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<section class="tex2jax_ignore mathjax_ignore" id="basic-object-design-and-implementation">
<h1>Basic Object Design and Implementation<a class="headerlink" href="#basic-object-design-and-implementation" title="Link to this heading">#</a></h1>
<p>PETSc is designed by using strong data encapsulation. Hence, any
collection of data (for instance, a sparse matrix) is stored in a way
that is completely private from the application code. The application
code can manipulate the data only through a well-defined interface,
since it does <em>not</em> “know” how the data is stored internally.</p>
<section id="introduction">
<h2>Introduction<a class="headerlink" href="#introduction" title="Link to this heading">#</a></h2>
<p>PETSc is designed around several classes including <code class="docutils notranslate"><span class="pre"><a href="../manualpages/Vec/Vec.html">Vec</a></span></code> (vectors) and
<code class="docutils notranslate"><span class="pre"><a href="../manualpages/Mat/Mat.html">Mat</a></span></code> (matrices, both dense and sparse). Each class is implemented by
using a C <code class="docutils notranslate"><span class="pre">struct</span></code> that contains the data and function pointers for
operations on the data (much like virtual functions in C++ classes).
Each class consists of three parts:</p>
<p>A (small) common part shared by all PETSc classes (for example, both
<code class="docutils notranslate"><span class="pre"><a href="../manualpages/KSP/KSP.html">KSP</a></span></code> and <code class="docutils notranslate"><span class="pre"><a href="../manualpages/PC/PC.html">PC</a></span></code> have this same header).</p>
<p>Another common part shared by all PETSc implementations of the class
(for example, both <code class="docutils notranslate"><span class="pre"><a href="../manualpages/KSP/KSPGMRES.html">KSPGMRES</a></span></code> and <code class="docutils notranslate"><span class="pre"><a href="../manualpages/KSP/KSPCG.html">KSPCG</a></span></code> have this common
subheader).</p>
<p>A private part used by only one particular implementation written in
PETSc.</p>
<p>For example, all matrix (<code class="docutils notranslate"><span class="pre"><a href="../manualpages/Mat/Mat.html">Mat</a></span></code>) classes share a function table of
operations that may be performed on the matrix; all PETSc matrix
implementations share some additional data fields, including matrix
parallel layout, while a particular matrix implementation in PETSc (say
compressed sparse row) has its own data fields for storing the actual
matrix values and sparsity pattern. This will be explained in more
detail in the following sections. New class implementations <em>must</em> use
the PETSc common part.</p>
<p>We will use <code class="docutils notranslate"><span class="pre"><class>_<implementation></span></code> to denote the actual source code
and data structures used for a particular implementation of an object
that has the <code class="docutils notranslate"><span class="pre"><class></span></code> interface.</p>
</section>
<section id="organization-of-the-source-code">
<h2>Organization of the Source Code<a class="headerlink" href="#organization-of-the-source-code" title="Link to this heading">#</a></h2>
<p>Each class has the following organization.</p>
<p>Its own, application-public, include file <code class="docutils notranslate"><span class="pre">include/petsc<class>.h</span></code>.</p>
<p>Its own directory, <code class="docutils notranslate"><span class="pre">src/<class></span></code> or <code class="docutils notranslate"><span class="pre">src/<package>/<class></span></code>.</p>
<p>A data structure defined in the file
<code class="docutils notranslate"><span class="pre">include/petsc/private/<class>impl.h</span></code>. This data structure is shared
by all the different PETSc implementations of the class. For example,
for matrices it is shared by dense, sparse, parallel, and sequential
formats.</p>
<p>An abstract interface that defines the application-callable functions
for the class. These are defined in the directory
<code class="docutils notranslate"><span class="pre">src/<class>/interface</span></code>. This is how polymorphism is supported with
code that implements the abstract interface to the operations on the
object. Essentially, these routines do some error checking of arguments
and logging of profiling information and then call the function
appropriate for the particular implementation of the object. The name of
the abstract function is <code class="docutils notranslate"><span class="pre"><class>Operation</span></code>, for instance,
<code class="docutils notranslate"><span class="pre"><a href="../manualpages/Mat/MatMult.html">MatMult</a>()</span></code> or <code class="docutils notranslate"><span class="pre"><a href="../manualpages/PC/PCCreate.html">PCCreate</a>(</span></code>), while the name of a particular
implementation is <code class="docutils notranslate"><span class="pre"><class>Operation_<implementation></span></code>, for instance,
<code class="docutils notranslate"><span class="pre">MatMult_SeqAIJ()</span></code> or <code class="docutils notranslate"><span class="pre">PCCreate_ILU()</span></code>. These naming conventions are
used to simplify code maintenance (also see Section [sec:stylenames]).</p>
<p>One or more actual implementations of the class (for example, sparse
uniprocessor and parallel matrices implemented with the AIJ storage
format). These are each in a subdirectory of <code class="docutils notranslate"><span class="pre">src/<class>/impls</span></code>.
