="Link to this heading">#</a></h3>
<p>Many PETSc functions take arrays as arguments; in Fortran they must be passed as arrays even if the “array”
is of length one (unlike Fortran 77 where one can pass scalars to functions expecting arrays). When passing
a single value one can use the Fortran [] notation to pass the scalar as an array, for example</p>
<div class="highlight-fortran notranslate"><div class="highlight"><pre><span></span><span class="n"><a href="../manualpages/Sys/PetscCall.html">PetscCall</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecSetValues.html">VecSetValues</a></span><span class="p">(</span><span class="n">v</span><span class="p">,</span><span class="w"> </span><span class="n">one</span><span class="p">,</span><span class="w"> </span><span class="p">[</span><span class="n">i</span><span class="p">],</span><span class="w"> </span><span class="p">[</span><span class="n">val</span><span class="p">],</span><span class="w"> </span><span class="n">ierr</span><span class="p">))</span>
</pre></div>
</div>
<p>This trick can only be used for arrays used to pass data into a PETSc routine, it cannot be used
for arrays used to receive data from a PETSc routine. For example,</p>
<div class="highlight-fortran notranslate"><div class="highlight"><pre><span></span><span class="n"><a href="../manualpages/Sys/PetscCall.html">PetscCall</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecGetValues.html">VecGetValues</a></span><span class="p">(</span><span class="n">v</span><span class="p">,</span><span class="w"> </span><span class="n">one</span><span class="p">,</span><span class="w"> </span><span class="n">idx</span><span class="p">,</span><span class="w"> </span><span class="p">[</span><span class="n">val</span><span class="p">],</span><span class="w"> </span><span class="n">ierr</span><span class="p">))</span>
</pre></div>
</div>
<p>is invalid and will not set <code class="docutils notranslate"><span class="pre">val</span></code> with the correct value.</p>
</section>
<section id="passing-null-pointers-to-petsc-functions">
<span id="sec-nullptr"></span><h3>Passing null pointers to PETSc functions<a class="headerlink" href="#passing-null-pointers-to-petsc-functions" title="Link to this heading">#</a></h3>
<p>Many PETSc C functions have the option of passing a <code class="docutils notranslate"><span class="pre">NULL</span></code>
argument (for example, the fifth argument of <code class="docutils notranslate"><span class="pre"><a href="../manualpages/Mat/MatCreateSeqAIJ.html">MatCreateSeqAIJ</a>()</span></code>).
From Fortran, users <em>must</em> pass <code class="docutils notranslate"><span class="pre">PETSC_NULL_XXX</span></code> to indicate a null
argument (where <code class="docutils notranslate"><span class="pre">XXX</span></code> is <code class="docutils notranslate"><span class="pre">INTEGER</span></code>, <code class="docutils notranslate"><span class="pre">DOUBLE</span></code>, <code class="docutils notranslate"><span class="pre">CHARACTER</span></code>,
<code class="docutils notranslate"><span class="pre">SCALAR</span></code>, <code class="docutils notranslate"><span class="pre">VEC</span></code>, <code class="docutils notranslate"><span class="pre">MAT</span></code>, etc depending on the argument type). For example, when no options prefix is desired
in the routine <code class="docutils notranslate"><span class="pre"><a href="../manualpages/Sys/PetscOptionsGetInt.html">PetscOptionsGetInt</a>()</span></code>, one must use the following
command in Fortran:</p>
<div class="highlight-fortran notranslate"><div class="highlight"><pre><span></span><span class="n"><a href="../manualpages/Sys/PetscCall.html">PetscCall</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Sys/PetscOptionsGetInt.html">PetscOptionsGetInt</a></span><span class="p">(</span><span class="n">PETSC_NULL_OPTIONS</span><span class="p">,</span><span class="w"> </span><span class="n">PETSC_NULL_CHARACTER</span><span class="p">,</span><span class="w"> </span><span class="n">PETSC_NULL_CHARACTER</span><span class="p">,</span><span class="w"> </span><span class="s1">&#39;-name&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">flg</span><span class="p">,</span><span class="w"> </span><span class="n">ierr</span><span class="p">))</span>
</pre></div>
</div>
<p>Where the code expects an array, then use <code class="docutils notranslate"><span class="pre">PETSC_NULL_XXX_ARRAY</span></code>. For example:</p>
<div class="highlight-fortran notranslate"><div class="highlight"><pre><span></span><span class="n"><a href="../manualpages/Sys/PetscCall.html">PetscCall</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Mat/MatCreateSeqDense.html">MatCreateSeqDense</a></span><span class="p">(</span><span class="n">comm</span><span class="p">,</span><span class="w"> </span><span class="n">m</span><span class="p">,</span><span class="w"> </span><span class="n">n</span><span class="p">,</span><span class="w"> </span><span class="n">PETSC_NULL_SCALAR_ARRAY</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p">))</span>
</pre></div>
</div>
<p>When a PETSc function returns multiple arrays, such as <code class="docutils notranslate"><span class="pre"><a href="../manualpages/DMDA/DMDAGetOwnershipRanges.html">DMDAGetOwnershipRanges</a>()</span></code> and the user does not need
certain arrays they must pass <code class="docutils notranslate"><span class="pre">PETSC_NULL_XXX_POINTER</span></code> as the argument. For example,</p>
<div class="highlight-fortran notranslate"><div class="highlight"><pre><span></span><span class="n"><a href="../manualpages/Sys/PetscInt.html">PetscInt</a></span><span class="p">,</span><span class="w"> </span><span class="k">pointer</span><span class="w"> </span><span class="kd">::</span><span class="w"> </span><span class="n">lx</span><span class="p">(:),</span><span class="w"> </span><span class="n">ly</span><span class="p">(:)</span>
<span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/DMDA/DMDAGetOwnershipRanges.html">DMDAGetOwnershipRanges</a></span><span class="p">(</span><span class="n">da</span><span class="p">,</span><span class="w"> </span><span class="n">lx</span><span class="p">,</span><span class="w"> </span><span class="n">ly</span><span class="p">,</span><span class="w"> </span><span class="n">PETSC_NULL_INTEGER_POINTER</span><span class="p">,</span><span class="w"> </span><span class="n">ierr</span><span class="p">))</span>
<span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n">DMDARestoreOwnershipRanges</span><span class="p">(</span><span class="n">da</span><span class="p">,</span><span class="w"> </span><span class="n">lx</span><span class="p">,</span><span class="w"> </span><span class="n">ly</span><span class="p">,</span><span class="w"> </span><span class="n">PETSC_NULL_INTEGER_POINTER</span><span class="p">,</span><span class="w"> </span><span class="n">ierr</span><span class="p">))</span>
</pre></div>
</div>
<p>Arguments that are fully defined Fortran derived types (C structs), such as <code class="docutils notranslate"><span class="pre"><a href="../manualpages/Mat/MatFactorInfo.html">MatFactorInfo</a></span></code> or <code class="docutils notranslate"><span class="pre"><a href="../manualpages/PetscSF/PetscSFNode.html">PetscSFNode</a></span></code>,
cannot be passed as null from Fortran. A properly defined variable must be passed in for those arguments.</p>
<p>Finally when a subroutine returns a <code class="docutils notranslate"><span class="pre"><a href="../manualpages/Sys/PetscObject.html">PetscObject</a></span></code> through an argument, to check if it is <code class="docutils notranslate"><span class="pre">NULL</span></code> you must use:</p>
<div class="highlight-fortran notranslate"><div class="highlight"><pre><span></span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n"><a href="../manualpages/Sys/PetscObjectIsNull.html">PetscObjectIsNull</a></span><span class="p">(</span><span class="n">dm</span><span class="p">))</span><span class="w"> </span><span class="k">then</span>
<span class="k">if</span><span class="w"> </span><span class="p">(.</span><span class="nb">not</span><span class="p">.</span><span class="w"> </span><span class="n"><a href="../manualpages/Sys/PetscObjectIsNull.html">PetscObjectIsNull</a></span><span class="p">(</span><span class="n">dm</span><span class="p">))</span><span class="w"> </span><span class="k">then</span>
</pre></div>
</div>
<p>you cannot use</p>
<div class="highlight-fortran notranslate"><div class="highlight"><pre><span></span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">dm</span><span class="w"> </span><span class="p">.</span><span class="n">eq</span><span class="p">.</span><span class="w"> </span><span class="n">PETSC_NULL_DM</span><span class="p">)</span><span class="w"> </span><span class="k">then</span>
</pre></div>
</div>
<p>Note that</p>
<div class="highlight-fortran notranslate"><div class="highlight"><pre><span></span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n"><a href="../manualpages/Sys/PetscObjectIsNull.html">PetscObjectIsNull</a></span><span class="p">(</span><span class="n">PETSC_NULL_VEC</span><span class="p">))</span><span class="w"> </span><span class="k">then</span>
</pre></div>
</div>
<p>will always return true, for any PETSc object.</p>
<p>These specializations with <code class="docutils notranslate"><span class="pre">NULL</span></code> types are required because of Fortran’s strict type checking system and lack of a concept of <code class="docutils notranslate"><span class="pre">NULL</span></code>,
the Fortran compiler will often warn you if the wrong <code class="docutils notranslate"><span class="pre">NULL</span></code> type is passed.</p>
</section>
<section id="output-arrays-from-petsc-functions">
<span id="sec-fortranarrays"></span><h3>Output Arrays from PETSc functions<a class="headerlink" href="#output-arrays-from-petsc-functions" title="Link to this heading">#</a></h3>
<p>For PETSc routine arguments that return an array of <code class="docutils notranslate"><span class="pre"><a href="../manualpages/Sys/PetscInt.html">PetscInt</a></span></code>, <code class="docutils notranslate"><span class="pre"><a href="../manualpages/Sys/PetscScalar.html">PetscScalar</a></span></code>, <code class="docutils notranslate"><span class="pre"><a href="../manualpages/Sys/PetscReal.html">PetscReal</a></span></code> or of PETSc objects,
one passes in a pointer to an array and the PETSc routine returns an array containing the values. For example,</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n"><a href="../manualpages/Sys/PetscScalar.html">PetscScalar</a></span><span class="w"> </span><span class="o">*</span><span class="n">a</span><span class="p">;</span>
<span class="n"><a href="../manualpages/Vec/Vec.html">Vec</a></span><span class="w">         </span><span class="n">v</span><span class="p">;</span>
<span class="n"><a href="../manualpages/Vec/VecGetArray.html">VecGetArray</a></span><span class="p">(</span><span class="n">v</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">a</span><span class="p">);</span>
</pre></div>
</div>
<p>is in Fortran,</p>
<div class="highlight-fortran notranslate"><div class="highlight"><pre><span></span><span class="n"><a href="../manualpages/Sys/PetscScalar.html">PetscScalar</a></span><span class="p">,</span><span class="w"> </span><span class="k">pointer</span><span class="w"> </span><span class="kd">::</span><span class="w"> </span><span class="n">a</span><span class="p">(:)</span>
<span class="n"><a href="../manualpages/Vec/Vec.html">Vec</a></span><span class="p">,</span><span class="w">         </span><span class="n">v</span>
<span class="n"><a href="../manualpages/Vec/VecGetArray.html">VecGetArray</a></span><span class="p">(</span><span class="n">v</span><span class="p">,</span><span class="w"> </span><span class="n">a</span><span class="p">,</span><span class="w"> </span><span class="n">ierr</span><span class="p">)</span>
</pre></div>
</div>
<p>For PETSc routine arguments that return a character string (array), e.g. <code class="docutils notranslate"><span class="pre">const</span> <span class="pre">char</span> <span class="pre">*str[]</span></code> pass a string long enough to hold the
result. For example,</p>
<div class="highlight-fortran notranslate"><div class="highlight"><pre><span></span><span class="kt">character</span><span class="o">*</span><span class="p">(</span><span class="mi">80</span><span class="p">)</span><span class="w">  </span><span class="n">str</span>
<span class="n"><a href="../manualpages/Sys/PetscCall.html">PetscCall</a></span><span class="p">(</span><span class="n"><a href="../manualpages/KSP/KSPGetType.html">KSPGetType</a></span><span class="p">(</span><span class="n">ksp</span><span class="p">,</span><span class="n">str</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
</pre></div>
</div>
<p>The result is copied into <code class="docutils notranslate"><span class="pre">str</span></code>.</p>
<p>Similarly, for PETSc routines where the user provides a character array (to be filled) followed by the array’s length, e.g. <code class="docutils notranslate"><span class="pre">char</span> <span class="pre">name[],</span> <span class="pre">size_t</span> <span class="pre">nlen</span></code>.
In Fortran pass a string long enough to hold the result, but not the separate length argument. For example,</p>
<div class="highlight-fortran notranslate"><div class="highlight"><pre><span></span><span class="kt">character</span><span class="o">*</span><span class="p">(</span><span class="mi">80</span><span class="p">)</span><span class="w">  </span><span class="n">str</span>
<span class="n"><a href="../manualpages/Sys/PetscCall.html">PetscCall</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Sys/PetscGetHostName.html">PetscGetHostName</a></span><span class="p">(</span><span class="n">name</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
</pre></div>
</div>
</section>
<section id="matrix-vector-and-is-indices">
<h3>Matrix, Vector and IS Indices<a class="headerlink" href="#matrix-vector-and-is-indices" title="Link to this heading">#</a></h3>
<p>All matrices, vectors and <code class="docutils notranslate"><span class="pre"><a href="../manualpages/IS/IS.html">IS</a></span></code> in PETSc use zero-based indexing in the PETSc API
regardless of whether C or Fortran is being used. For example,
<code class="docutils notranslate"><span class="pre"><a href="../manualpages/Mat/MatSetValues.html">MatSetValues</a>()</span></code> and <code class="docutils notranslate"><span class="pre"><a href="../manualpages/Vec/VecSetValues.html">VecSetValues</a>()</span></code> always use
zero indexing. See <a class="reference internal" href="mat.html#sec-matoptions"><span class="std std-ref">Basic Matrix Operations</span></a> for further
details.</p>
<p>Indexing into Fortran arrays, for example obtained with <code class="docutils notranslate"><span class="pre"><a href="../manualpages/Vec/VecGetArray.html">VecGetArray</a>()</span></code>, uses the Fortran
convention and generally begin with 1 except for special routines such as <code class="docutils notranslate"><span class="pre"><a href="../manualpages/DMDA/DMDAVecGetArray.html">DMDAVecGetArray</a>()</span></code> which uses the ranges
provided by <code class="docutils notranslate"><span class="pre"><a href="../manualpages/DMDA/DMDAGetCorners.html">DMDAGetCorners</a>()</span></code>.</p>
</section>
<section id="setting-routines-and-contexts">
<h3>Setting Routines and Contexts<a class="headerlink" href="#setting-routines-and-contexts" title="Link to this heading">#</a></h3>
<p>Some PETSc functions take as arguments user-functions and contexts for the function. For example</p>
<div class="highlight-fortran notranslate"><div class="highlight"><pre><span></span><span class="k">external </span><span class="n">func</span>
<span class="n"><a href="../manualpages/SNES/SNESSetFunction.html">SNESSetFunction</a></span><span class="p">(</span><span class="n">snes</span><span class="p">,</span><span class="w"> </span><span class="n">r</span><span class="p">,</span><span class="w"> </span><span class="n">func</span><span class="p">,</span><span class="w"> </span><span class="n">ctx</span><span class="p">,</span><span class="w"> </span><span class="n">ierr</span><span class="p">)</span>
<span class="n"><a href="../manualpages/SNES/SNES.html">SNES</a></span><span class="w"> </span><span class="n">snes</span>
<span class="n"><a href="../manualpages/Vec/Vec.html">Vec</a></span><span class="w"> </span><span class="n">r</span>
<span class="n"><a href="../manualpages/Sys/PetscErrorCode.html">PetscErrorCode</a></span><span class="w"> </span><span class="n">ierr</span>
</pre></div>
</div>
<p>where <code class="docutils notranslate"><span class="pre">func</span></code> has the calling sequence</p>
<div class="highlight-fortran notranslate"><div class="highlight"><pre><span></span><span class="k">subroutine </span><span class="n">func</span><span class="p">(</span><span class="n">snes</span><span class="p">,</span><span class="w"> </span><span class="n">x</span><span class="p">,</span><span class="w"> </span><span class="n">f</span><span class="p">,</span><span class="w"> </span><span class="n">ctx</span><span class="p">,</span><span class="w"> </span><span class="n">ierr</span><span class="p">)</span>
<span class="n"><a href="../manualpages/SNES/SNES.html">SNES</a></span><span class="w"> </span><span class="n">snes</span>
<span class="n"><a href="../manualpages/Vec/Vec.html">Vec</a></span><span class="w"> </span><span class="n">x</span><span class="p">,</span><span class="n">f</span>
<span class="n"><a href="../manualpages/Sys/PetscErrorCode.html">PetscErrorCode</a></span><span class="w"> </span><span class="n">ierr</span>
</pre></div>
</div>
<p>and <code class="docutils notranslate"><span class="pre">ctx</span></code> can be almost anything (represented as <code class="docutils notranslate"><span class="pre">void</span> <span class="pre">*</span></code> in C).</p>
<p>It can be a Fortran derived type as in</p>
<div class="highlight-fortran notranslate"><div class="highlight"><pre><span></span><span class="k">subroutine </span><span class="n">func</span><span class="p">(</span><span class="n">snes</span><span class="p">,</span><span class="w"> </span><span class="n">x</span><span class="p">,</span><span class="w"> </span><span class="n">f</span><span class="p">,</span><span class="w"> </span><span class="n">ctx</span><span class="p">,</span><span class="w"> </span><span class="n">ierr</span><span class="p">)</span>
<span class="n"><a href="../manualpages/SNES/SNES.html">SNES</a></span><span class="w"> </span><span class="n">snes</span>
<span class="n"><a href="../manualpages/Vec/Vec.html">Vec</a></span><span class="w"> </span><span class="n">x</span><span class="p">,</span><span class="n">f</span>
<span class="k">type</span><span class="w"> </span><span class="p">(</span><span class="n">userctx</span><span class="p">)</span><span class="w">   </span><span class="n">ctx</span>
<span class="n"><a href="../manualpages/Sys/PetscErrorCode.html">PetscErrorCode</a></span><span class="w"> </span><span class="n">ierr</span>
<span class="p">...</span>

