Actual source code: ex25.c

  1: static char help[] = "Scatters from a parallel vector to a sequential vector.  In\n\
  2: this case processor zero is as long as the entire parallel vector; rest are zero length.\n\n";

  4: #include <petscvec.h>

  6: int main(int argc, char **argv)
  7: {
  8:   PetscInt    n = 5, N, low, high, iglobal, i;
  9:   PetscMPIInt size, rank;
 10:   PetscScalar value, zero = 0.0;
 11:   Vec         x, y;
 12:   IS          is1, is2;
 13:   VecScatter  ctx;

 15:   PetscFunctionBeginUser;
 16:   PetscCall(PetscInitialize(&argc, &argv, NULL, help));
 17:   PetscCallMPI(MPI_Comm_size(PETSC_COMM_WORLD, &size));
 18:   PetscCallMPI(MPI_Comm_rank(PETSC_COMM_WORLD, &rank));

 20:   /* create two vectors */
 21:   N = size * n;
 22:   PetscCall(VecCreate(PETSC_COMM_WORLD, &y));
 23:   PetscCall(VecSetSizes(y, PETSC_DECIDE, N));
 24:   PetscCall(VecSetFromOptions(y));
 25:   if (rank == 0) {
 26:     PetscCall(VecCreateSeq(PETSC_COMM_SELF, N, &x));
 27:   } else {
 28:     PetscCall(VecCreateSeq(PETSC_COMM_SELF, 0, &x));
 29:   }

 31:   /* create two index sets */
 32:   if (rank == 0) {
 33:     PetscCall(ISCreateStride(PETSC_COMM_SELF, N, 0, 1, &is1));
 34:     PetscCall(ISCreateStride(PETSC_COMM_SELF, N, 0, 1, &is2));
 35:   } else {
 36:     PetscCall(ISCreateStride(PETSC_COMM_SELF, 0, 0, 1, &is1));
 37:     PetscCall(ISCreateStride(PETSC_COMM_SELF, 0, 0, 1, &is2));
 38:   }

 40:   PetscCall(VecSet(x, zero));
 41:   PetscCall(VecGetOwnershipRange(y, &low, &high));
 42:   for (i = 0; i < n; i++) {
 43:     iglobal = i + low;
 44:     value   = (PetscScalar)(i + 10 * rank);
 45:     PetscCall(VecSetValues(y, 1, &iglobal, &value, INSERT_VALUES));
 46:   }
 47:   PetscCall(VecAssemblyBegin(y));
 48:   PetscCall(VecAssemblyEnd(y));
 49:   PetscCall(VecView(y, PETSC_VIEWER_STDOUT_WORLD));

 51:   PetscCall(VecScatterCreate(y, is2, x, is1, &ctx));
 52:   PetscCall(VecScatterBegin(ctx, y, x, ADD_VALUES, SCATTER_FORWARD));
 53:   PetscCall(VecScatterEnd(ctx, y, x, ADD_VALUES, SCATTER_FORWARD));
 54:   PetscCall(VecScatterDestroy(&ctx));

 56:   if (rank == 0) {
 57:     PetscCall(PetscPrintf(PETSC_COMM_SELF, "----\n"));
 58:     PetscCall(VecView(x, PETSC_VIEWER_STDOUT_SELF));
 59:   }

 61:   PetscCall(VecDestroy(&x));
 62:   PetscCall(VecDestroy(&y));
 63:   PetscCall(ISDestroy(&is1));
 64:   PetscCall(ISDestroy(&is2));

 66:   PetscCall(PetscFinalize());
 67:   return 0;
 68: }

 70: /*TEST

 72:    test:
 73:       nsize: 3

 75: TEST*/