Except in rare circumstances, data structures defined here should not be
referenced from outside this directory.</p>
<p>Each type of object (for instance, a vector) is defined in its own
public include file, by <code class="docutils notranslate"><span class="pre">typedef</span> <span class="pre">_p_<class>*</span> <span class="pre"><class></span></code>; (for example,
<code class="docutils notranslate"><span class="pre">typedef</span> <span class="pre">_p_Vec*</span> <span class="pre"><a href="../manualpages/Vec/Vec.html">Vec</a>;</span></code>). This organization allows the compiler to
perform type checking on all subroutine calls while at the same time
completely removing the details of the implementation of <code class="docutils notranslate"><span class="pre">_p_<class></span></code>
from the application code. This capability is extremely important
because it allows the library internals to be changed without altering
or recompiling the application code.</p>
</section>
<section id="common-object-header">
<h2>Common Object Header<a class="headerlink" href="#common-object-header" title="Link to this heading">#</a></h2>
<p>All PETSc objects (derived from the base class <code class="docutils notranslate"><span class="pre"><a href="../manualpages/Sys/PetscObject.html">PetscObject</a></span></code>) have the following common header structures
defined in
<a href="../include/petsc/private/petscimpl.h.html">include/petsc/private/petscimpl.h</a></p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="k">typedef</span><span class="w"> </span><span class="k">struct</span><span class="w"> </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="p">(</span><span class="o">*</span><span class="n">getcomm</span><span class="p">)(</span><span class="n"><a href="../manualpages/Sys/PetscObject.html">PetscObject</a></span><span class="p">,</span><span class="n"><a href="../manualpages/Sys/MPI_Comm.html">MPI_Comm</a></span><span class="o">*</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="p">(</span><span class="o">*</span><span class="n">view</span><span class="p">)(</span><span class="n"><a href="../manualpages/Sys/PetscObject.html">PetscObject</a></span><span class="p">,</span><span class="n">Viewer</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="p">(</span><span class="o">*</span><span class="n">destroy</span><span class="p">)(</span><span class="n"><a href="../manualpages/Sys/PetscObject.html">PetscObject</a></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="p">(</span><span class="o">*</span><span class="n">query</span><span class="p">)(</span><span class="n"><a href="../manualpages/Sys/PetscObject.html">PetscObject</a></span><span class="p">,</span><span class="k">const</span><span class="w"> </span><span class="kt">char</span><span class="o">*</span><span class="p">,</span><span class="n"><a href="../manualpages/Sys/PetscObject.html">PetscObject</a></span><span class="o">*</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="p">(</span><span class="o">*</span><span class="n">compose</span><span class="p">)(</span><span class="n"><a href="../manualpages/Sys/PetscObject.html">PetscObject</a></span><span class="p">,</span><span class="k">const</span><span class="w"> </span><span class="kt">char</span><span class="o">*</span><span class="p">,</span><span class="n"><a href="../manualpages/Sys/PetscObject.html">PetscObject</a></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="p">(</span><span class="o">*</span><span class="n">composefunction</span><span class="p">)(</span><span class="n"><a href="../manualpages/Sys/PetscObject.html">PetscObject</a></span><span class="p">,</span><span class="k">const</span><span class="w"> </span><span class="kt">char</span><span class="o">*</span><span class="p">,</span><span class="kt">void</span><span class="p">(</span><span class="o">*</span><span class="p">)(</span><span class="kt">void</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="p">(</span><span class="o">*</span><span class="n">queryfunction</span><span class="p">)(</span><span class="n"><a href="../manualpages/Sys/PetscObject.html">PetscObject</a></span><span class="p">,</span><span class="k">const</span><span class="w"> </span><span class="kt">char</span><span class="o">*</span><span class="p">,</span><span class="kt">void</span><span class="w"> </span><span class="p">(</span><span class="o">**</span><span class="p">)(</span><span class="kt">void</span><span class="p">));</span>
<span class="p">}</span><span class="w"> </span><span class="n">PetscOps</span><span class="p">;</span>
</pre></div>
</div>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="k">struct</span><span class="w"> </span><span class="nc">_p_</span><span class="o"><</span><span class="n">class</span><span class="o">></span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n"><a href="../manualpages/Sys/PetscClassId.html">PetscClassId</a></span><span class="w"> </span><span class="n">classid</span><span class="p">;</span>
<span class="w"> </span><span class="n">PetscOps</span><span class="w"> </span><span class="o">*</span><span class="n">bops</span><span class="p">;</span>
<span class="w"> </span><span class="o"><</span><span class="n">class</span><span class="o">></span><span class="n">Ops</span><span class="w"> </span><span class="o">*</span><span class="n">ops</span><span class="p">;</span>
<span class="w"> </span><span class="n"><a href="../manualpages/Sys/MPI_Comm.html">MPI_Comm</a></span><span class="w"> </span><span class="n">comm</span><span class="p">;</span>
<span class="w"> </span><span class="n"><a href="../manualpages/Sys/PetscLogDouble.html">PetscLogDouble</a></span><span class="w"> </span><span class="n">flops</span><span class="p">,</span><span class="n">time</span><span class="p">,</span><span class="n">mem</span><span class="p">;</span>
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">id</span><span class="p">;</span>
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">refct</span><span class="p">;</span>
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">tag</span><span class="p">;</span>
<span class="w"> </span><span class="n">DLList</span><span class="w"> </span><span class="n">qlist</span><span class="p">;</span>
<span class="w"> </span><span class="n">OList</span><span class="w"> </span><span class="n">olist</span><span class="p">;</span>
<span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">type_name</span><span class="p">;</span>
<span class="w"> </span><span class="n"><a href="../manualpages/Sys/PetscObject.html">PetscObject</a></span><span class="w"> </span><span class="n">parent</span><span class="p">;</span>
<span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">name</span><span class="p">;</span>
<span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">prefix</span><span class="p">;</span>
<span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="o">*</span><span class="n">cpp</span><span class="p">;</span>
<span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="o">**</span><span class="n">fortran_func_pointers</span><span class="p">;</span>
<span class="w"> </span><span class="p">..........</span>
<span class="w"> </span><span class="n">CLASS</span><span class="o">-</span><span class="n">SPECIFIC</span><span class="w"> </span><span class="n">DATASTRUCTURES</span>
<span class="p">};</span>
</pre></div>
</div>
<p>Here <code class="docutils notranslate"><span class="pre"><class>ops</span></code> is a function table (like the <code class="docutils notranslate"><span class="pre">PetscOps</span></code> above)
that contains the function pointers for the operations specific to that
class. For example, the PETSc vector class object operations in
<a href="../include/petsc/private/vecimpl.h.html">include/petsc/private/vecimpl.h</a>
include the following.</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="k">typedef</span><span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="nc">_VecOps</span><span class="o">*</span><span class="w"> </span><span class="n">VecOps</span><span class="p">;</span>
<span class="k">struct</span><span class="w"> </span><span class="nc">_VecOps</span><span class="w"> </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="p">(</span><span class="o">*</span><span class="n">duplicate</span><span class="p">)(</span><span class="n"><a href="../manualpages/Vec/Vec.html">Vec</a></span><span class="p">,</span><span class="n"><a href="../manualpages/Vec/Vec.html">Vec</a></span><span class="o">*</span><span class="p">);</span><span class="w"> </span><span class="cm">/* get single vector */</span>