<span class="k">external </span><span class="n">func</span>
<span class="n"><a href="../manualpages/SNES/SNESSetFunction.html">SNESSetFunction</a></span><span class="p">(</span><span class="n">snes</span><span class="p">,</span><span class="w"> </span><span class="n">r</span><span class="p">,</span><span class="w"> </span><span class="n">func</span><span class="p">,</span><span class="w"> </span><span class="n">ctx</span><span class="p">,</span><span class="w"> </span><span class="n">ierr</span><span class="p">)</span>
<span class="n"><a href="../manualpages/SNES/SNES.html">SNES</a></span><span class="w"> </span><span class="n">snes</span>
<span class="n"><a href="../manualpages/Vec/Vec.html">Vec</a></span><span class="w"> </span><span class="n">r</span>
<span class="n"><a href="../manualpages/Sys/PetscErrorCode.html">PetscErrorCode</a></span><span class="w"> </span><span class="n">ierr</span>
<span class="k">type</span><span class="w"> </span><span class="p">(</span><span class="n">userctx</span><span class="p">)</span><span class="w">   </span><span class="n">ctx</span>
</pre></div>
</div>
<p>or a PETSc object</p>
<div class="highlight-fortran notranslate"><div class="highlight"><pre><span></span><span class="k">subroutine </span><span class="n">func</span><span class="p">(</span><span class="n">snes</span><span class="p">,</span><span class="w"> </span><span class="n">x</span><span class="p">,</span><span class="w"> </span><span class="n">f</span><span class="p">,</span><span class="w"> </span><span class="n">ctx</span><span class="p">,</span><span class="w"> </span><span class="n">ierr</span><span class="p">)</span>
<span class="n"><a href="../manualpages/SNES/SNES.html">SNES</a></span><span class="w"> </span><span class="n">snes</span>
<span class="n"><a href="../manualpages/Vec/Vec.html">Vec</a></span><span class="w"> </span><span class="n">x</span><span class="p">,</span><span class="n">f</span>
<span class="n"><a href="../manualpages/Vec/Vec.html">Vec</a></span><span class="w"> </span><span class="n">ctx</span>
<span class="n"><a href="../manualpages/Sys/PetscErrorCode.html">PetscErrorCode</a></span><span class="w"> </span><span class="n">ierr</span>
<span class="p">...</span>

<span class="k">external </span><span class="n">func</span>
<span class="n"><a href="../manualpages/SNES/SNESSetFunction.html">SNESSetFunction</a></span><span class="p">(</span><span class="n">snes</span><span class="p">,</span><span class="w"> </span><span class="n">r</span><span class="p">,</span><span class="w"> </span><span class="n">func</span><span class="p">,</span><span class="w"> </span><span class="n">ctx</span><span class="p">,</span><span class="w"> </span><span class="n">ierr</span><span class="p">)</span>
<span class="n"><a href="../manualpages/SNES/SNES.html">SNES</a></span><span class="w"> </span><span class="n">snes</span>
<span class="n"><a href="../manualpages/Vec/Vec.html">Vec</a></span><span class="w"> </span><span class="n">r</span>
<span class="n"><a href="../manualpages/Sys/PetscErrorCode.html">PetscErrorCode</a></span><span class="w"> </span><span class="n">ierr</span>
<span class="n"><a href="../manualpages/Vec/Vec.html">Vec</a></span><span class="w"> </span><span class="n">ctx</span>
</pre></div>
</div>
<p>or nothing</p>
<div class="highlight-fortran notranslate"><div class="highlight"><pre><span></span><span class="k">subroutine </span><span class="n">func</span><span class="p">(</span><span class="n">snes</span><span class="p">,</span><span class="w"> </span><span class="n">x</span><span class="p">,</span><span class="w"> </span><span class="n">f</span><span class="p">,</span><span class="w"> </span><span class="n">dummy</span><span class="p">,</span><span class="w"> </span><span class="n">ierr</span><span class="p">)</span>
<span class="n"><a href="../manualpages/SNES/SNES.html">SNES</a></span><span class="w"> </span><span class="n">snes</span>
<span class="n"><a href="../manualpages/Vec/Vec.html">Vec</a></span><span class="w"> </span><span class="n">x</span><span class="p">,</span><span class="n">f</span>
<span class="kt">integer </span><span class="n">dummy</span><span class="p">(</span><span class="o">*</span><span class="p">)</span>
<span class="n"><a href="../manualpages/Sys/PetscErrorCode.html">PetscErrorCode</a></span><span class="w"> </span><span class="n">ierr</span>
<span class="p">...</span>

