petsc-dev 2014-04-16
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Fortran can be used with PETSc in four distinct approaches
   1) classic Fortran 77 style
.#include "finclude/petscXXX.h" to work with material from the XXX component of PETSc
      XXX variablename
     You cannot use this approach if you wish to use the Fortran 90 specific PETSc routines
     which end in F90; such as VecGetArrayF90()

   2) classic Fortran 90 style
.#include "finclude/petscXXX.h" .#include "finclude/petscXXX.h90" to work with material from the XXX component of PETSc
      XXX variablename

   3) Using Fortran modules
.#include "finclude/petscXXXdef.h"
        use petscXXXX
      XXX variablename

   4) Use Fortran modules and Fortran data types for PETSc types
.#include "finclude/petscXXXdef.h"
        use petscXXXX
      type(XXX) variablename
     To use this approach you must ./configure PETSc with the additional
     option --with-fortran-datatypes You cannot use the type(XXX) declaration approach without using Fortran modules

Finally if you absolutely do not want to use any #include you can use either

   3a) skip the #include BUT you cannot use any PETSc data type names like Vec, Mat, PetscInt, PetscErrorCode etc
       and you must declare the variables as integer, for example
       integer variablename

   4a) skip the #include, you use the object types like type(Vec) type(Mat) but cannot use the data type
       names like PetscErrorCode, PetscInt etc. again for those you must use integer

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.

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 MatSetValues() you cannot have something like

     PetscInt row,col
     PetscScalar val
     call MatSetValues(mat,1,row,1,col,val,INSERT_VALUES,ierr)
You must instead have
     PetscInt row(1),col(1)
     PetscScalar val(1)
     call MatSetValues(mat,1,row,1,col,val,INSERT_VALUES,ierr)

See the example src/vec/vec/examples/tutorials/ex20f90.F90 for an example that can use all four approaches

Developer Notes: The finclude/petscXXXdef.h contain all the #defines (would be typedefs in C code) these automatically include their predecessors; for example finclude/petscvecdef.h includes finclude/petscisdef.h

The finclude/petscXXXX.h contain all the parameter statements for that package. These automatically include their finclude/petscXXXdef.h file but DO NOT automatically include their predecessors; for example finclude/petscvec.h does NOT automatically include finclude/petscis.h

The 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(Vec)) when PETSc is ./configure with the --with-fortran-datatypes option.

The 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 VecGetArrayF90).

The finclude/ftn-auto/petscXXX.h90 (not included directly by code) contain interface definitions generated automatically by "make allfortranstubs".

The finclude/petscXXX.h90 includes the custom finclude/ftn-custom/petscXXX.h90 and if ./configure was run with --with-fortran-interfaces it also includes the finclude/ftn-auto/petscXXX.h90 These DO NOT automatically include their predecessors

Index of all Sys routines
Table of Contents for all manual pages
Index of all manual pages src/vec/vec/examples/tutorials/ex20f90.F90.html