<span class="w"> </span><span class="n"><a href="../manualpages/Sys/PetscErrorCode.html">PetscErrorCode</a></span><span class="w"> </span><span class="p">(</span><span class="o">*</span><span class="n">duplicatevecs</span><span class="p">)(</span><span class="n"><a href="../manualpages/Vec/Vec.html">Vec</a></span><span class="p">,</span><span class="n"><a href="../manualpages/Sys/PetscInt.html">PetscInt</a></span><span class="p">,</span><span class="n"><a href="../manualpages/Vec/Vec.html">Vec</a></span><span class="o">**</span><span class="p">);</span><span class="w"> </span><span class="cm">/* get array of vectors */</span>
<span class="w"> </span><span class="n"><a href="../manualpages/Sys/PetscErrorCode.html">PetscErrorCode</a></span><span class="w"> </span><span class="p">(</span><span class="o">*</span><span class="n">destroyvecs</span><span class="p">)(</span><span class="n"><a href="../manualpages/Sys/PetscInt.html">PetscInt</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="cm">/* free array of vectors */</span>
<span class="w"> </span><span class="n"><a href="../manualpages/Sys/PetscErrorCode.html">PetscErrorCode</a></span><span class="w"> </span><span class="p">(</span><span class="o">*</span><span class="n">dot</span><span class="p">)(</span><span class="n"><a href="../manualpages/Vec/Vec.html">Vec</a></span><span class="p">,</span><span class="n"><a href="../manualpages/Vec/Vec.html">Vec</a></span><span class="p">,</span><span class="n"><a href="../manualpages/Sys/PetscScalar.html">PetscScalar</a></span><span class="o">*</span><span class="p">);</span><span class="w"> </span><span class="cm">/* z = x^H * y */</span>
<span class="w"> </span><span class="n"><a href="../manualpages/Sys/PetscErrorCode.html">PetscErrorCode</a></span><span class="w"> </span><span class="p">(</span><span class="o">*</span><span class="n">mdot</span><span class="p">)(</span><span class="n"><a href="../manualpages/Vec/Vec.html">Vec</a></span><span class="p">,</span><span class="n"><a href="../manualpages/Sys/PetscInt.html">PetscInt</a></span><span class="p">,</span><span class="k">const</span><span class="w"> </span><span class="n"><a href="../manualpages/Vec/Vec.html">Vec</a></span><span class="p">[],</span><span class="n"><a href="../manualpages/Sys/PetscScalar.html">PetscScalar</a></span><span class="o">*</span><span class="p">);</span><span class="w"> </span><span class="cm">/* z[j] = x dot y[j] */</span>
<span class="w"> </span><span class="n"><a href="../manualpages/Sys/PetscErrorCode.html">PetscErrorCode</a></span><span class="w"> </span><span class="p">(</span><span class="o">*</span><span class="n">norm</span><span class="p">)(</span><span class="n"><a href="../manualpages/Vec/Vec.html">Vec</a></span><span class="p">,</span><span class="n"><a href="../manualpages/Vec/NormType.html">NormType</a></span><span class="p">,</span><span class="n"><a href="../manualpages/Sys/PetscReal.html">PetscReal</a></span><span class="o">*</span><span class="p">);</span><span class="w"> </span><span class="cm">/* z = sqrt(x^H * x) */</span>
<span class="w"> </span><span class="n"><a href="../manualpages/Sys/PetscErrorCode.html">PetscErrorCode</a></span><span class="w"> </span><span class="p">(</span><span class="o">*</span><span class="n">tdot</span><span class="p">)(</span><span class="n"><a href="../manualpages/Vec/Vec.html">Vec</a></span><span class="p">,</span><span class="n"><a href="../manualpages/Vec/Vec.html">Vec</a></span><span class="p">,</span><span class="n"><a href="../manualpages/Sys/PetscScalar.html">PetscScalar</a></span><span class="o">*</span><span class="p">);</span><span class="w"> </span><span class="cm">/* x'*y */</span>
<span class="w"> </span><span class="n"><a href="../manualpages/Sys/PetscErrorCode.html">PetscErrorCode</a></span><span class="w"> </span><span class="p">(</span><span class="o">*</span><span class="n">mtdot</span><span class="p">)(</span><span class="n"><a href="../manualpages/Vec/Vec.html">Vec</a></span><span class="p">,</span><span class="n"><a href="../manualpages/Sys/PetscInt.html">PetscInt</a></span><span class="p">,</span><span class="k">const</span><span class="w"> </span><span class="n"><a href="../manualpages/Vec/Vec.html">Vec</a></span><span class="p">[],</span><span class="n"><a href="../manualpages/Sys/PetscScalar.html">PetscScalar</a></span><span class="o">*</span><span class="p">);</span><span class="cm">/* z[j] = x dot y[j] */</span>
<span class="w"> </span><span class="n"><a href="../manualpages/Sys/PetscErrorCode.html">PetscErrorCode</a></span><span class="w"> </span><span class="p">(</span><span class="o">*</span><span class="n">scale</span><span class="p">)(</span><span class="n"><a href="../manualpages/Vec/Vec.html">Vec</a></span><span class="p">,</span><span class="n"><a href="../manualpages/Sys/PetscScalar.html">PetscScalar</a></span><span class="p">);</span><span class="w"> </span><span class="cm">/* x = alpha * x */</span>
<span class="w"> </span><span class="n"><a href="../manualpages/Sys/PetscErrorCode.html">PetscErrorCode</a></span><span class="w"> </span><span class="p">(</span><span class="o">*</span><span class="n">copy</span><span class="p">)(</span><span class="n"><a href="../manualpages/Vec/Vec.html">Vec</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="cm">/* y = x */</span>
<span class="w"> </span><span class="n"><a href="../manualpages/Sys/PetscErrorCode.html">PetscErrorCode</a></span><span class="w"> </span><span class="p">(</span><span class="o">*</span><span class="n">set</span><span class="p">)(</span><span class="n"><a href="../manualpages/Vec/Vec.html">Vec</a></span><span class="p">,</span><span class="n"><a href="../manualpages/Sys/PetscScalar.html">PetscScalar</a></span><span class="p">);</span><span class="w"> </span><span class="cm">/* y = alpha */</span>
<span class="w"> </span><span class="n"><a href="../manualpages/Sys/PetscErrorCode.html">PetscErrorCode</a></span><span class="w"> </span><span class="p">(</span><span class="o">*</span><span class="n">swap</span><span class="p">)(</span><span class="n"><a href="../manualpages/Vec/Vec.html">Vec</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="cm">/* exchange x and y */</span>
<span class="w"> </span><span class="n"><a href="../manualpages/Sys/PetscErrorCode.html">PetscErrorCode</a></span><span class="w"> </span><span class="p">(</span><span class="o">*</span><span class="n">axpy</span><span class="p">)(</span><span class="n"><a href="../manualpages/Vec/Vec.html">Vec</a></span><span class="p">,</span><span class="n"><a href="../manualpages/Sys/PetscScalar.html">PetscScalar</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="cm">/* y = y + alpha * x */</span>
<span class="w"> </span><span class="n"><a href="../manualpages/Sys/PetscErrorCode.html">PetscErrorCode</a></span><span class="w"> </span><span class="p">(</span><span class="o">*</span><span class="n">axpby</span><span class="p">)(</span><span class="n"><a href="../manualpages/Vec/Vec.html">Vec</a></span><span class="p">,</span><span class="n"><a href="../manualpages/Sys/PetscScalar.html">PetscScalar</a></span><span class="p">,</span><span class="n"><a href="../manualpages/Sys/PetscScalar.html">PetscScalar</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="cm">/* y = alpha * x + beta * y*/</span>
<span class="w"> </span><span class="n"><a href="../manualpages/Sys/PetscErrorCode.html">PetscErrorCode</a></span><span class="w"> </span><span class="p">(</span><span class="o">*</span><span class="n">maxpy</span><span class="p">)(</span><span class="n"><a href="../manualpages/Vec/Vec.html">Vec</a></span><span class="p">,</span><span class="n"><a href="../manualpages/Sys/PetscInt.html">PetscInt</a></span><span class="p">,</span><span class="k">const</span><span class="w"> </span><span class="n"><a href="../manualpages/Sys/PetscScalar.html">PetscScalar</a></span><span class="o">*</span><span class="p">,</span><span class="n"><a href="../manualpages/Vec/Vec.html">Vec</a></span><span class="o">*</span><span class="p">);</span><span class="w"> </span><span class="cm">/* y = y + alpha[j] x[j] */</span>
<span class="w"> </span><span class="p">...</span><span class="w"> </span><span class="p">(</span><span class="n">AND</span><span class="w"> </span><span class="n">SO</span><span class="w"> </span><span class="n">ON</span><span class="p">)</span><span class="w"> </span><span class="p">...</span>