<span class="k">external </span><span class="n">func</span>
<span class="n"><a href="../manualpages/SNES/SNESSetFunction.html">SNESSetFunction</a></span><span class="p">(</span><span class="n">snes</span><span class="p">,</span><span class="w"> </span><span class="n">r</span><span class="p">,</span><span class="w"> </span><span class="n">func</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">ierr</span><span class="p">)</span>
<span class="n"><a href="../manualpages/SNES/SNES.html">SNES</a></span><span class="w"> </span><span class="n">snes</span>
<span class="n"><a href="../manualpages/Vec/Vec.html">Vec</a></span><span class="w"> </span><span class="n">r</span>
<span class="n"><a href="../manualpages/Sys/PetscErrorCode.html">PetscErrorCode</a></span><span class="w"> </span><span class="n">ierr</span>
</pre></div>
</div>
<p>When a function pointer (declared as external in Fortran) is passed as an argument to a PETSc function,
it is assumed that this
function references a routine written in the same language as the PETSc
interface function that was called. For instance, if
<code class="docutils notranslate"><span class="pre"><a href="../manualpages/SNES/SNESSetFunction.html">SNESSetFunction</a>()</span></code> is called from C, the function must be a C function. Likewise, if it is called from Fortran, the
function must be (a subroutine) written in Fortran.</p>
<p>If you are using Fortran classes that have bound functions (methods) as in
<a href="../src/snes/tests/ex18f90.F90.html">src/snes/tests/ex18f90.F90</a>, the context cannot be passed
to function pointer setting routines, such as <code class="docutils notranslate"><span class="pre"><a href="../manualpages/SNES/SNESSetFunction.html">SNESSetFunction</a>()</span></code>. Instead, one must use <code class="docutils notranslate"><span class="pre">SNESSetFunctionNoInterface()</span></code>,
and define the interface directly in the user code, see
<a href="../src/snes/tests/ex18f90.F90.html">ex18f90.F90</a>
for a full demonstration.</p>
</section>
<section id="compiling-and-linking-fortran-programs">
<span id="sec-fortcompile"></span><h3>Compiling and Linking Fortran Programs<a class="headerlink" href="#compiling-and-linking-fortran-programs" title="Link to this heading">#</a></h3>
<p>See <a class="reference internal" href="getting_started.html#sec-writing-application-codes"><span class="std std-ref">Writing C/C++ or Fortran Applications</span></a>.</p>
</section>
<section id="duplicating-multiple-vectors">
<h3>Duplicating Multiple Vectors<a class="headerlink" href="#duplicating-multiple-vectors" title="Link to this heading">#</a></h3>
<p>The Fortran interface to <code class="docutils notranslate"><span class="pre"><a href="../manualpages/Vec/VecDuplicateVecs.html">VecDuplicateVecs</a>()</span></code> differs slightly from
the C/C++ variant. To create <code class="docutils notranslate"><span class="pre">n</span></code> vectors of the same
format as an existing vector, the user must declare a vector array,
<code class="docutils notranslate"><span class="pre">v_new</span></code> of size <code class="docutils notranslate"><span class="pre">n</span></code>. Then, after <code class="docutils notranslate"><span class="pre"><a href="../manualpages/Vec/VecDuplicateVecs.html">VecDuplicateVecs</a>()</span></code> has been
called, <code class="docutils notranslate"><span class="pre">v_new</span></code> will contain (pointers to) the new PETSc vector
objects. When finished with the vectors, the user should destroy them by
calling <code class="docutils notranslate"><span class="pre"><a href="../manualpages/Vec/VecDestroyVecs.html">VecDestroyVecs</a>()</span></code>. For example, the following code fragment
duplicates <code class="docutils notranslate"><span class="pre">v_old</span></code> to form two new vectors, <code class="docutils notranslate"><span class="pre">v_new(1)</span></code> and
<code class="docutils notranslate"><span class="pre">v_new(2)</span></code>.</p>
<div class="highlight-fortran notranslate"><div class="highlight"><pre><span></span><span class="n"><a href="../manualpages/Vec/Vec.html">Vec</a></span><span class="w">          </span><span class="n">v_old</span><span class="p">,</span><span class="w"> </span><span class="n">v_new</span><span class="p">(</span><span class="mi">2</span><span class="p">)</span>
<span class="n"><a href="../manualpages/Sys/PetscInt.html">PetscInt</a></span><span class="w">     </span><span class="n">ierr</span>
<span class="n"><a href="../manualpages/Sys/PetscScalar.html">PetscScalar</a></span><span class="w">  </span><span class="n">alpha</span>
<span class="p">....</span>
<span class="n"><a href="../manualpages/Sys/PetscCall.html">PetscCall</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecDuplicateVecs.html">VecDuplicateVecs</a></span><span class="p">(</span><span class="n">v_old</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">v_new</span><span class="p">,</span><span class="w"> </span><span class="n">ierr</span><span class="p">))</span>
<span class="n">alpha</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mf">4.3</span>
<span class="n"><a href="../manualpages/Sys/PetscCall.html">PetscCall</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecSet.html">VecSet</a></span><span class="p">(</span><span class="n">v_new</span><span class="p">(</span><span class="mi">1</span><span class="p">),</span><span class="w"> </span><span class="n">alpha</span><span class="p">,</span><span class="w"> </span><span class="n">ierr</span><span class="p">))</span>
<span class="n">alpha</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mf">6.0</span>
<span class="n"><a href="../manualpages/Sys/PetscCall.html">PetscCall</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecSet.html">VecSet</a></span><span class="p">(</span><span class="n">v_new</span><span class="p">(</span><span class="mi">2</span><span class="p">),</span><span class="w"> </span><span class="n">alpha</span><span class="p">,</span><span class="w"> </span><span class="n">ierr</span><span class="p">))</span>
<span class="p">....</span>
<span class="n"><a href="../manualpages/Sys/PetscCall.html">PetscCall</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecDestroyVecs.html">VecDestroyVecs</a></span><span class="p">(</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">v_new</span><span class="p">,</span><span class="w"> </span><span class="n">ierr</span><span class="p">))</span>
</pre></div>
</div>
</section>
</section>
<section id="sample-fortran-programs">
<span id="sec-fortran-examples"></span><h2>Sample Fortran Programs<a class="headerlink" href="#sample-fortran-programs" title="Link to this heading">#</a></h2>
<p>Sample programs that illustrate the PETSc interface for Fortran are
given below, corresponding to
<a href="../src/vec/vec/tests/ex19f.F90.html">Vec Test ex19f</a>,
<a href="../src/vec/vec/tutorials/ex4f.F90.html">Vec Tutorial ex4f</a>,
<a href="../src/sys/classes/draw/tests/ex5f.F90.html">Draw Test ex5f</a>,
and
<a href="../src/snes/tutorials/ex1f.F90.html">SNES Tutorial ex1f</a>,
respectively. We also refer Fortran programmers to the C examples listed
throughout the manual, since PETSc usage within the two languages
differs only slightly.</p>
<div class="admonition-listing-src-vec-vec-tests-ex19f-f90 admonition" id="vec-test-ex19f">
<p class="admonition-title">Listing: <code class="docutils notranslate"><span class="pre">src/vec/vec/tests/ex19f.F90</span></code></p>
<div class="highlight-fortran notranslate"><div class="highlight"><pre><span></span><span class="c">!</span>
<span class="c">!</span>
<span class="w">      </span><span class="k">program </span><span class="n">main</span>
<span class="cp">#include &lt;petsc/finclude/petscvec.h&gt;</span>
<span class="w">      </span><span class="k">use </span><span class="n">petscvec</span>
<span class="w">      </span><span class="k">implicit none</span>
<span class="c">!</span>
<span class="c">!  This example demonstrates basic use of the PETSc Fortran interface</span>
<span class="c">!  to vectors.</span>
<span class="c">!</span>
<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscInt.html">PetscInt</a></span><span class="w">  </span><span class="n">n</span>
<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscErrorCode.html">PetscErrorCode</a></span><span class="w"> </span><span class="n">ierr</span>
<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscBool.html">PetscBool</a></span><span class="w">  </span><span class="n">flg</span>
<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscScalar.html">PetscScalar</a></span><span class="w">      </span><span class="n">one</span><span class="p">,</span><span class="n">two</span><span class="p">,</span><span class="n">three</span><span class="p">,</span><span class="n">dot</span>
<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscReal.html">PetscReal</a></span><span class="w">        </span><span class="n">norm</span><span class="p">,</span><span class="n">rdot</span>
<span class="w">       </span><span class="n"><a href="../manualpages/Vec/Vec.html">Vec</a></span><span class="w">              </span><span class="n">x</span><span class="p">,</span><span class="n">y</span><span class="p">,</span><span class="n">w</span>
<span class="w">       </span><span class="n">PetscOptions</span><span class="w">     </span><span class="k">options</span>

<span class="k">       </span><span class="n">n</span><span class="w">     </span><span class="o">=</span><span class="w"> </span><span class="mi">20</span>
<span class="w">       </span><span class="n">one</span><span class="w">   </span><span class="o">=</span><span class="w"> </span><span class="mf">1.0</span>
<span class="w">       </span><span class="n">two</span><span class="w">   </span><span class="o">=</span><span class="w"> </span><span class="mf">2.0</span>
<span class="w">       </span><span class="n">three</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mf">3.0</span>

<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Sys/PetscInitialize.html">PetscInitialize</a></span><span class="p">(</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Sys/PetscOptionsCreate.html">PetscOptionsCreate</a></span><span class="p">(</span><span class="k">options</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Sys/PetscOptionsGetInt.html">PetscOptionsGetInt</a></span><span class="p">(</span><span class="k">options</span><span class="p">,</span><span class="n">PETSC_NULL_CHARACTER</span><span class="p">,</span><span class="s1">&#39;-n&#39;</span><span class="p">,</span><span class="n">n</span><span class="p">,</span><span class="n">flg</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Sys/PetscOptionsDestroy.html">PetscOptionsDestroy</a></span><span class="p">(</span><span class="k">options</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>

<span class="c">! Create a vector, then duplicate it</span>
<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecCreate.html">VecCreate</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Sys/PETSC_COMM_WORLD.html">PETSC_COMM_WORLD</a></span><span class="p">,</span><span class="n">x</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecSetSizes.html">VecSetSizes</a></span><span class="p">(</span><span class="n">x</span><span class="p">,</span><span class="n"><a href="../manualpages/Sys/PETSC_DECIDE.html">PETSC_DECIDE</a></span><span class="p">,</span><span class="n">n</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecSetFromOptions.html">VecSetFromOptions</a></span><span class="p">(</span><span class="n">x</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecDuplicate.html">VecDuplicate</a></span><span class="p">(</span><span class="n">x</span><span class="p">,</span><span class="n">y</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecDuplicate.html">VecDuplicate</a></span><span class="p">(</span><span class="n">x</span><span class="p">,</span><span class="n">w</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>

<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecSet.html">VecSet</a></span><span class="p">(</span><span class="n">x</span><span class="p">,</span><span class="n">one</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecSet.html">VecSet</a></span><span class="p">(</span><span class="n">y</span><span class="p">,</span><span class="n">two</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>

<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecDot.html">VecDot</a></span><span class="p">(</span><span class="n">x</span><span class="p">,</span><span class="n">y</span><span class="p">,</span><span class="n">dot</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">       </span><span class="n">rdot</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n"><a href="../manualpages/Sys/PetscRealPart.html">PetscRealPart</a></span><span class="p">(</span><span class="n">dot</span><span class="p">)</span>
<span class="w">       </span><span class="k">write</span><span class="p">(</span><span class="mi">6</span><span class="p">,</span><span class="mi">100</span><span class="p">)</span><span class="w"> </span><span class="n">rdot</span>
<span class="w">  </span><span class="mi">100</span><span class="w">  </span><span class="k">format</span><span class="p">(</span><span class="s1">&#39;Result of inner product &#39;</span><span class="p">,</span><span class="n">f10</span><span class="p">.</span><span class="mi">4</span><span class="p">)</span>

