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, first, step
 15:   PetscInt, parameter :: n = 10
 16:   IS set
 17:   PetscInt, pointer :: index(:)

 19:   PetscCallA(PetscInitialize(ierr))
 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:     write (6, 30) index(i)
 38:   end do
 39: 20 format('Printing indices directly')
 40: 30 format(i3)
 41:   PetscCallA(ISRestoreIndices(set, index, ierr))

 43: !     Determine information on stride

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

 48:   PetscCallA(ISDestroy(set, ierr))
 49:   PetscCallA(PetscFinalize(ierr))
 50: end

 52: !/*TEST
 53: !
 54: !   test:
 55: !
 56: !TEST*/