<span class="p">};</span>
</pre></div>
</div>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="k">struct</span><span class="w"> </span><span class="nc">_p_Vec</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n"><a href="../manualpages/Sys/PetscClassId.html">PetscClassId</a></span><span class="w"> </span><span class="n">classid</span><span class="p">;</span>
<span class="w"> </span><span class="n">PetscOps</span><span class="w"> </span><span class="o">*</span><span class="n">bops</span><span class="p">;</span>
<span class="w"> </span><span class="n">VecOps</span><span class="w"> </span><span class="o">*</span><span class="n">ops</span><span class="p">;</span>
<span class="w"> </span><span class="n"><a href="../manualpages/Sys/MPI_Comm.html">MPI_Comm</a></span><span class="w"> </span><span class="n">comm</span><span class="p">;</span>
<span class="w"> </span><span class="n"><a href="../manualpages/Sys/PetscLogDouble.html">PetscLogDouble</a></span><span class="w"> </span><span class="n">flops</span><span class="p">,</span><span class="n">time</span><span class="p">,</span><span class="n">mem</span><span class="p">;</span>
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">id</span><span class="p">;</span>
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">refct</span><span class="p">;</span>
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">tag</span><span class="p">;</span>
<span class="w"> </span><span class="n">DLList</span><span class="w"> </span><span class="n">qlist</span><span class="p">;</span>
<span class="w"> </span><span class="n">OList</span><span class="w"> </span><span class="n">olist</span><span class="p">;</span>
<span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">type_name</span><span class="p">;</span>
<span class="w"> </span><span class="n"><a href="../manualpages/Sys/PetscObject.html">PetscObject</a></span><span class="w"> </span><span class="n">parent</span><span class="p">;</span>
<span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">name</span><span class="p">;</span>
<span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">prefix</span><span class="p">;</span>
<span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="o">**</span><span class="n">fortran_func_pointers</span><span class="p">;</span>
<span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="o">*</span><span class="n">data</span><span class="p">;</span><span class="w"> </span><span class="cm">/* implementation-specific data */</span>
<span class="w"> </span><span class="n"><a href="../manualpages/IS/PetscLayout.html">PetscLayout</a></span><span class="w"> </span><span class="n">map</span><span class="p">;</span>
<span class="w"> </span><span class="n"><a href="../manualpages/IS/ISLocalToGlobalMapping.html">ISLocalToGlobalMapping</a></span><span class="w"> </span><span class="n">mapping</span><span class="p">;</span><span class="w"> </span><span class="cm">/* mapping used in <a href="../manualpages/Vec/VecSetValuesLocal.html">VecSetValuesLocal</a>() */</span>
<span class="p">};</span>
</pre></div>
</div>
<p>Each PETSc object begins with a <code class="docutils notranslate"><span class="pre"><a href="../manualpages/Sys/PetscClassId.html">PetscClassId</a></span></code>, which is used for
error checking. Each different class of objects has its value for
<code class="docutils notranslate"><span class="pre">classid</span></code>; these are used to distinguish between classes. When a new
class is created you need to call</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n"><a href="../manualpages/Log/PetscClassIdRegister.html">PetscClassIdRegister</a></span><span class="p">(</span><span class="k">const</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">classname</span><span class="p">,</span><span class="n"><a href="../manualpages/Sys/PetscClassId.html">PetscClassId</a></span><span class="w"> </span><span class="o">*</span><span class="n">classid</span><span class="p">);</span>
</pre></div>
</div>
<p>For example,</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n"><a href="../manualpages/Log/PetscClassIdRegister.html">PetscClassIdRegister</a></span><span class="p">(</span><span class="s">"index set"</span><span class="p">,</span><span class="o">&</span><span class="n">IS_CLASSID</span><span class="p">);</span>
</pre></div>
</div>
<p>you can verify that an object is valid of a particular class with
<code class="docutils notranslate"><span class="pre">PetscValidHeaderSpecific</span></code>, for example,</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">PetscValidHeaderSpecific</span><span class="p">(</span><span class="n">x</span><span class="p">,</span><span class="n">VEC_CLASSID</span><span class="p">,</span><span class="mi">1</span><span class="p">);</span>
</pre></div>
</div>
<p>The third argument to this macro indicates the position in the calling
sequence of the function the object was passed in. This is to generate
more complete error messages.</p>
<p>To check for an object of any type, use</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">PetscValidHeader</span><span class="p">(</span><span class="n">x</span><span class="p">,</span><span class="mi">1</span><span class="p">);</span>
</pre></div>
</div>
<p>The <code class="docutils notranslate"><span class="pre">obj->ops</span></code> functions provide implementations of the standard methods of the object class. Each type
of the class may have different function pointers in the array. Subtypes sometimes replace some of the
function pointers of the parent, so they play the role of virtual methods in C++.</p>
<p>PETSc code that calls these function pointers should be done via</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n"><a href="../manualpages/Sys/PetscUseTypeMethod.html">PetscUseTypeMethod</a></span><span class="p">(</span><span class="n">obj</span><span class="p">,</span><span class="n">method</span><span class="p">,</span><span class="n">other</span><span class="w"> </span><span class="n">arguments</span><span class="p">);</span>
<span class="n"><a href="../manualpages/Sys/PetscTryTypeMethod.html">PetscTryTypeMethod</a></span><span class="p">(</span><span class="n">obj</span><span class="p">,</span><span class="n">method</span><span class="p">,</span><span class="n">other</span><span class="w"> </span><span class="n">arguments</span><span class="p">);</span>
</pre></div>
</div>
<p>For example,</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n"><a href="../manualpages/Sys/PetscErrorCode.html">PetscErrorCode</a></span><span class="w"> </span><span class="nf">XXXOp</span><span class="p">(</span><span class="n">XXX</span><span class="w"> </span><span class="n">x</span><span class="p">,</span><span class="n">YYY</span><span class="w"> </span><span class="n">y</span><span class="p">)</span>
<span class="p">{</span>
<span class="w"> </span><span class="n"><a href="../manualpages/Sys/PetscFunctionBegin.html">PetscFunctionBegin</a></span><span class="p">;</span>
<span class="w"> </span><span class="n"><a href="../manualpages/Sys/PetscUseTypeMethod.html">PetscUseTypeMethod</a></span><span class="p">(</span><span class="n">x</span><span class="p">,</span><span class="n">op</span><span class="p">,</span><span class="n">y</span><span class="p">);</span>
<span class="w"> </span><span class="n"><a href="../manualpages/Sys/PetscFunctionReturn.html">PetscFunctionReturn</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Sys/PetscErrorCode.html">PETSC_SUCCESS</a></span><span class="p">);</span>
<span class="p">}</span>
</pre></div>
</div>
<p>The <code class="docutils notranslate"><span class="pre">Try</span></code> variant skips the function call if the method has not been set while the <code class="docutils notranslate"><span class="pre">Use</span></code> version generates an error in that case.</p>
<p>See also, <code class="docutils notranslate"><span class="pre"><a href="../manualpages/Sys/PetscUseMethod.html">PetscUseMethod</a>()</span></code>, and <code class="docutils notranslate"><span class="pre"><a href="../manualpages/Sys/PetscTryMethod.html">PetscTryMethod</a>()</span></code>.</p>
</section>
<section id="common-object-functions">
<h2>Common Object Functions<a class="headerlink" href="#common-object-functions" title="Link to this heading">#</a></h2>
<p>Several routines are provided for manipulating data within the header.