<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecScale.html">VecScale</a></span><span class="p">(</span><span class="n">x</span><span class="p">,</span><span class="n">two</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecNorm.html">VecNorm</a></span><span class="p">(</span><span class="n">x</span><span class="p">,</span><span class="n"><a href="../manualpages/Vec/NORM_2.html">NORM_2</a></span><span class="p">,</span><span class="n">norm</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">       </span><span class="k">write</span><span class="p">(</span><span class="mi">6</span><span class="p">,</span><span class="mi">110</span><span class="p">)</span><span class="w"> </span><span class="n">norm</span>
<span class="w">  </span><span class="mi">110</span><span class="w">  </span><span class="k">format</span><span class="p">(</span><span class="s1">&#39;Result of scaling &#39;</span><span class="p">,</span><span class="n">f10</span><span class="p">.</span><span class="mi">4</span><span class="p">)</span>

<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecCopy.html">VecCopy</a></span><span class="p">(</span><span class="n">x</span><span class="p">,</span><span class="n">w</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecNorm.html">VecNorm</a></span><span class="p">(</span><span class="n">w</span><span class="p">,</span><span class="n"><a href="../manualpages/Vec/NORM_2.html">NORM_2</a></span><span class="p">,</span><span class="n">norm</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">       </span><span class="k">write</span><span class="p">(</span><span class="mi">6</span><span class="p">,</span><span class="mi">120</span><span class="p">)</span><span class="w"> </span><span class="n">norm</span>
<span class="w">  </span><span class="mi">120</span><span class="w">  </span><span class="k">format</span><span class="p">(</span><span class="s1">&#39;Result of copy &#39;</span><span class="p">,</span><span class="n">f10</span><span class="p">.</span><span class="mi">4</span><span class="p">)</span>

<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecAXPY.html">VecAXPY</a></span><span class="p">(</span><span class="n">y</span><span class="p">,</span><span class="n">three</span><span class="p">,</span><span class="n">x</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecNorm.html">VecNorm</a></span><span class="p">(</span><span class="n">y</span><span class="p">,</span><span class="n"><a href="../manualpages/Vec/NORM_2.html">NORM_2</a></span><span class="p">,</span><span class="n">norm</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">       </span><span class="k">write</span><span class="p">(</span><span class="mi">6</span><span class="p">,</span><span class="mi">130</span><span class="p">)</span><span class="w"> </span><span class="n">norm</span>
<span class="w">  </span><span class="mi">130</span><span class="w">  </span><span class="k">format</span><span class="p">(</span><span class="s1">&#39;Result of axpy &#39;</span><span class="p">,</span><span class="n">f10</span><span class="p">.</span><span class="mi">4</span><span class="p">)</span>

<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecDestroy.html">VecDestroy</a></span><span class="p">(</span><span class="n">x</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecDestroy.html">VecDestroy</a></span><span class="p">(</span><span class="n">y</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecDestroy.html">VecDestroy</a></span><span class="p">(</span><span class="n">w</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Sys/PetscFinalize.html">PetscFinalize</a></span><span class="p">(</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">       </span><span class="k">end</span>
</pre></div>
</div>
</div>
<div class="admonition-listing-src-vec-vec-tutorials-ex4f-f90 admonition" id="vec-ex4f">
<span id="listing-vec-ex4f"></span><p class="admonition-title">Listing: <code class="docutils notranslate"><span class="pre">src/vec/vec/tutorials/ex4f.F90</span></code></p>
<div class="highlight-fortran notranslate"><div class="highlight"><pre><span></span><span class="c">!</span>
<span class="c">!</span>
<span class="c">!  Description:  Illustrates the use of <a href="../manualpages/Vec/VecSetValues.html">VecSetValues</a>() to set</span>
<span class="c">!  multiple values at once; demonstrates <a href="../manualpages/Vec/VecGetArray.html">VecGetArray</a>().</span>
<span class="c">!</span>
<span class="c">! -----------------------------------------------------------------------</span>

<span class="w">      </span><span class="k">program </span><span class="n">main</span>
<span class="cp">#include &lt;petsc/finclude/petscvec.h&gt;</span>
<span class="w">      </span><span class="k">use </span><span class="n">petscvec</span>
<span class="w">      </span><span class="k">implicit none</span>

<span class="c">! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -</span>
<span class="c">!                 Beginning of program</span>
<span class="c">! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -</span>

<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscScalar.html">PetscScalar</a></span><span class="w"> </span><span class="n">xwork</span><span class="p">(</span><span class="mi">6</span><span class="p">)</span>
<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscScalar.html">PetscScalar</a></span><span class="p">,</span><span class="w"> </span><span class="k">pointer</span><span class="w"> </span><span class="kd">::</span><span class="w"> </span><span class="n">xx_v</span><span class="p">(:),</span><span class="n">yy_v</span><span class="p">(:)</span>
<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscInt.html">PetscInt</a></span><span class="w">     </span><span class="n">i</span><span class="p">,</span><span class="n">n</span><span class="p">,</span><span class="nb">loc</span><span class="p">(</span><span class="mi">6</span><span class="p">),</span><span class="n">isix</span>
<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscErrorCode.html">PetscErrorCode</a></span><span class="w"> </span><span class="n">ierr</span>
<span class="w">       </span><span class="n"><a href="../manualpages/Vec/Vec.html">Vec</a></span><span class="w">         </span><span class="n">x</span><span class="p">,</span><span class="n">y</span>

<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Sys/PetscInitialize.html">PetscInitialize</a></span><span class="p">(</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">       </span><span class="n">n</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">6</span>
<span class="w">       </span><span class="n">isix</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">6</span>

<span class="c">!  Create initial vector and duplicate it</span>

<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecCreateSeq.html">VecCreateSeq</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Sys/PETSC_COMM_SELF.html">PETSC_COMM_SELF</a></span><span class="p">,</span><span class="n">n</span><span class="p">,</span><span class="n">x</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecDuplicate.html">VecDuplicate</a></span><span class="p">(</span><span class="n">x</span><span class="p">,</span><span class="n">y</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>

<span class="c">!  Fill work arrays with vector entries and locations.  Note that</span>
<span class="c">!  the vector indices are 0-based in PETSc (for both Fortran and</span>
<span class="c">!  C vectors)</span>

<span class="w">       </span><span class="k">do </span><span class="mi">10</span><span class="w"> </span><span class="n">i</span><span class="o">=</span><span class="mi">1</span><span class="p">,</span><span class="n">n</span>
<span class="w">          </span><span class="nb">loc</span><span class="p">(</span><span class="n">i</span><span class="p">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">i</span><span class="o">-</span><span class="mi">1</span>
<span class="w">          </span><span class="n">xwork</span><span class="p">(</span><span class="n">i</span><span class="p">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">1</span><span class="mf">0.0</span><span class="o">*</span><span class="kt">real</span><span class="p">(</span><span class="n">i</span><span class="p">)</span>
<span class="w">  </span><span class="mi">10</span><span class="w">   </span><span class="k">continue</span>

<span class="c">!  Set vector values.  Note that we set multiple entries at once.</span>
<span class="c">!  Of course, usually one would create a work array that is the</span>
<span class="c">!  natural size for a particular problem (not one that is as long</span>
<span class="c">!  as the full vector).</span>

<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecSetValues.html">VecSetValues</a></span><span class="p">(</span><span class="n">x</span><span class="p">,</span><span class="n">isix</span><span class="p">,</span><span class="nb">loc</span><span class="p">,</span><span class="n">xwork</span><span class="p">,</span><span class="n"><a href="../manualpages/Sys/INSERT_VALUES.html">INSERT_VALUES</a></span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>

<span class="c">!  Assemble vector</span>

<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecAssemblyBegin.html">VecAssemblyBegin</a></span><span class="p">(</span><span class="n">x</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecAssemblyEnd.html">VecAssemblyEnd</a></span><span class="p">(</span><span class="n">x</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>

<span class="c">!  View vector</span>
<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Sys/PetscObjectSetName.html">PetscObjectSetName</a></span><span class="p">(</span><span class="n">x</span><span class="p">,</span><span class="w"> </span><span class="s1">&#39;initial vector:&#39;</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecView.html">VecView</a></span><span class="p">(</span><span class="n">x</span><span class="p">,</span><span class="n"><a href="../manualpages/Viewer/PETSC_VIEWER_STDOUT_SELF.html">PETSC_VIEWER_STDOUT_SELF</a></span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecCopy.html">VecCopy</a></span><span class="p">(</span><span class="n">x</span><span class="p">,</span><span class="n">y</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>

<span class="c">!  Get a pointer to vector data.</span>
<span class="c">!    - For default PETSc vectors, <a href="../manualpages/Vec/VecGetArray.html">VecGetArray</a>() returns a pointer to</span>
<span class="c">!      the data array.  Otherwise, the routine is implementation dependent.</span>
<span class="c">!    - You MUST call <a href="../manualpages/Vec/VecRestoreArray.html">VecRestoreArray</a>() when you no longer need access to</span>
<span class="c">!      the array.</span>
<span class="c">!    - Note that the Fortran interface to <a href="../manualpages/Vec/VecGetArray.html">VecGetArray</a>() differs from the</span>
<span class="c">!      C version.  See the users manual for details.</span>

<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecGetArray.html">VecGetArray</a></span><span class="p">(</span><span class="n">x</span><span class="p">,</span><span class="n">xx_v</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecGetArray.html">VecGetArray</a></span><span class="p">(</span><span class="n">y</span><span class="p">,</span><span class="n">yy_v</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>

<span class="c">!  Modify vector data</span>

<span class="w">       </span><span class="k">do </span><span class="mi">30</span><span class="w"> </span><span class="n">i</span><span class="o">=</span><span class="mi">1</span><span class="p">,</span><span class="n">n</span>
<span class="w">          </span><span class="n">xx_v</span><span class="p">(</span><span class="n">i</span><span class="p">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">10</span><span class="mf">0.0</span><span class="o">*</span><span class="kt">real</span><span class="p">(</span><span class="n">i</span><span class="p">)</span>
<span class="w">          </span><span class="n">yy_v</span><span class="p">(</span><span class="n">i</span><span class="p">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">100</span><span class="mf">0.0</span><span class="o">*</span><span class="kt">real</span><span class="p">(</span><span class="n">i</span><span class="p">)</span>
<span class="w">  </span><span class="mi">30</span><span class="w">   </span><span class="k">continue</span>

<span class="c">!  Restore vectors</span>

<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecRestoreArray.html">VecRestoreArray</a></span><span class="p">(</span><span class="n">x</span><span class="p">,</span><span class="n">xx_v</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecRestoreArray.html">VecRestoreArray</a></span><span class="p">(</span><span class="n">y</span><span class="p">,</span><span class="n">yy_v</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>

<span class="c">!  View vectors</span>
<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Sys/PetscObjectSetName.html">PetscObjectSetName</a></span><span class="p">(</span><span class="n">x</span><span class="p">,</span><span class="w"> </span><span class="s1">&#39;new vector 1:&#39;</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecView.html">VecView</a></span><span class="p">(</span><span class="n">x</span><span class="p">,</span><span class="n"><a href="../manualpages/Viewer/PETSC_VIEWER_STDOUT_SELF.html">PETSC_VIEWER_STDOUT_SELF</a></span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>

