1: static char help[] = "Demonstrates creating a stride index set.\n\n";

  3: /*
  4:   Include petscis.h so we can use PETSc IS objects. Note that this automatically
  5:   includes petscsys.h.
  6: */

  8: #include <petscis.h>
  9: #include <petscviewer.h>

 11: int main(int argc, char **argv)
 12: {
 13:   PetscInt        i, n, first, step;
 14:   IS              set;
 15:   const PetscInt *indices;

 17:   PetscFunctionBeginUser;
 18:   PetscCall(PetscInitialize(&argc, &argv, NULL, help));

 20:   n     = 10;
 21:   first = 3;
 22:   step  = 2;

 24:   /*
 25:     Create stride index set, starting at 3 with a stride of 2
 26:     Note each processor is generating its own index set
 27:     (in this case they are all identical)
 28:   */
 29:   PetscCall(ISCreateStride(PETSC_COMM_SELF, n, first, step, &set));
 30:   PetscCall(ISView(set, PETSC_VIEWER_STDOUT_SELF));

 32:   /*
 33:     Extract indices from set.
 34:   */
 35:   PetscCall(ISGetIndices(set, &indices));
 36:   PetscCall(PetscPrintf(PETSC_COMM_WORLD, "Printing indices directly\n"));
 37:   for (i = 0; i < n; i++) PetscCall(PetscPrintf(PETSC_COMM_WORLD, "%" PetscInt_FMT "\n", indices[i]));

 39:   PetscCall(ISRestoreIndices(set, &indices));

 41:   /*
 42:       Determine information on stride
 43:   */
 44:   PetscCall(ISStrideGetInfo(set, &first, &step));
 45:   PetscCheck(first == 3 && step == 2, PETSC_COMM_SELF, PETSC_ERR_PLIB, "Stride info not correct!");
 46:   PetscCall(ISDestroy(&set));
 47:   PetscCall(PetscFinalize());
 48:   return 0;
 49: }

 51: /*TEST

 53:    test:

 55: TEST*/