These include the specific functions in the PETSc common function table.
The function pointers are not called directly; rather you should call
<code class="docutils notranslate"><span class="pre">PetscObjectFunctionName()</span></code>, where <code class="docutils notranslate"><span class="pre">FunctionName</span></code> is one of the
functions listed below with the first letter of each word capitalized.</p>
<p><code class="docutils notranslate"><span class="pre"><a href="../manualpages/Sys/PetscObjectGetComm.html">PetscObjectGetComm</a>()</span></code> calls the <code class="docutils notranslate"><span class="pre">getcomm(<a href="../manualpages/Sys/PetscObject.html">PetscObject</a>,<a href="../manualpages/Sys/MPI_Comm.html">MPI_Comm</a>*)</span></code> function point which obtains the MPI communicator
associated with this object.</p>
<p><code class="docutils notranslate"><span class="pre"><a href="../manualpages/Sys/PetscObjectView.html">PetscObjectView</a>()</span></code> calls the <code class="docutils notranslate"><span class="pre">view(<a href="../manualpages/Sys/PetscObject.html">PetscObject</a>,<a href="../manualpages/Viewer/PetscViewer.html">PetscViewer</a>)</span></code> function point which allows you to store or visualize the
data inside an object. If the <code class="docutils notranslate"><span class="pre"><a href="../manualpages/Viewer/PetscViewer.html">PetscViewer</a></span></code> is <code class="docutils notranslate"><span class="pre">NULL</span></code>, then it should cause the
object to print information on the object to <code class="docutils notranslate"><span class="pre">stdout</span></code>.</p>
<p><code class="docutils notranslate"><span class="pre"><a href="../manualpages/Sys/PetscObjectDestroy.html">PetscObjectDestroy</a>()</span></code> calls the <code class="docutils notranslate"><span class="pre">destroy(<a href="../manualpages/Sys/PetscObject.html">PetscObject</a>)</span></code> function pointer which causes the reference count of the object to be
decreased by one or the object to be destroyed and all memory used by
the object to be freed when the reference count drops to zero. If the
object has any other objects composed with it, the <code class="docutils notranslate"><span class="pre"><a href="../manualpages/Sys/PetscObjectDestroy.html">PetscObjectDestroy</a>()</span></code> function is called on them.</p>
<p><code class="docutils notranslate"><span class="pre"><a href="../manualpages/Sys/PetscObjectCompose.html">PetscObjectCompose</a>()</span></code> calls the <code class="docutils notranslate"><span class="pre">compose(<a href="../manualpages/Sys/PetscObject.html">PetscObject</a>,const</span> <span class="pre">char</span> <span class="pre">*name,<a href="../manualpages/Sys/PetscObject.html">PetscObject</a>)</span></code> function pointer which associates the
second object with the first object and increases the reference count of
the second object. If an object with the same name was previously
composed, that object is dereferenced and replaced with the new object.
If the second object is <code class="docutils notranslate"><span class="pre">NULL</span></code> and an object with the same name has
already been composed, that object is dereferenced (the <code class="docutils notranslate"><span class="pre"><a href="../manualpages/Sys/PetscObjectDestroy.html">PetscObjectDestroy</a>()</span></code>
function is called on it, and that object is removed from the first
object). This is a way to remove, by name, an object that was previously
composed.</p>
<p><code class="docutils notranslate"><span class="pre"><a href="../manualpages/Sys/PetscObjectQuery.html">PetscObjectQuery</a>()</span></code> calls the <code class="docutils notranslate"><span class="pre">query(<a href="../manualpages/Sys/PetscObject.html">PetscObject</a>,const</span> <span class="pre">char</span> <span class="pre">*name,<a href="../manualpages/Sys/PetscObject.html">PetscObject</a>*)</span></code> function pointer which retrieves an object
that was previously composed with the first object via
<code class="docutils notranslate"><span class="pre"><a href="../manualpages/Sys/PetscObjectCompose.html">PetscObjectCompose</a>()</span></code>. It retrieves a <code class="docutils notranslate"><span class="pre">NULL</span></code> if no object with that
name was previously composed.</p>
<p><code class="docutils notranslate"><span class="pre"><a href="../manualpages/Sys/PetscObjectComposeFunction.html">PetscObjectComposeFunction</a>()</span></code> calls the <code class="docutils notranslate"><span class="pre">composefunction(<a href="../manualpages/Sys/PetscObject.html">PetscObject</a>,const</span> <span class="pre">char</span> <span class="pre">*name,void</span> <span class="pre">*func)</span></code> function pointer which associates
a function pointer with an object. If the object already had a composed
function with the same name, the old one is replaced. If <code class="docutils notranslate"><span class="pre">func</span></code> is
<code class="docutils notranslate"><span class="pre">NULL</span></code>, the existing function is removed from the object. The string
<code class="docutils notranslate"><span class="pre">name</span></code> is the character string name of the function.</p>
<p>For example, <code class="docutils notranslate"><span class="pre">fname</span></code> may be <code class="docutils notranslate"><span class="pre">PCCreate_LU</span></code>.</p>
<p><code class="docutils notranslate"><span class="pre"><a href="../manualpages/Sys/PetscObjectQueryFunction.html">PetscObjectQueryFunction</a>()</span></code> calls the <code class="docutils notranslate"><span class="pre">queryfunction(<a href="../manualpages/Sys/PetscObject.html">PetscObject</a>,const</span> <span class="pre">char</span> <span class="pre">*name,void</span> <span class="pre">**func)</span></code> function pointer which retrieves a
function pointer that was associated with the object via
<code class="docutils notranslate"><span class="pre"><a href="../manualpages/Sys/PetscObjectComposeFunction.html">PetscObjectComposeFunction</a>()</span></code>. If dynamic libraries are used, the
function is loaded into memory at this time (if it has not been
previously loaded), not when the <code class="docutils notranslate"><span class="pre"><a href="../manualpages/Sys/PetscObjectComposeFunction.html">PetscObjectComposeFunction</a>()</span></code> routine was
called.</p>
<p>Since the object composition allows one to compose PETSc objects
with PETSc objects, PETSc provides the
convenience object <code class="docutils notranslate"><span class="pre"><a href="../manualpages/Sys/PetscContainer.html">PetscContainer</a></span></code>, created with the routine
<code class="docutils notranslate"><span class="pre"><a href="../manualpages/Sys/PetscContainerCreate.html">PetscContainerCreate</a>(<a href="../manualpages/Sys/MPI_Comm.html">MPI_Comm</a>,<a href="../manualpages/Sys/PetscContainer.html">PetscContainer</a>*)</span></code>, to allow wrapping any
kind of data into a PETSc object that can then be composed with a PETSc
object. One can also use <code class="docutils notranslate"><span class="pre"><a href="../manualpages/Sys/PetscObjectContainerCompose.html">PetscObjectContainerCompose</a>()</span></code> and <code class="docutils notranslate"><span class="pre"><a href="../manualpages/Sys/PetscObjectContainerQuery.html">PetscObjectContainerQuery</a>()</span></code> to compose
arbitrary pointers with a PETSc object.</p>
</section>
<section id="object-function-implementation">
<h2>Object Function Implementation<a class="headerlink" href="#object-function-implementation" title="Link to this heading">#</a></h2>
<p>This section discusses how PETSc implements the <code class="docutils notranslate"><span class="pre">compose()</span></code>,