<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Sys/PetscObjectSetName.html">PetscObjectSetName</a></span><span class="p">(</span><span class="n">y</span><span class="p">,</span><span class="w"> </span><span class="s1">&#39;new vector 2:&#39;</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecView.html">VecView</a></span><span class="p">(</span><span class="n">y</span><span class="p">,</span><span class="n"><a href="../manualpages/Viewer/PETSC_VIEWER_STDOUT_SELF.html">PETSC_VIEWER_STDOUT_SELF</a></span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>

<span class="c">!  Free work space.  All PETSc objects should be destroyed when they</span>
<span class="c">!  are no longer needed.</span>

<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecDestroy.html">VecDestroy</a></span><span class="p">(</span><span class="n">x</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecDestroy.html">VecDestroy</a></span><span class="p">(</span><span class="n">y</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">       </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Sys/PetscFinalize.html">PetscFinalize</a></span><span class="p">(</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">       </span><span class="k">end</span>
</pre></div>
</div>
</div>
<div class="admonition-listing-src-sys-classes-draw-tests-ex5f-f90 admonition" id="draw-test-ex5f">
<p class="admonition-title">Listing: <code class="docutils notranslate"><span class="pre">src/sys/classes/draw/tests/ex5f.F90</span></code></p>
<div class="highlight-fortran notranslate"><div class="highlight"><pre><span></span><span class="c">!</span>
<span class="c">!</span>
<span class="w">      </span><span class="k">program </span><span class="n">main</span>
<span class="cp">#include &lt;petsc/finclude/petscsys.h&gt;</span>
<span class="cp">#include &lt;petsc/finclude/petscdraw.h&gt;</span>
<span class="w">      </span><span class="k">use </span><span class="n">petscsys</span>
<span class="w">      </span><span class="k">use </span><span class="n">petscdraw</span>
<span class="w">      </span><span class="k">implicit none</span>
<span class="c">!</span>
<span class="c">!  This example demonstrates basic use of the Fortran interface for</span>
<span class="c">!  <a href="../manualpages/Draw/PetscDraw.html">PetscDraw</a> routines.</span>
<span class="c">!</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Draw/PetscDraw.html">PetscDraw</a></span><span class="w">         </span><span class="n">draw</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Draw/PetscDrawLG.html">PetscDrawLG</a></span><span class="w">       </span><span class="n">lg</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Draw/PetscDrawAxis.html">PetscDrawAxis</a></span><span class="w">     </span><span class="n">axis</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscErrorCode.html">PetscErrorCode</a></span><span class="w">    </span><span class="n">ierr</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscBool.html">PetscBool</a></span><span class="w">         </span><span class="n">flg</span>
<span class="w">      </span><span class="n">integer4</span><span class="w">         </span><span class="n">x</span><span class="p">,</span><span class="n">y</span><span class="p">,</span><span class="n">width</span><span class="p">,</span><span class="n">height</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscReal.html">PetscReal</a></span><span class="w">       </span><span class="n">xd</span><span class="p">,</span><span class="n">yd</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscReal.html">PetscReal</a></span><span class="w">         </span><span class="n">ten</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscInt.html">PetscInt</a></span><span class="w">          </span><span class="n">i</span><span class="p">,</span><span class="n">n</span><span class="p">,</span><span class="n">w</span><span class="p">,</span><span class="n">h</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscInt.html">PetscInt</a></span><span class="w">          </span><span class="n">one</span>

<span class="w">      </span><span class="n">n</span><span class="w">      </span><span class="o">=</span><span class="w"> </span><span class="mi">15</span>
<span class="w">      </span><span class="n">x</span><span class="w">      </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span>
<span class="w">      </span><span class="n">y</span><span class="w">      </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span>
<span class="w">      </span><span class="n">w</span><span class="w">      </span><span class="o">=</span><span class="w"> </span><span class="mi">400</span>
<span class="w">      </span><span class="n">h</span><span class="w">      </span><span class="o">=</span><span class="w"> </span><span class="mi">300</span>
<span class="w">      </span><span class="n">ten</span><span class="w">    </span><span class="o">=</span><span class="w"> </span><span class="mi">1</span><span class="mf">0.0</span>
<span class="w">      </span><span class="n">one</span><span class="w">    </span><span class="o">=</span><span class="w"> </span><span class="mi">1</span>

<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Sys/PetscInitialize.html">PetscInitialize</a></span><span class="p">(</span><span class="n">ierr</span><span class="p">))</span>

<span class="c">!  GetInt requires a <a href="../manualpages/Sys/PetscInt.html">PetscInt</a> so have to do this ugly setting</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Sys/PetscOptionsGetInt.html">PetscOptionsGetInt</a></span><span class="p">(</span><span class="n">PETSC_NULL_OPTIONS</span><span class="p">,</span><span class="n">PETSC_NULL_CHARACTER</span><span class="p">,</span><span class="s1">&#39;-width&#39;</span><span class="p">,</span><span class="n">w</span><span class="p">,</span><span class="w"> </span><span class="n">flg</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">      </span><span class="n">width</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nb">int</span><span class="p">(</span><span class="n">w</span><span class="p">,</span><span class="nb">kind</span><span class="o">=</span><span class="nb">kind</span><span class="p">(</span><span class="n">width</span><span class="p">))</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Sys/PetscOptionsGetInt.html">PetscOptionsGetInt</a></span><span class="p">(</span><span class="n">PETSC_NULL_OPTIONS</span><span class="p">,</span><span class="n">PETSC_NULL_CHARACTER</span><span class="p">,</span><span class="s1">&#39;-height&#39;</span><span class="p">,</span><span class="n">h</span><span class="p">,</span><span class="n">flg</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">      </span><span class="n">height</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nb">int</span><span class="p">(</span><span class="n">h</span><span class="p">,</span><span class="nb">kind</span><span class="o">=</span><span class="nb">kind</span><span class="p">(</span><span class="n">height</span><span class="p">))</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Sys/PetscOptionsGetInt.html">PetscOptionsGetInt</a></span><span class="p">(</span><span class="n">PETSC_NULL_OPTIONS</span><span class="p">,</span><span class="n">PETSC_NULL_CHARACTER</span><span class="p">,</span><span class="s1">&#39;-n&#39;</span><span class="p">,</span><span class="n">n</span><span class="p">,</span><span class="n">flg</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>

<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Draw/PetscDrawCreate.html">PetscDrawCreate</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Sys/PETSC_COMM_WORLD.html">PETSC_COMM_WORLD</a></span><span class="p">,</span><span class="n">PETSC_NULL_CHARACTER</span><span class="p">,</span><span class="n">PETSC_NULL_CHARACTER</span><span class="p">,</span><span class="n">x</span><span class="p">,</span><span class="n">y</span><span class="p">,</span><span class="n">width</span><span class="p">,</span><span class="n">height</span><span class="p">,</span><span class="n">draw</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Draw/PetscDrawSetFromOptions.html">PetscDrawSetFromOptions</a></span><span class="p">(</span><span class="n">draw</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>

<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Draw/PetscDrawLGCreate.html">PetscDrawLGCreate</a></span><span class="p">(</span><span class="n">draw</span><span class="p">,</span><span class="n">one</span><span class="p">,</span><span class="n">lg</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Draw/PetscDrawLGGetAxis.html">PetscDrawLGGetAxis</a></span><span class="p">(</span><span class="n">lg</span><span class="p">,</span><span class="n">axis</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Draw/PetscDrawAxisSetColors.html">PetscDrawAxisSetColors</a></span><span class="p">(</span><span class="n">axis</span><span class="p">,</span><span class="n">PETSC_DRAW_BLACK</span><span class="p">,</span><span class="n">PETSC_DRAW_RED</span><span class="p">,</span><span class="n">PETSC_DRAW_BLUE</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Draw/PetscDrawAxisSetLabels.html">PetscDrawAxisSetLabels</a></span><span class="p">(</span><span class="n">axis</span><span class="p">,</span><span class="s1">&#39;toplabel&#39;</span><span class="p">,</span><span class="s1">&#39;xlabel&#39;</span><span class="p">,</span><span class="s1">&#39;ylabel&#39;</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>

<span class="w">      </span><span class="k">do </span><span class="mi">10</span><span class="p">,</span><span class="w"> </span><span class="n">i</span><span class="o">=</span><span class="mi">0</span><span class="p">,</span><span class="n">n</span><span class="o">-</span><span class="mi">1</span>
<span class="w">        </span><span class="n">xd</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kt">real</span><span class="p">(</span><span class="n">i</span><span class="p">)</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mf">5.0</span>
<span class="w">        </span><span class="n">yd</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">xd</span><span class="o">*</span><span class="n">xd</span>
<span class="w">        </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Draw/PetscDrawLGAddPoint.html">PetscDrawLGAddPoint</a></span><span class="p">(</span><span class="n">lg</span><span class="p">,</span><span class="n">xd</span><span class="p">,</span><span class="n">yd</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w"> </span><span class="mi">10</span><span class="w">   </span><span class="k">continue</span>

<span class="k">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Draw/PetscDrawLGSetUseMarkers.html">PetscDrawLGSetUseMarkers</a></span><span class="p">(</span><span class="n">lg</span><span class="p">,</span><span class="n"><a href="../manualpages/Sys/PETSC_TRUE.html">PETSC_TRUE</a></span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Draw/PetscDrawLGDraw.html">PetscDrawLGDraw</a></span><span class="p">(</span><span class="n">lg</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>

<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Sys/PetscSleep.html">PetscSleep</a></span><span class="p">(</span><span class="n">ten</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>

<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Draw/PetscDrawLGDestroy.html">PetscDrawLGDestroy</a></span><span class="p">(</span><span class="n">lg</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Draw/PetscDrawDestroy.html">PetscDrawDestroy</a></span><span class="p">(</span><span class="n">draw</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Sys/PetscFinalize.html">PetscFinalize</a></span><span class="p">(</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">      </span><span class="k">end</span>
</pre></div>
</div>
</div>
<div class="admonition-listing-src-snes-tutorials-ex1f-f90 admonition" id="snes-ex1f">
<p class="admonition-title">Listing: <code class="docutils notranslate"><span class="pre">src/snes/tutorials/ex1f.F90</span></code></p>
<div class="highlight-fortran notranslate"><div class="highlight"><pre><span></span><span class="c">!</span>
<span class="c">!  Description: Uses the Newton method to solve a two-variable system.</span>
<span class="c">!</span>

<span class="w">      </span><span class="k">program </span><span class="n">main</span>
<span class="cp">#include &lt;petsc/finclude/petsc.h&gt;</span>
<span class="w">        </span><span class="k">use </span><span class="n">petsc</span>
<span class="w">      </span><span class="k">implicit none</span>

