Actual source code: ex5.c


  2: static char help[] = "Scatters from a parallel vector to a sequential vector.\n\
  3: This does case when we are merely selecting the local part of the\n\
  4: parallel vector.\n\n";

  6: #include <petscvec.h>

  8: int main(int argc, char **argv)
  9: {
 10:   PetscMPIInt size, rank;
 11:   PetscInt    n = 5, i;
 12:   PetscScalar value;
 13:   Vec         x, y;
 14:   IS          is1, is2;
 15:   VecScatter  ctx = 0;

 18:   PetscInitialize(&argc, &argv, (char *)0, help);
 19:   MPI_Comm_size(PETSC_COMM_WORLD, &size);
 20:   MPI_Comm_rank(PETSC_COMM_WORLD, &rank);

 22:   /* create two vectors */
 23:   VecCreate(PETSC_COMM_WORLD, &x);
 24:   VecSetSizes(x, PETSC_DECIDE, size * n);
 25:   VecSetFromOptions(x);
 26:   VecCreateSeq(PETSC_COMM_SELF, n, &y);

 28:   /* create two index sets */
 29:   ISCreateStride(PETSC_COMM_SELF, n, n * rank, 1, &is1);
 30:   ISCreateStride(PETSC_COMM_SELF, n, 0, 1, &is2);

 32:   /* each processor inserts the entire vector */
 33:   /* this is redundant but tests assembly */
 34:   for (i = 0; i < n * size; i++) {
 35:     value = (PetscScalar)i;
 36:     VecSetValues(x, 1, &i, &value, INSERT_VALUES);
 37:   }
 38:   VecAssemblyBegin(x);
 39:   VecAssemblyEnd(x);
 40:   VecView(x, PETSC_VIEWER_STDOUT_WORLD);

 42:   VecScatterCreate(x, is1, y, is2, &ctx);
 43:   VecScatterBegin(ctx, x, y, INSERT_VALUES, SCATTER_FORWARD);
 44:   VecScatterEnd(ctx, x, y, INSERT_VALUES, SCATTER_FORWARD);
 45:   VecScatterDestroy(&ctx);

 47:   if (rank == 0) {
 48:     PetscPrintf(PETSC_COMM_SELF, "----\n");
 49:     VecView(y, PETSC_VIEWER_STDOUT_SELF);
 50:   }

 52:   VecDestroy(&x);
 53:   VecDestroy(&y);
 54:   ISDestroy(&is1);
 55:   ISDestroy(&is2);

 57:   PetscFinalize();
 58:   return 0;
 59: }

 61: /*TEST

 63:      test:
 64:        nsize: 2

 66: TEST*/