<code class="docutils notranslate"><span class="pre">query()</span></code>, <code class="docutils notranslate"><span class="pre">composefunction()</span></code>, and <code class="docutils notranslate"><span class="pre">queryfunction()</span></code> functions
for its object implementations. Other PETSc-compatible class
implementations are free to manage these functions in any manner; but
unless there is a specific reason, they should use the PETSc defaults so
that the library writer does not have to “reinvent the wheel.”</p>
<section id="compose-and-query-objects">
<h3>Compose and Query Objects<a class="headerlink" href="#compose-and-query-objects" title="Link to this heading">#</a></h3>
<p>In
<a href="../src/sys/objects/olist.c.html">src/sys/objects/olist.c</a>
PETSc defines a C <code class="docutils notranslate"><span class="pre">struct</span></code></p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="k">typedef</span><span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="nc">_PetscObjectList</span><span class="o">*</span><span class="w"> </span><span class="n"><a href="../manualpages/Sys/PetscObjectList.html">PetscObjectList</a></span><span class="p">;</span>
<span class="k">struct</span><span class="w"> </span><span class="nc">_PetscObjectList</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="n">name</span><span class="p">[</span><span class="mi">128</span><span class="p">];</span>
<span class="w"> </span><span class="n"><a href="../manualpages/Sys/PetscObject.html">PetscObject</a></span><span class="w"> </span><span class="n">obj</span><span class="p">;</span>
<span class="w"> </span><span class="n"><a href="../manualpages/Sys/PetscObjectList.html">PetscObjectList</a></span><span class="w"> </span><span class="n">next</span><span class="p">;</span>
<span class="p">};</span>
</pre></div>
</div>
<p>from which linked lists of composed objects may be constructed. The
routines to manipulate these elementary objects are</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="kt">int</span><span class="w"> </span><span class="nf"><a href="../manualpages/Sys/PetscObjectListAdd.html">PetscObjectListAdd</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Sys/PetscObjectList.html">PetscObjectList</a></span><span class="w"> </span><span class="o">*</span><span class="n">fl</span><span class="p">,</span><span class="k">const</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">name</span><span class="p">,</span><span class="n"><a href="../manualpages/Sys/PetscObject.html">PetscObject</a></span><span class="w"> </span><span class="n">obj</span><span class="p">);</span>
<span class="kt">int</span><span class="w"> </span><span class="nf"><a href="../manualpages/Sys/PetscObjectListDestroy.html">PetscObjectListDestroy</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Sys/PetscObjectList.html">PetscObjectList</a></span><span class="w"> </span><span class="o">*</span><span class="n">fl</span><span class="p">);</span>
<span class="kt">int</span><span class="w"> </span><span class="nf"><a href="../manualpages/Sys/PetscObjectListFind.html">PetscObjectListFind</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Sys/PetscObjectList.html">PetscObjectList</a></span><span class="w"> </span><span class="n">fl</span><span class="p">,</span><span class="k">const</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">name</span><span class="p">,</span><span class="n"><a href="../manualpages/Sys/PetscObject.html">PetscObject</a></span><span class="w"> </span><span class="o">*</span><span class="n">obj</span><span class="p">)</span>
<span class="kt">int</span><span class="w"> </span><span class="n"><a href="../manualpages/Sys/PetscObjectListDuplicate.html">PetscObjectListDuplicate</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Sys/PetscObjectList.html">PetscObjectList</a></span><span class="w"> </span><span class="n">fl</span><span class="p">,</span><span class="n"><a href="../manualpages/Sys/PetscObjectList.html">PetscObjectList</a></span><span class="w"> </span><span class="o">*</span><span class="n">nl</span><span class="p">);</span>
</pre></div>
</div>
<p>The function <code class="docutils notranslate"><span class="pre"><a href="../manualpages/Sys/PetscObjectListAdd.html">PetscObjectListAdd</a>()</span></code> will create the initial
PetscObjectList if the argument <code class="docutils notranslate"><span class="pre">fl</span></code> points to a NULL.</p>
<p>The PETSc object <code class="docutils notranslate"><span class="pre">compose()</span></code> and <code class="docutils notranslate"><span class="pre">query()</span></code> functions are as follows
(defined in
<a href="../src/sys/objects/inherit.c.html">src/sys/objects/inherit.c</a></p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n"><a href="../manualpages/Sys/PetscErrorCode.html">PetscErrorCode</a></span><span class="w"> </span><span class="nf">PetscObjectCompose_Petsc</span><span class="p">(</span><span class="n"><a href="../manualpages/Sys/PetscObject.html">PetscObject</a></span><span class="w"> </span><span class="n">obj</span><span class="p">,</span><span class="k">const</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">name</span><span class="p">,</span><span class="n"><a href="../manualpages/Sys/PetscObject.html">PetscObject</a></span><span class="w"> </span><span class="n">ptr</span><span class="p">)</span>
<span class="p">{</span>
<span class="w"> </span><span class="n"><a href="../manualpages/Sys/PetscFunctionBegin.html">PetscFunctionBegin</a></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/Sys/PetscObjectListAdd.html">PetscObjectListAdd</a></span><span class="p">(</span><span class="o">&</span><span class="n">obj</span><span class="o">-></span><span class="n">olist</span><span class="p">,</span><span class="n">name</span><span class="p">,</span><span class="n">ptr</span><span class="p">));</span>
<span class="w"> </span><span class="n"><a href="../manualpages/Sys/PetscFunctionReturn.html">PetscFunctionReturn</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Sys/PetscErrorCode.html">PETSC_SUCCESS</a></span><span class="p">);</span>
<span class="p">}</span>
<span class="n"><a href="../manualpages/Sys/PetscErrorCode.html">PetscErrorCode</a></span><span class="w"> </span><span class="nf">PetscObjectQuery_Petsc</span><span class="p">(</span><span class="n"><a href="../manualpages/Sys/PetscObject.html">PetscObject</a></span><span class="w"> </span><span class="n">obj</span><span class="p">,</span><span class="k">const</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">name</span><span class="p">,</span><span class="n"><a href="../manualpages/Sys/PetscObject.html">PetscObject</a></span><span class="w"> </span><span class="o">*</span><span class="n">ptr</span><span class="p">)</span>
<span class="p">{</span>
<span class="w"> </span><span class="n"><a href="../manualpages/Sys/PetscFunctionBegin.html">PetscFunctionBegin</a></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/Sys/PetscObjectListFind.html">PetscObjectListFind</a></span><span class="p">(</span><span class="n">obj</span><span class="o">-></span><span class="n">olist</span><span class="p">,</span><span class="n">name</span><span class="p">,</span><span class="n">ptr</span><span class="p">));</span>
<span class="w"> </span><span class="n"><a href="../manualpages/Sys/PetscFunctionReturn.html">PetscFunctionReturn</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Sys/PetscErrorCode.html">PETSC_SUCCESS</a></span><span class="p">);</span>
<span class="p">}</span>
</pre></div>
</div>
</section>
<section id="compose-and-query-functions">
<h3>Compose and Query Functions<a class="headerlink" href="#compose-and-query-functions" title="Link to this heading">#</a></h3>
<p>PETSc allows you to compose functions by specifying a name and function
pointer. In
<a href="../src/sys/dll/reg.c.html">src/sys/dll/reg.c</a>