<span class="c">! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -</span>
<span class="c">!                   Variable declarations</span>
<span class="c">! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -</span>
<span class="c">!</span>
<span class="c">!  Variables:</span>
<span class="c">!     snes        - nonlinear solver</span>
<span class="c">!     ksp        - linear solver</span>
<span class="c">!     pc          - preconditioner context</span>
<span class="c">!     ksp         - Krylov subspace method context</span>
<span class="c">!     x, r        - solution, residual vectors</span>
<span class="c">!     J           - Jacobian matrix</span>
<span class="c">!     its         - iterations for convergence</span>
<span class="c">!</span>
<span class="w">      </span><span class="n"><a href="../manualpages/SNES/SNES.html">SNES</a></span><span class="w">     </span><span class="n">snes</span>
<span class="w">      </span><span class="n"><a href="../manualpages/PC/PC.html">PC</a></span><span class="w">       </span><span class="n">pc</span>
<span class="w">      </span><span class="n"><a href="../manualpages/KSP/KSP.html">KSP</a></span><span class="w">      </span><span class="n">ksp</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Vec/Vec.html">Vec</a></span><span class="w">      </span><span class="n">x</span><span class="p">,</span><span class="n">r</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Mat/Mat.html">Mat</a></span><span class="w">      </span><span class="n">J</span>
<span class="w">      </span><span class="n"><a href="../manualpages/SNES/SNESLineSearch.html">SNESLineSearch</a></span><span class="w"> </span><span class="n">linesearch</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscErrorCode.html">PetscErrorCode</a></span><span class="w">  </span><span class="n">ierr</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscInt.html">PetscInt</a></span><span class="w"> </span><span class="n">its</span><span class="p">,</span><span class="n">i2</span><span class="p">,</span><span class="n">i20</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscMPIInt.html">PetscMPIInt</a></span><span class="w"> </span><span class="n">size</span><span class="p">,</span><span class="n">rank</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscScalar.html">PetscScalar</a></span><span class="w">   </span><span class="n">pfive</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscReal.html">PetscReal</a></span><span class="w">   </span><span class="n">tol</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscBool.html">PetscBool</a></span><span class="w">   </span><span class="n">setls</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscReal.html">PetscReal</a></span><span class="p">,</span><span class="w"> </span><span class="k">pointer</span><span class="w"> </span><span class="kd">::</span><span class="w"> </span><span class="n">rhistory</span><span class="p">(:)</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscInt.html">PetscInt</a></span><span class="p">,</span><span class="w"> </span><span class="k">pointer</span><span class="w"> </span><span class="kd">::</span><span class="w"> </span><span class="n">itshistory</span><span class="p">(:)</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscInt.html">PetscInt</a></span><span class="w"> </span><span class="n">nhistory</span>
<span class="cp">#if defined(PETSC_USE_LOG)</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Viewer/PetscViewer.html">PetscViewer</a></span><span class="w"> </span><span class="n">viewer</span>
<span class="cp">#endif</span>
<span class="w">      </span><span class="kt">double precision </span><span class="n">threshold</span><span class="p">,</span><span class="n">oldthreshold</span>

<span class="c">!  Note: Any user-defined Fortran routines (such as FormJacobian)</span>
<span class="c">!  MUST be declared as external.</span>

<span class="w">      </span><span class="k">external </span><span class="n">FormFunction</span><span class="p">,</span><span class="w"> </span><span class="n">FormJacobian</span><span class="p">,</span><span class="w"> </span><span class="n">MyLineSearch</span>

<span class="c">! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -</span>
<span class="c">!                 Beginning of program</span>
<span class="c">! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -</span>

<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Sys/PetscInitialize.html">PetscInitialize</a></span><span class="p">(</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Log/PetscLogNestedBegin.html">PetscLogNestedBegin</a></span><span class="p">(</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">      </span><span class="n">threshold</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mf">1.0</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Log/PetscLogSetThreshold.html">PetscLogSetThreshold</a></span><span class="p">(</span><span class="n">threshold</span><span class="p">,</span><span class="n">oldthreshold</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">      </span><span class="n">PetscCallMPIA</span><span class="p">(</span><span class="n"><a href="http://www.mpich.org/static/docs/latest/www3/MPI_Comm_size.html#MPI_Comm_size">MPI_Comm_size</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Sys/PETSC_COMM_WORLD.html">PETSC_COMM_WORLD</a></span><span class="p">,</span><span class="n">size</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">      </span><span class="n">PetscCallMPIA</span><span class="p">(</span><span class="n"><a href="http://www.mpich.org/static/docs/latest/www3/MPI_Comm_rank.html#MPI_Comm_rank">MPI_Comm_rank</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Sys/PETSC_COMM_WORLD.html">PETSC_COMM_WORLD</a></span><span class="p">,</span><span class="n">rank</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">      </span><span class="n">PetscCheckA</span><span class="p">(</span><span class="n">size</span><span class="w"> </span><span class="p">.</span><span class="n">eq</span><span class="p">.</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="n"><a href="../manualpages/Sys/PETSC_COMM_SELF.html">PETSC_COMM_SELF</a></span><span class="p">,</span><span class="n"><a href="../manualpages/Sys/PetscErrorCode.html">PETSC_ERR_WRONG_MPI_SIZE</a></span><span class="p">,</span><span class="s1">&#39;Uniprocessor example&#39;</span><span class="p">)</span>

<span class="w">      </span><span class="n">i2</span><span class="w">  </span><span class="o">=</span><span class="w"> </span><span class="mi">2</span>
<span class="w">      </span><span class="n">i20</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">20</span>
<span class="c">! - - - - - - - - - -- - - - - - - - - - - - - - - - - - - - - - - - - -</span>
<span class="c">!  Create nonlinear solver context</span>
<span class="c">! - - - - - - - - - -- - - - - - - - - - - - - - - - - - - - - - - - - -</span>

<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/SNES/SNESCreate.html">SNESCreate</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Sys/PETSC_COMM_WORLD.html">PETSC_COMM_WORLD</a></span><span class="p">,</span><span class="n">snes</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>

<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/SNES/SNESSetConvergenceHistory.html">SNESSetConvergenceHistory</a></span><span class="p">(</span><span class="n">snes</span><span class="p">,</span><span class="n">PETSC_NULL_REAL_ARRAY</span><span class="p">,</span><span class="n">PETSC_NULL_INTEGER_ARRAY</span><span class="p">,</span><span class="n"><a href="../manualpages/Sys/PETSC_DECIDE.html">PETSC_DECIDE</a></span><span class="p">,</span><span class="n"><a href="../manualpages/Sys/PETSC_FALSE.html">PETSC_FALSE</a></span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>

<span class="c">! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -</span>
<span class="c">!  Create matrix and vector data structures; set corresponding routines</span>
<span class="c">! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -</span>

<span class="c">!  Create vectors for solution and nonlinear function</span>

<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecCreateSeq.html">VecCreateSeq</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Sys/PETSC_COMM_SELF.html">PETSC_COMM_SELF</a></span><span class="p">,</span><span class="n">i2</span><span class="p">,</span><span class="n">x</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecDuplicate.html">VecDuplicate</a></span><span class="p">(</span><span class="n">x</span><span class="p">,</span><span class="n">r</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>

<span class="c">!  Create Jacobian matrix data structure</span>

<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Mat/MatCreate.html">MatCreate</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Sys/PETSC_COMM_SELF.html">PETSC_COMM_SELF</a></span><span class="p">,</span><span class="n">J</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Mat/MatSetSizes.html">MatSetSizes</a></span><span class="p">(</span><span class="n">J</span><span class="p">,</span><span class="n"><a href="../manualpages/Sys/PETSC_DECIDE.html">PETSC_DECIDE</a></span><span class="p">,</span><span class="n"><a href="../manualpages/Sys/PETSC_DECIDE.html">PETSC_DECIDE</a></span><span class="p">,</span><span class="n">i2</span><span class="p">,</span><span class="n">i2</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Mat/MatSetFromOptions.html">MatSetFromOptions</a></span><span class="p">(</span><span class="n">J</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Mat/MatSetUp.html">MatSetUp</a></span><span class="p">(</span><span class="n">J</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>

<span class="c">!  Set function evaluation routine and vector</span>

<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/SNES/SNESSetFunction.html">SNESSetFunction</a></span><span class="p">(</span><span class="n">snes</span><span class="p">,</span><span class="n">r</span><span class="p">,</span><span class="n">FormFunction</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>

<span class="c">!  Set Jacobian matrix data structure and Jacobian evaluation routine</span>

<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/SNES/SNESSetJacobian.html">SNESSetJacobian</a></span><span class="p">(</span><span class="n">snes</span><span class="p">,</span><span class="n">J</span><span class="p">,</span><span class="n">J</span><span class="p">,</span><span class="n">FormJacobian</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>

<span class="c">! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -</span>
<span class="c">!  Customize nonlinear solver; set runtime options</span>
<span class="c">! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -</span>

<span class="c">!  Set linear solver defaults for this problem. By extracting the</span>
<span class="c">!  <a href="../manualpages/KSP/KSP.html">KSP</a>, <a href="../manualpages/KSP/KSP.html">KSP</a>, and <a href="../manualpages/PC/PC.html">PC</a> contexts from the <a href="../manualpages/SNES/SNES.html">SNES</a> context, we can then</span>
<span class="c">!  directly call any <a href="../manualpages/KSP/KSP.html">KSP</a>, <a href="../manualpages/KSP/KSP.html">KSP</a>, and <a href="../manualpages/PC/PC.html">PC</a> routines to set various options.</span>

<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/SNES/SNESGetKSP.html">SNESGetKSP</a></span><span class="p">(</span><span class="n">snes</span><span class="p">,</span><span class="n">ksp</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/KSP/KSPGetPC.html">KSPGetPC</a></span><span class="p">(</span><span class="n">ksp</span><span class="p">,</span><span class="n">pc</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/PC/PCSetType.html">PCSetType</a></span><span class="p">(</span><span class="n">pc</span><span class="p">,</span><span class="n"><a href="../manualpages/PC/PCNONE.html">PCNONE</a></span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">      </span><span class="n">tol</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mf">1.e-4</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/KSP/KSPSetTolerances.html">KSPSetTolerances</a></span><span class="p">(</span><span class="n">ksp</span><span class="p">,</span><span class="n">tol</span><span class="p">,</span><span class="n">PETSC_CURRENT_REAL</span><span class="p">,</span><span class="n">PETSC_CURRENT_REAL</span><span class="p">,</span><span class="n">i20</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>

<span class="c">!  Set <a href="../manualpages/SNES/SNES.html">SNES</a>/<a href="../manualpages/KSP/KSP.html">KSP</a>/<a href="../manualpages/KSP/KSP.html">KSP</a>/<a href="../manualpages/PC/PC.html">PC</a> runtime options, e.g.,</span>
<span class="c">!      -snes_view -snes_monitor -ksp_type &lt;ksp&gt; -pc_type &lt;pc&gt;</span>
<span class="c">!  These options will override those specified above as long as</span>
<span class="c">!  <a href="../manualpages/SNES/SNESSetFromOptions.html">SNESSetFromOptions</a>() is called _after_ any other customization</span>
<span class="c">!  routines.</span>

<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/SNES/SNESSetFromOptions.html">SNESSetFromOptions</a></span><span class="p">(</span><span class="n">snes</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>

<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Sys/PetscOptionsHasName.html">PetscOptionsHasName</a></span><span class="p">(</span><span class="n">PETSC_NULL_OPTIONS</span><span class="p">,</span><span class="n">PETSC_NULL_CHARACTER</span><span class="p">,</span><span class="s1">&#39;-setls&#39;</span><span class="p">,</span><span class="n">setls</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>

<span class="w">      </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">setls</span><span class="p">)</span><span class="w"> </span><span class="k">then</span>
<span class="k">        </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/SNES/SNESGetLineSearch.html">SNESGetLineSearch</a></span><span class="p">(</span><span class="n">snes</span><span class="p">,</span><span class="w"> </span><span class="n">linesearch</span><span class="p">,</span><span class="w"> </span><span class="n">ierr</span><span class="p">))</span>
<span class="w">        </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/SNES/SNESLineSearchSetType.html">SNESLineSearchSetType</a></span><span class="p">(</span><span class="n">linesearch</span><span class="p">,</span><span class="w"> </span><span class="s1">&#39;shell&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">ierr</span><span class="p">))</span>
<span class="w">        </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/SNES/SNESLineSearchShellSetApply.html">SNESLineSearchShellSetApply</a></span><span class="p">(</span><span class="n">linesearch</span><span class="p">,</span><span class="w"> </span><span class="n">MyLineSearch</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">      </span><span class="k">endif</span>

