1: static char help[] = "Creating a general 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: */
  7: #include <petscis.h>
  8: #include <petscviewer.h>

 10: int main(int argc, char **argv)
 11: {
 12:   PetscInt       *indices, n;
 13:   const PetscInt *nindices;
 14:   PetscMPIInt     rank;
 15:   IS              is;

 17:   PetscFunctionBeginUser;
 18:   PetscCall(PetscInitialize(&argc, &argv, (char *)0, help));
 19:   PetscCallMPI(MPI_Comm_rank(PETSC_COMM_WORLD, &rank));

 21:   /*
 22:      Create an index set with 5 entries. Each processor creates
 23:    its own index set with its own list of integers.
 24:   */
 25:   PetscCall(PetscMalloc1(5, &indices));
 26:   indices[0] = rank + 1;
 27:   indices[1] = rank + 2;
 28:   indices[2] = rank + 3;
 29:   indices[3] = rank + 4;
 30:   indices[4] = rank + 5;
 31:   PetscCall(ISCreateGeneral(PETSC_COMM_SELF, 5, indices, PETSC_COPY_VALUES, &is));
 32:   /*
 33:      Note that ISCreateGeneral() has made a copy of the indices
 34:      so we may (and generally should) free indices[]
 35:   */
 36:   PetscCall(PetscFree(indices));

 38:   /*
 39:      Print the index set to stdout
 40:   */
 41:   PetscCall(ISView(is, PETSC_VIEWER_STDOUT_SELF));

 43:   /*
 44:      Get the number of indices in the set
 45:   */
 46:   PetscCall(ISGetLocalSize(is, &n));

 48:   /*
 49:      Get the indices in the index set
 50:   */
 51:   PetscCall(ISGetIndices(is, &nindices));
 52:   /*
 53:      Now any code that needs access to the list of integers
 54:    has access to it here through indices[].
 55:    */
 56:   PetscCall(PetscPrintf(PETSC_COMM_SELF, "[%d] First index %" PetscInt_FMT "\n", rank, nindices[0]));

 58:   /*
 59:      Once we no longer need access to the indices they should
 60:      returned to the system
 61:   */
 62:   PetscCall(ISRestoreIndices(is, &nindices));

 64:   /*
 65:      One should destroy any PETSc object once one is completely
 66:     done with it.
 67:   */
 68:   PetscCall(ISDestroy(&is));
 69:   PetscCall(PetscFinalize());
 70:   return 0;
 71: }

 73: /*TEST

 75:    test:

 77: TEST*/