PETSc defines the following linked list structure.</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="k">struct</span><span class="w"> </span><span class="nc">_n_PetscFunctionList</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="p">(</span><span class="o">*</span><span class="n">routine</span><span class="p">)(</span><span class="kt">void</span><span class="p">);</span><span class="w"> </span><span class="cm">/* the routine */</span>
<span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">name</span><span class="p">;</span><span class="w"> </span><span class="cm">/* string to identify routine */</span>
<span class="w"> </span><span class="n"><a href="../manualpages/Sys/PetscFunctionList.html">PetscFunctionList</a></span><span class="w"> </span><span class="n">next</span><span class="p">;</span><span class="w"> </span><span class="cm">/* next pointer */</span>
<span class="w"> </span><span class="n"><a href="../manualpages/Sys/PetscFunctionList.html">PetscFunctionList</a></span><span class="w"> </span><span class="n">next_list</span><span class="p">;</span><span class="w"> </span><span class="cm">/* used to maintain list of all lists for freeing */</span>
<span class="p">};</span>
</pre></div>
</div>
<p>Each PETSc object contains a <code class="docutils notranslate"><span class="pre"><a href="../manualpages/Sys/PetscFunctionList.html">PetscFunctionList</a></span></code> object. The
<code class="docutils notranslate"><span class="pre">composefunction()</span></code> and <code class="docutils notranslate"><span class="pre">queryfunction()</span></code> are given by the
following.</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n"><a href="../manualpages/Sys/PetscErrorCode.html">PetscErrorCode</a></span><span class="w"> </span><span class="nf">PetscObjectComposeFunction_Petsc</span><span class="p">(</span><span class="n"><a href="../manualpages/Sys/PetscObject.html">PetscObject</a></span><span class="w"> </span><span class="n">obj</span><span class="p">,</span><span class="k">const</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">name</span><span class="p">,</span><span class="kt">void</span><span class="w"> </span><span class="o">*</span><span class="n">ptr</span><span class="p">)</span>
<span class="p">{</span>
<span class="w"> </span><span class="n"><a href="../manualpages/Sys/PetscFunctionBegin.html">PetscFunctionBegin</a></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/Sys/PetscFunctionListAdd.html">PetscFunctionListAdd</a></span><span class="p">(</span><span class="o">&</span><span class="n">obj</span><span class="o">-></span><span class="n">qlist</span><span class="p">,</span><span class="n">name</span><span class="p">,</span><span class="n">fname</span><span class="p">,</span><span class="n">ptr</span><span class="p">));</span>
<span class="w"> </span><span class="n"><a href="../manualpages/Sys/PetscFunctionReturn.html">PetscFunctionReturn</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Sys/PetscErrorCode.html">PETSC_SUCCESS</a></span><span class="p">);</span>
<span class="p">}</span>
<span class="n"><a href="../manualpages/Sys/PetscErrorCode.html">PetscErrorCode</a></span><span class="w"> </span><span class="nf">PetscObjectQueryFunction_Petsc</span><span class="p">(</span><span class="n"><a href="../manualpages/Sys/PetscObject.html">PetscObject</a></span><span class="w"> </span><span class="n">obj</span><span class="p">,</span><span class="k">const</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">name</span><span class="p">,</span><span class="kt">void</span><span class="w"> </span><span class="p">(</span><span class="o">**</span><span class="n">ptr</span><span class="p">)(</span><span class="kt">void</span><span class="p">))</span>
<span class="p">{</span>
<span class="w"> </span><span class="n"><a href="../manualpages/Sys/PetscFunctionBegin.html">PetscFunctionBegin</a></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/Sys/PetscFunctionListFind.html">PetscFunctionListFind</a></span><span class="p">(</span><span class="n">obj</span><span class="o">-></span><span class="n">qlist</span><span class="p">,</span><span class="n">name</span><span class="p">,</span><span class="n">ptr</span><span class="p">));</span>
<span class="w"> </span><span class="n"><a href="../manualpages/Sys/PetscFunctionReturn.html">PetscFunctionReturn</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Sys/PetscErrorCode.html">PETSC_SUCCESS</a></span><span class="p">);</span>
<span class="p">}</span>
</pre></div>
</div>
<p>In addition to using the <code class="docutils notranslate"><span class="pre"><a href="../manualpages/Sys/PetscFunctionList.html">PetscFunctionList</a></span></code> mechanism to compose
functions into PETSc objects, it is also used to allow registration of
new class implementations; for example, new preconditioners.</p>
<p>PETSc code that calls composed functions should be done via</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n"><a href="../manualpages/Sys/PetscUseMethod.html">PetscUseMethod</a></span><span class="p">(</span><span class="n">obj</span><span class="p">,</span><span class="s">"method"</span><span class="p">,(</span><span class="n">Argument</span><span class="w"> </span><span class="n">types</span><span class="p">),(</span><span class="n">argument</span><span class="w"> </span><span class="n">variables</span><span class="p">));</span>
<span class="n"><a href="../manualpages/Sys/PetscTryMethod.html">PetscTryMethod</a></span><span class="p">(</span><span class="n">obj</span><span class="p">,</span><span class="s">"method"</span><span class="p">,(</span><span class="n">Argument</span><span class="w"> </span><span class="n">types</span><span class="p">),(</span><span class="n">argument</span><span class="w"> </span><span class="n">variables</span><span class="p">));</span>
</pre></div>
</div>
<p>For example,</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n"><a href="../manualpages/Sys/PetscErrorCode.html">PetscErrorCode</a></span><span class="w"> </span><span class="nf"><a href="../manualpages/KSP/KSPGMRESSetRestart.html">KSPGMRESSetRestart</a></span><span class="p">(</span><span class="n"><a href="../manualpages/KSP/KSP.html">KSP</a></span><span class="w"> </span><span class="n">ksp</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">restart</span><span class="p">)</span>
<span class="p">{</span>
<span class="w"> </span><span class="n"><a href="../manualpages/Sys/PetscFunctionBegin.html">PetscFunctionBegin</a></span><span class="p">;</span>
<span class="w"> </span><span class="n">PetscValidLogicalCollectiveInt</span><span class="p">(</span><span class="n">ksp</span><span class="p">,</span><span class="n">restart</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/PetscTryMethod.html">PetscTryMethod</a></span><span class="p">(</span><span class="n">ksp</span><span class="p">,</span><span class="s">"KSPGMRESSetRestart_C"</span><span class="p">,(</span><span class="n"><a href="../manualpages/KSP/KSP.html">KSP</a></span><span class="p">,</span><span class="n"><a href="../manualpages/Sys/PetscInt.html">PetscInt</a></span><span class="p">),(</span><span class="n">ksp</span><span class="p">,</span><span class="n">restart</span><span class="p">));</span>
<span class="w"> </span><span class="n"><a href="../manualpages/Sys/PetscFunctionReturn.html">PetscFunctionReturn</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Sys/PetscErrorCode.html">PETSC_SUCCESS</a></span><span class="p">);</span>
<span class="p">}</span>
</pre></div>
</div>
<p>The <code class="docutils notranslate"><span class="pre">Try</span></code> variant skips the function call if the method has not been composed with
the object while the <code class="docutils notranslate"><span class="pre">Use</span></code> version generates an error in that case.