<span class="c">! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -</span>
<span class="c">!  Evaluate initial guess; then solve nonlinear system</span>
<span class="c">! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -</span>

<span class="c">!  Note: The user should initialize the vector, x, with the initial guess</span>
<span class="c">!  for the nonlinear solver prior to calling <a href="../manualpages/SNES/SNESSolve.html">SNESSolve</a>().  In particular,</span>
<span class="c">!  to employ an initial guess of zero, the user should explicitly set</span>
<span class="c">!  this vector to zero by calling <a href="../manualpages/Vec/VecSet.html">VecSet</a>().</span>

<span class="w">      </span><span class="n">pfive</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mf">0.5</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecSet.html">VecSet</a></span><span class="p">(</span><span class="n">x</span><span class="p">,</span><span class="n">pfive</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/SNES/SNESSolve.html">SNESSolve</a></span><span class="p">(</span><span class="n">snes</span><span class="p">,</span><span class="n">PETSC_NULL_VEC</span><span class="p">,</span><span class="n">x</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>

<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/SNES/SNESGetConvergenceHistory.html">SNESGetConvergenceHistory</a></span><span class="p">(</span><span class="n">snes</span><span class="p">,</span><span class="n">rhistory</span><span class="p">,</span><span class="n">itshistory</span><span class="p">,</span><span class="n">nhistory</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n">SNESRestoreConvergenceHistory</span><span class="p">(</span><span class="n">snes</span><span class="p">,</span><span class="n">rhistory</span><span class="p">,</span><span class="n">itshistory</span><span class="p">,</span><span class="n">nhistory</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>

<span class="c">! View solver converged reason; we could instead use the option -snes_converged_reason</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/SNES/SNESConvergedReasonView.html">SNESConvergedReasonView</a></span><span class="p">(</span><span class="n">snes</span><span class="p">,</span><span class="n"><a href="../manualpages/Viewer/PETSC_VIEWER_STDOUT_WORLD.html">PETSC_VIEWER_STDOUT_WORLD</a></span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>

<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/SNES/SNESGetIterationNumber.html">SNESGetIterationNumber</a></span><span class="p">(</span><span class="n">snes</span><span class="p">,</span><span class="n">its</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">      </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">rank</span><span class="w"> </span><span class="p">.</span><span class="n">eq</span><span class="p">.</span><span class="w"> </span><span class="mi">0</span><span class="p">)</span><span class="w"> </span><span class="k">then</span>
<span class="k">         write</span><span class="p">(</span><span class="mi">6</span><span class="p">,</span><span class="mi">100</span><span class="p">)</span><span class="w"> </span><span class="n">its</span>
<span class="w">      </span><span class="k">endif</span>
<span class="k">  </span><span class="mi">100</span><span class="w"> </span><span class="k">format</span><span class="p">(</span><span class="s1">&#39;Number of <a href="../manualpages/SNES/SNES.html">SNES</a> iterations = &#39;</span><span class="p">,</span><span class="n">i5</span><span class="p">)</span>

<span class="c">! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -</span>
<span class="c">!  Free work space.  All PETSc objects should be destroyed when they</span>
<span class="c">!  are no longer needed.</span>
<span class="c">! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -</span>

<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecDestroy.html">VecDestroy</a></span><span class="p">(</span><span class="n">x</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecDestroy.html">VecDestroy</a></span><span class="p">(</span><span class="n">r</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Mat/MatDestroy.html">MatDestroy</a></span><span class="p">(</span><span class="n">J</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/SNES/SNESDestroy.html">SNESDestroy</a></span><span class="p">(</span><span class="n">snes</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="cp">#if defined(PETSC_USE_LOG)</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Viewer/PetscViewerASCIIOpen.html">PetscViewerASCIIOpen</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Sys/PETSC_COMM_WORLD.html">PETSC_COMM_WORLD</a></span><span class="p">,</span><span class="s1">&#39;filename.xml&#39;</span><span class="p">,</span><span class="n">viewer</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Viewer/PetscViewerPushFormat.html">PetscViewerPushFormat</a></span><span class="p">(</span><span class="n">viewer</span><span class="p">,</span><span class="n"><a href="../manualpages/Viewer/PetscViewerFormat.html">PETSC_VIEWER_ASCII_XML</a></span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Log/PetscLogView.html">PetscLogView</a></span><span class="p">(</span><span class="n">viewer</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Viewer/PetscViewerDestroy.html">PetscViewerDestroy</a></span><span class="p">(</span><span class="n">viewer</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="cp">#endif</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCallA.html">PetscCallA</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Sys/PetscFinalize.html">PetscFinalize</a></span><span class="p">(</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">      </span><span class="k">end</span>
<span class="c">!</span>
<span class="c">! ------------------------------------------------------------------------</span>
<span class="c">!</span>
<span class="c">!  FormFunction - Evaluates nonlinear function, F(x).</span>
<span class="c">!</span>
<span class="c">!  Input Parameters:</span>
<span class="c">!  snes - the <a href="../manualpages/SNES/SNES.html">SNES</a> context</span>
<span class="c">!  x - input vector</span>
<span class="c">!  dummy - optional user-defined context (not used here)</span>
<span class="c">!</span>
<span class="c">!  Output Parameter:</span>
<span class="c">!  f - function vector</span>
<span class="c">!</span>
<span class="w">      </span><span class="k">subroutine </span><span class="n">FormFunction</span><span class="p">(</span><span class="n">snes</span><span class="p">,</span><span class="n">x</span><span class="p">,</span><span class="n">f</span><span class="p">,</span><span class="n">dummy</span><span class="p">,</span><span class="n">ierr</span><span class="p">)</span>
<span class="w">      </span><span class="k">use </span><span class="n">petscvec</span>
<span class="w">      </span><span class="k">use </span><span class="n">petscsnesdef</span>
<span class="w">      </span><span class="k">implicit none</span>

<span class="k">      </span><span class="n"><a href="../manualpages/SNES/SNES.html">SNES</a></span><span class="w">     </span><span class="n">snes</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Vec/Vec.html">Vec</a></span><span class="w">      </span><span class="n">x</span><span class="p">,</span><span class="n">f</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscErrorCode.html">PetscErrorCode</a></span><span class="w"> </span><span class="n">ierr</span>
<span class="w">      </span><span class="kt">integer </span><span class="n">dummy</span><span class="p">(</span><span class="o">*</span><span class="p">)</span>

<span class="c">!  Declarations for use with local arrays</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscScalar.html">PetscScalar</a></span><span class="p">,</span><span class="k">pointer</span><span class="w"> </span><span class="kd">::</span><span class="w"> </span><span class="n">lx_v</span><span class="p">(:),</span><span class="n">lf_v</span><span class="p">(:)</span>

<span class="c">!  Get pointers to vector data.</span>
<span class="c">!    - <a href="../manualpages/Vec/VecGetArray.html">VecGetArray</a>() returns a pointer to the data array.</span>
<span class="c">!    - You MUST call <a href="../manualpages/Vec/VecRestoreArray.html">VecRestoreArray</a>() when you no longer need access to</span>
<span class="c">!      the array.</span>

<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCall.html">PetscCall</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecGetArrayRead.html">VecGetArrayRead</a></span><span class="p">(</span><span class="n">x</span><span class="p">,</span><span class="n">lx_v</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCall.html">PetscCall</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecGetArray.html">VecGetArray</a></span><span class="p">(</span><span class="n">f</span><span class="p">,</span><span class="n">lf_v</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>

<span class="c">!  Compute function</span>

<span class="w">      </span><span class="n">lf_v</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">lx_v</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span><span class="o">*</span><span class="n">lx_v</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">lx_v</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span><span class="o">*</span><span class="n">lx_v</span><span class="p">(</span><span class="mi">2</span><span class="p">)</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mf">3.0</span>
<span class="w">      </span><span class="n">lf_v</span><span class="p">(</span><span class="mi">2</span><span class="p">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">lx_v</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span><span class="o">*</span><span class="n">lx_v</span><span class="p">(</span><span class="mi">2</span><span class="p">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">lx_v</span><span class="p">(</span><span class="mi">2</span><span class="p">)</span><span class="o">*</span><span class="n">lx_v</span><span class="p">(</span><span class="mi">2</span><span class="p">)</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mf">6.0</span>

<span class="c">!  Restore vectors</span>

<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCall.html">PetscCall</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecRestoreArrayRead.html">VecRestoreArrayRead</a></span><span class="p">(</span><span class="n">x</span><span class="p">,</span><span class="n">lx_v</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCall.html">PetscCall</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecRestoreArray.html">VecRestoreArray</a></span><span class="p">(</span><span class="n">f</span><span class="p">,</span><span class="n">lf_v</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>

<span class="w">      </span><span class="k">end</span>

<span class="c">! ---------------------------------------------------------------------</span>
<span class="c">!</span>
<span class="c">!  FormJacobian - Evaluates Jacobian matrix.</span>
<span class="c">!</span>
<span class="c">!  Input Parameters:</span>
<span class="c">!  snes - the <a href="../manualpages/SNES/SNES.html">SNES</a> context</span>
<span class="c">!  x - input vector</span>
<span class="c">!  dummy - optional user-defined context (not used here)</span>
<span class="c">!</span>
<span class="c">!  Output Parameters:</span>
<span class="c">!  A - Jacobian matrix</span>
<span class="c">!  B - optionally different preconditioning matrix</span>
<span class="c">!</span>
<span class="w">      </span><span class="k">subroutine </span><span class="n">FormJacobian</span><span class="p">(</span><span class="n">snes</span><span class="p">,</span><span class="n">X</span><span class="p">,</span><span class="n">jac</span><span class="p">,</span><span class="n">B</span><span class="p">,</span><span class="n">dummy</span><span class="p">,</span><span class="n">ierr</span><span class="p">)</span>
<span class="w">      </span><span class="k">use </span><span class="n">petscvec</span>
<span class="w">      </span><span class="k">use </span><span class="n">petscmat</span>
<span class="w">      </span><span class="k">use </span><span class="n">petscsnesdef</span>
<span class="w">      </span><span class="k">implicit none</span>

<span class="k">      </span><span class="n"><a href="../manualpages/SNES/SNES.html">SNES</a></span><span class="w">         </span><span class="n">snes</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Vec/Vec.html">Vec</a></span><span class="w">          </span><span class="n">X</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Mat/Mat.html">Mat</a></span><span class="w">          </span><span class="n">jac</span><span class="p">,</span><span class="n">B</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscScalar.html">PetscScalar</a></span><span class="w">  </span><span class="n">A</span><span class="p">(</span><span class="mi">4</span><span class="p">)</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscErrorCode.html">PetscErrorCode</a></span><span class="w"> </span><span class="n">ierr</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscInt.html">PetscInt</a></span><span class="w"> </span><span class="n">idx</span><span class="p">(</span><span class="mi">2</span><span class="p">),</span><span class="n">i2</span>
<span class="w">      </span><span class="kt">integer </span><span class="n">dummy</span><span class="p">(</span><span class="o">*</span><span class="p">)</span>

<span class="c">!  Declarations for use with local arrays</span>

<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscScalar.html">PetscScalar</a></span><span class="p">,</span><span class="k">pointer</span><span class="w"> </span><span class="kd">::</span><span class="w"> </span><span class="n">lx_v</span><span class="p">(:)</span>

<span class="c">!  Get pointer to vector data</span>

<span class="w">      </span><span class="n">i2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">2</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCall.html">PetscCall</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecGetArrayRead.html">VecGetArrayRead</a></span><span class="p">(</span><span class="n">x</span><span class="p">,</span><span class="n">lx_v</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>

