1: !
  2: !     Description: Creates an index set based on a stride. Views that
  3: !     index set and then destroys it.
  4: !
  5: !
  6: !     Include petscis.h so we can use PETSc IS objects.
  7: !
  8: #include <petsc/finclude/petscis.h>
  9: program main
 10:   use petscis
 11:   implicit none

 13:   PetscErrorCode ierr
 14:   PetscInt i, n, first, step, val
 15:   IS set
 16:   PetscInt, pointer :: index(:)

 18:   PetscCallA(PetscInitialize(ierr))
 19:   n = 10
 20:   first = 3
 21:   step = 2

 23: !     Create stride index set, starting at 3 with a stride of 2 Note
 24: !     each processor is generating its own index set (in this case they
 25: !     are all identical)

 27:   PetscCallA(ISCreateStride(PETSC_COMM_SELF, n, first, step, set, ierr))
 28:   PetscCallA(ISView(set, PETSC_VIEWER_STDOUT_SELF, ierr))

 30: !     Extract the indices values from the set. Demonstrates how a Fortran
 31: !     code can directly access the array storing a PETSc index set with
 32: !     ISGetIndices().

 34:   PetscCallA(ISGetIndices(set, index, ierr))
 35:   write (6, 20)
 36:   do i = 1, n
 37:     val = index(i)
 38:     write (6, 30) val
 39:   end do
 40: 20 format('Printing indices directly')
 41: 30 format(i3)
 42:   PetscCallA(ISRestoreIndices(set, index, ierr))

 44: !     Determine information on stride

 46:   PetscCallA(ISStrideGetInfo(set, first, step, ierr))
 47:   if (first /= 3 .or. step /= 2) then
 48:     print *, 'Stride info not correct!'
 49:   end if

 51:   PetscCallA(ISDestroy(set, ierr))
 52:   PetscCallA(PetscFinalize(ierr))
 53: end

 55: !/*TEST
 56: !
 57: !   test:
 58: !
 59: !TEST*/