See also, <code class="docutils notranslate"><span class="pre"><a href="../manualpages/Sys/PetscUseTypeMethod.html">PetscUseTypeMethod</a>()</span></code>, and <code class="docutils notranslate"><span class="pre"><a href="../manualpages/Sys/PetscTryTypeMethod.html">PetscTryTypeMethod</a>()</span></code>.</p>
</section>
<section id="simple-petsc-objects">
<h3>Simple PETSc Objects<a class="headerlink" href="#simple-petsc-objects" title="Link to this heading">#</a></h3>
<p>Some simple PETSc objects do not need <code class="docutils notranslate"><span class="pre">PETSCHEADER</span></code> and the associated
functionality. These objects are internally named as <code class="docutils notranslate"><span class="pre">_n_<class></span></code> as
opposed to <code class="docutils notranslate"><span class="pre">_p_<class></span></code>, for example, <code class="docutils notranslate"><span class="pre">_n_PetscFunctionList</span></code> vs <code class="docutils notranslate"><span class="pre">_p_Vec</span></code>.</p>
</section>
</section>
<section id="petsc-packages">
<h2>PETSc Packages<a class="headerlink" href="#petsc-packages" title="Link to this heading">#</a></h2>
<p>The PETSc source code is divided into the following library-level
packages: <code class="docutils notranslate"><span class="pre">Sys</span></code>, <code class="docutils notranslate"><span class="pre"><a href="../manualpages/Vec/Vec.html">Vec</a></span></code>, <code class="docutils notranslate"><span class="pre"><a href="../manualpages/Mat/Mat.html">Mat</a></span></code>, <code class="docutils notranslate"><span class="pre"><a href="../manualpages/DM/DM.html">DM</a></span></code>, <code class="docutils notranslate"><span class="pre"><a href="../manualpages/KSP/KSP.html">KSP</a></span></code>, <code class="docutils notranslate"><span class="pre"><a href="../manualpages/SNES/SNES.html">SNES</a></span></code>, <code class="docutils notranslate"><span class="pre"><a href="../manualpages/TS/TS.html">TS</a></span></code>,
<code class="docutils notranslate"><span class="pre"><a href="../manualpages/Tao/Tao.html">Tao</a></span></code>. Each of these has a directory under the <code class="docutils notranslate"><span class="pre">src</span></code> directory in
the PETSc tree and, optionally, can be compiled into separate libraries.
Each package defines one or more classes; for example, the <code class="docutils notranslate"><span class="pre"><a href="../manualpages/KSP/KSP.html">KSP</a></span></code>
package defines the <code class="docutils notranslate"><span class="pre"><a href="../manualpages/KSP/KSP.html">KSP</a></span></code> and <code class="docutils notranslate"><span class="pre"><a href="../manualpages/PC/PC.html">PC</a></span></code> classes, as well as several
utility classes. In addition, each library-level package may contain
several class-level packages associated with individual classes in the
library-level package. In general, most “important” classes in PETSc
have their own class level package. Each package provides a registration
function <code class="docutils notranslate"><span class="pre">XXXInitializePackage()</span></code>, for example
<code class="docutils notranslate"><span class="pre"><a href="../manualpages/KSP/KSPInitializePackage.html">KSPInitializePackage</a>()</span></code>, which registers all the classes and events
for that package. Each package also registers a finalization routine,
<code class="docutils notranslate"><span class="pre">XXXFinalizePackage()</span></code>, that releases all the resources used in
registering the package, using <code class="docutils notranslate"><span class="pre"><a href="../manualpages/Sys/PetscRegisterFinalize.html">PetscRegisterFinalize</a>()</span></code>. The
registration for each package is performed “on demand” the first time a
class in the package is utilized. This is handled, for example, with
code such as</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n"><a href="../manualpages/Sys/PetscErrorCode.html">PetscErrorCode</a></span><span class="w"> </span><span class="nf"><a href="../manualpages/Vec/VecCreate.html">VecCreate</a></span><span class="p">(</span><span class="n"><a href="../manualpages/Sys/MPI_Comm.html">MPI_Comm</a></span><span class="w"> </span><span class="n">comm</span><span class="p">,</span><span class="w"> </span><span class="n"><a href="../manualpages/Vec/Vec.html">Vec</a></span><span class="w"> </span><span class="o">*</span><span class="n">vec</span><span class="p">)</span>
<span class="p">{</span>
<span class="w"> </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="w"> </span><span class="n"><a href="../manualpages/Sys/PetscFunctionBegin.html">PetscFunctionBegin</a></span><span class="p">;</span>
<span class="w"> </span><span class="n">PetscAssertPointer</span><span class="p">(</span><span class="n">vec</span><span class="p">,</span><span class="mi">2</span><span class="p">);</span>
<span class="w"> </span><span class="o">*</span><span class="n">vec</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nb">NULL</span><span class="p">;</span>
<span class="w"> </span><span class="n"><a href="../manualpages/Vec/VecInitializePackage.html">VecInitializePackage</a></span><span class="p">();</span>
<span class="w"> </span><span class="p">...</span>
</pre></div>
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