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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML3.2 EN">
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<TITLE>UsingFortran</TITLE>
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<div id="version" align=right><b>petsc-3.7.5 2017-01-01</b></div>
<div id="bugreport" align=right><a href="mailto:petsc-maint@mcs.anl.gov?subject=Typo or Error in Documentation &body=Please describe the typo or error in the documentation: petsc-3.7.5 v3.7.5 docs/manualpages/Sys/UsingFortran.html "><small>Report Typos and Errors</small></a></div>
<A NAME="UsingFortran"><H1>UsingFortran</H1></A>
Fortran can be used with PETSc in four distinct approaches
<pre>
1) classic Fortran 77 style
</pre>
.#include "petsc/finclude/petscXXX.h" to work with material from the XXX component of PETSc
</pre>
<pre>
XXX variablename
</pre>
<pre>
You cannot use this approach if you wish to use the Fortran 90 specific PETSc routines
</pre>
<pre>
which end in F90; such as <A HREF="../Vec/VecGetArrayF90.html#VecGetArrayF90">VecGetArrayF90</A>()
</pre>
<pre>
</pre>
<pre>
2) classic Fortran 90 style
</pre>
.#include "petsc/finclude/petscXXX.h"
</pre>
.#include "petsc/finclude/petscXXX.h90" to work with material from the XXX component of PETSc
</pre>
<pre>
XXX variablename
</pre>
<pre>
</pre>
<pre>
3) Using Fortran modules
</pre>
.#include "petsc/finclude/petscXXXdef.h"
</pre>
<pre>
use petscXXXX
</pre>
<pre>
XXX variablename
</pre>
<pre>
</pre>
<pre>
4) Use Fortran modules and Fortran data types for PETSc types
</pre>
.#include "petsc/finclude/petscXXXdef.h"
</pre>
<pre>
use petscXXXX
</pre>
<pre>
type(XXX) variablename
</pre>
<pre>
To use this approach you must ./configure PETSc with the additional
</pre>
<pre>
option --with-fortran-datatypes You cannot use the type(XXX) declaration approach without using Fortran modules
</pre>
<P>
Finally if you absolutely do not want to use any #include you can use either
<P>
<pre>
3a) skip the #include BUT you cannot use any PETSc data type names like <A HREF="../Vec/Vec.html#Vec">Vec</A>, <A HREF="../Mat/Mat.html#Mat">Mat</A>, <A HREF="../Sys/PetscInt.html#PetscInt">PetscInt</A>, <A HREF="../Sys/PetscErrorCode.html#PetscErrorCode">PetscErrorCode</A> etc
</pre>
<pre>
and you must declare the variables as integer, for example
</pre>
<pre>
integer variablename
</pre>
<pre>
</pre>
<pre>
4a) skip the #include, you use the object types like type(<A HREF="../Vec/Vec.html#Vec">Vec</A>) type(<A HREF="../Mat/Mat.html#Mat">Mat</A>) but cannot use the data type
</pre>
<pre>
names like <A HREF="../Sys/PetscErrorCode.html#PetscErrorCode">PetscErrorCode</A>, <A HREF="../Sys/PetscInt.html#PetscInt">PetscInt</A> etc. again for those you must use integer
</pre>
<P>
We recommend either 2 or 3. Approaches 2 and 3 provide type checking for most PETSc function calls; 4 has type checking
for only a few PETSc functions.
<P>
Fortran type checking with interfaces is strick, this means you cannot pass a scalar value when an array value
is expected (even though it is legal Fortran). For example when setting a single value in a matrix with <A HREF="../Mat/MatSetValues.html#MatSetValues">MatSetValues</A>()
you cannot have something like
<pre>
<A HREF="../Sys/PetscInt.html#PetscInt">PetscInt</A> row,col
</pre>
<pre>
<A HREF="../Sys/PetscScalar.html#PetscScalar">PetscScalar</A> val
</pre>
<pre>
...
</pre>
<pre>
call <A HREF="../Mat/MatSetValues.html#MatSetValues">MatSetValues</A>(mat,1,row,1,col,val,<A HREF="../Sys/INSERT_VALUES.html#INSERT_VALUES">INSERT_VALUES</A>,ierr)
</pre>
You must instead have
<pre>
<A HREF="../Sys/PetscInt.html#PetscInt">PetscInt</A> row(1),col(1)
</pre>
<pre>
<A HREF="../Sys/PetscScalar.html#PetscScalar">PetscScalar</A> val(1)
</pre>
<pre>
...
</pre>
<pre>
call <A HREF="../Mat/MatSetValues.html#MatSetValues">MatSetValues</A>(mat,1,row,1,col,val,<A HREF="../Sys/INSERT_VALUES.html#INSERT_VALUES">INSERT_VALUES</A>,ierr)
</pre>
<P>
<P>
See the example src/vec/vec/examples/tutorials/ex20f90.F90 for an example that can use all four approaches
<P>
Developer Notes: The petsc/finclude/petscXXXdef.h contain all the #defines (would be typedefs in C code) these
automatically include their predecessors; for example petsc/finclude/petscvecdef.h includes petsc/finclude/petscisdef.h
<P>
The petsc/finclude/petscXXXX.h contain all the parameter statements for that package. These automatically include
their petsc/finclude/petscXXXdef.h file but DO NOT automatically include their predecessors; for example
petsc/finclude/petscvec.h does NOT automatically include petsc/finclude/petscis.h
<P>
The petsc/finclude/ftn-custom/petscXXXdef.h90 are not intended to be used directly in code, they define the
Fortran data type type(XXX) (for example type(<A HREF="../Vec/Vec.html#Vec">Vec</A>)) when PETSc is ./configure with the --with-fortran-datatypes option.
<P>
The petsc/finclude/ftn-custom/petscXXX.h90 (not included directly by code) contain interface definitions for
the PETSc Fortran stubs that have different bindings then their C version (for example <A HREF="../Vec/VecGetArrayF90.html#VecGetArrayF90">VecGetArrayF90</A>).
<P>
The petsc/finclude/ftn-auto/petscXXX.h90 (not included directly by code) contain interface definitions generated
automatically by "make allfortranstubs".
<P>
The petsc/finclude/petscXXX.h90 includes the custom petsc/finclude/ftn-custom/petscXXX.h90 and if ./configure
was run with --with-fortran-interfaces it also includes the petsc/finclude/ftn-auto/petscXXX.h90 These DO NOT automatically
include their predecessors
<P>
<P>
<P><B><P><B><FONT COLOR="#CC3333">Level:</FONT></B>beginner
<BR><FONT COLOR="#CC3333">Location:</FONT></B><A HREF="../../../include/petscsys.h.html#UsingFortran">include/petscsys.h</A>
<BR><A HREF="./index.html">Index of all Sys routines</A>
<BR><A HREF="../../index.html">Table of Contents for all manual pages</A>
<BR><A HREF="../singleindex.html">Index of all manual pages</A>
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