<span class="c">!  Compute Jacobian entries and insert into matrix.</span>
<span class="c">!   - Since this is such a small problem, we set all entries for</span>
<span class="c">!     the matrix at once.</span>
<span class="c">!   - Note that <a href="../manualpages/Mat/MatSetValues.html">MatSetValues</a>() uses 0-based row and column numbers</span>
<span class="c">!     in Fortran as well as in C (as set here in the array idx).</span>

<span class="w">      </span><span class="n">idx</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span>
<span class="w">      </span><span class="n">idx</span><span class="p">(</span><span class="mi">2</span><span class="p">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">1</span>
<span class="w">      </span><span class="n">A</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mf">2.0</span><span class="o">*</span><span class="n">lx_v</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">lx_v</span><span class="p">(</span><span class="mi">2</span><span class="p">)</span>
<span class="w">      </span><span class="n">A</span><span class="p">(</span><span class="mi">2</span><span class="p">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">lx_v</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
<span class="w">      </span><span class="n">A</span><span class="p">(</span><span class="mi">3</span><span class="p">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">lx_v</span><span class="p">(</span><span class="mi">2</span><span class="p">)</span>
<span class="w">      </span><span class="n">A</span><span class="p">(</span><span class="mi">4</span><span class="p">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">lx_v</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mf">2.0</span><span class="o">*</span><span class="n">lx_v</span><span class="p">(</span><span class="mi">2</span><span class="p">)</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCall.html">PetscCall</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Mat/MatSetValues.html">MatSetValues</a></span><span class="p">(</span><span class="n">B</span><span class="p">,</span><span class="n">i2</span><span class="p">,</span><span class="n">idx</span><span class="p">,</span><span class="n">i2</span><span class="p">,</span><span class="n">idx</span><span class="p">,</span><span class="n">A</span><span class="p">,</span><span class="n"><a href="../manualpages/Sys/INSERT_VALUES.html">INSERT_VALUES</a></span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>

<span class="c">!  Restore vector</span>

<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCall.html">PetscCall</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecRestoreArrayRead.html">VecRestoreArrayRead</a></span><span class="p">(</span><span class="n">x</span><span class="p">,</span><span class="n">lx_v</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>

<span class="c">!  Assemble matrix</span>

<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCall.html">PetscCall</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Mat/MatAssemblyBegin.html">MatAssemblyBegin</a></span><span class="p">(</span><span class="n">B</span><span class="p">,</span><span class="n"><a href="../manualpages/Mat/MatAssemblyType.html">MAT_FINAL_ASSEMBLY</a></span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCall.html">PetscCall</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Mat/MatAssemblyEnd.html">MatAssemblyEnd</a></span><span class="p">(</span><span class="n">B</span><span class="p">,</span><span class="n"><a href="../manualpages/Mat/MatAssemblyType.html">MAT_FINAL_ASSEMBLY</a></span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">      </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">B</span><span class="w"> </span><span class="p">.</span><span class="n">ne</span><span class="p">.</span><span class="w"> </span><span class="n">jac</span><span class="p">)</span><span class="w"> </span><span class="k">then</span>
<span class="k">        </span><span class="n"><a href="../manualpages/Sys/PetscCall.html">PetscCall</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Mat/MatAssemblyBegin.html">MatAssemblyBegin</a></span><span class="p">(</span><span class="n">jac</span><span class="p">,</span><span class="n"><a href="../manualpages/Mat/MatAssemblyType.html">MAT_FINAL_ASSEMBLY</a></span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">        </span><span class="n"><a href="../manualpages/Sys/PetscCall.html">PetscCall</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Mat/MatAssemblyEnd.html">MatAssemblyEnd</a></span><span class="p">(</span><span class="n">jac</span><span class="p">,</span><span class="n"><a href="../manualpages/Mat/MatAssemblyType.html">MAT_FINAL_ASSEMBLY</a></span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">      </span><span class="k">endif</span>

<span class="k">      end</span>

<span class="k">      subroutine </span><span class="n">MyLineSearch</span><span class="p">(</span><span class="n">linesearch</span><span class="p">,</span><span class="w"> </span><span class="n">lctx</span><span class="p">,</span><span class="w"> </span><span class="n">ierr</span><span class="p">)</span>
<span class="w">      </span><span class="k">use </span><span class="n">petscsnes</span>
<span class="w">      </span><span class="k">use </span><span class="n">petscvec</span>
<span class="w">      </span><span class="k">implicit none</span>

<span class="k">      </span><span class="n"><a href="../manualpages/SNES/SNESLineSearch.html">SNESLineSearch</a></span><span class="w">    </span><span class="n">linesearch</span>
<span class="w">      </span><span class="n"><a href="../manualpages/SNES/SNES.html">SNES</a></span><span class="w">              </span><span class="n">snes</span>
<span class="w">      </span><span class="kt">integer           </span><span class="n">lctx</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Vec/Vec.html">Vec</a></span><span class="w">               </span><span class="n">x</span><span class="p">,</span><span class="w"> </span><span class="n">f</span><span class="p">,</span><span class="n">g</span><span class="p">,</span><span class="w"> </span><span class="n">y</span><span class="p">,</span><span class="w"> </span><span class="n">w</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscReal.html">PetscReal</a></span><span class="w">         </span><span class="n">ynorm</span><span class="p">,</span><span class="n">gnorm</span><span class="p">,</span><span class="n">xnorm</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscErrorCode.html">PetscErrorCode</a></span><span class="w">    </span><span class="n">ierr</span>

<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscScalar.html">PetscScalar</a></span><span class="w">       </span><span class="n">mone</span>

<span class="w">      </span><span class="n">mone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">-</span><span class="mf">1.0</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCall.html">PetscCall</a></span><span class="p">(</span><span class="n"><a href="../manualpages/SNES/SNESLineSearchGetSNES.html">SNESLineSearchGetSNES</a></span><span class="p">(</span><span class="n">linesearch</span><span class="p">,</span><span class="w"> </span><span class="n">snes</span><span class="p">,</span><span class="w"> </span><span class="n">ierr</span><span class="p">))</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCall.html">PetscCall</a></span><span class="p">(</span><span class="n"><a href="../manualpages/SNES/SNESLineSearchGetVecs.html">SNESLineSearchGetVecs</a></span><span class="p">(</span><span class="n">linesearch</span><span class="p">,</span><span class="w"> </span><span class="n">x</span><span class="p">,</span><span class="w"> </span><span class="n">f</span><span class="p">,</span><span class="w"> </span><span class="n">y</span><span class="p">,</span><span class="w"> </span><span class="n">w</span><span class="p">,</span><span class="w"> </span><span class="n">g</span><span class="p">,</span><span class="w"> </span><span class="n">ierr</span><span class="p">))</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCall.html">PetscCall</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecNorm.html">VecNorm</a></span><span class="p">(</span><span class="n">y</span><span class="p">,</span><span class="n"><a href="../manualpages/Vec/NORM_2.html">NORM_2</a></span><span class="p">,</span><span class="n">ynorm</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCall.html">PetscCall</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecAXPY.html">VecAXPY</a></span><span class="p">(</span><span class="n">x</span><span class="p">,</span><span class="n">mone</span><span class="p">,</span><span class="n">y</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCall.html">PetscCall</a></span><span class="p">(</span><span class="n"><a href="../manualpages/SNES/SNESComputeFunction.html">SNESComputeFunction</a></span><span class="p">(</span><span class="n">snes</span><span class="p">,</span><span class="n">x</span><span class="p">,</span><span class="n">f</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCall.html">PetscCall</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecNorm.html">VecNorm</a></span><span class="p">(</span><span class="n">f</span><span class="p">,</span><span class="n"><a href="../manualpages/Vec/NORM_2.html">NORM_2</a></span><span class="p">,</span><span class="n">gnorm</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCall.html">PetscCall</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecNorm.html">VecNorm</a></span><span class="p">(</span><span class="n">x</span><span class="p">,</span><span class="n"><a href="../manualpages/Vec/NORM_2.html">NORM_2</a></span><span class="p">,</span><span class="n">xnorm</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCall.html">PetscCall</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Vec/VecNorm.html">VecNorm</a></span><span class="p">(</span><span class="n">y</span><span class="p">,</span><span class="n"><a href="../manualpages/Vec/NORM_2.html">NORM_2</a></span><span class="p">,</span><span class="n">ynorm</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">      </span><span class="n"><a href="../manualpages/Sys/PetscCall.html">PetscCall</a></span><span class="p">(</span><span class="n"><a href="../manualpages/SNES/SNESLineSearchSetNorms.html">SNESLineSearchSetNorms</a></span><span class="p">(</span><span class="n">linesearch</span><span class="p">,</span><span class="w"> </span><span class="n">xnorm</span><span class="p">,</span><span class="w"> </span><span class="n">gnorm</span><span class="p">,</span><span class="w"> </span><span class="n">ynorm</span><span class="p">,</span><span class="n">ierr</span><span class="p">))</span>
<span class="w">      </span><span class="k">end</span>
</pre></div>
</div>
</div>
<section id="calling-fortran-routines-from-c-and-c-routines-from-fortran">
<h3>Calling Fortran Routines from C (and C Routines from Fortran)<a class="headerlink" href="#calling-fortran-routines-from-c-and-c-routines-from-fortran" title="Link to this heading">#</a></h3>
<p>The information here applies only if you plan to call your <strong>own</strong>
C functions from Fortran or Fortran functions from C.
Different compilers have different methods of naming Fortran routines
called from C (or C routines called from Fortran). Most Fortran
compilers change the capital letters in Fortran routines to
all lowercase. With some compilers, the Fortran compiler appends an underscore
to the end of each Fortran routine name; for example, the Fortran
routine <code class="docutils notranslate"><span class="pre">Dabsc()</span></code> would be called from C with <code class="docutils notranslate"><span class="pre">dabsc_()</span></code>. Other
compilers change all the letters in Fortran routine names to capitals.</p>
<p>PETSc provides two macros (defined in C/C++) to help write portable code
that mixes C/C++ and Fortran. They are <code class="docutils notranslate"><span class="pre">PETSC_HAVE_FORTRAN_UNDERSCORE</span></code>
and <code class="docutils notranslate"><span class="pre">PETSC_HAVE_FORTRAN_CAPS</span></code> , which will be defined in the file
<code class="docutils notranslate"><span class="pre">$PETSC_DIR/$PETSC_ARCH/include/petscconf.h</span></code> based on the compilers
conventions. The macros are used,
for example, as follows:</p>
<div class="highlight-fortran notranslate"><div class="highlight"><pre><span></span><span class="cp">#if defined(PETSC_HAVE_FORTRAN_CAPS)</span>
<span class="cp">#define dabsc_ DABSC</span>
<span class="cp">#elif !defined(PETSC_HAVE_FORTRAN_UNDERSCORE)</span>
<span class="cp">#define dabsc_ dabsc</span>
<span class="cp">#endif</span>
<span class="p">.....</span>
<span class="n">dabsc_</span><span class="p">(</span><span class="w"> </span><span class="p">&amp;</span><span class="n">n</span><span class="p">,</span><span class="n">x</span><span class="p">,</span><span class="n">y</span><span class="p">);</span><span class="w"> </span><span class="o">/*</span><span class="w"> </span><span class="k">call </span><span class="n">the</span><span class="w"> </span><span class="n">Fortran</span><span class="w"> </span><span class="k">function</span><span class="w"> </span><span class="o">*/</span>
</pre></div>
</div>
</section>
</section>
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