Actual source code: ex17.c


  2: static char help[] = "Scatters from a parallel vector to a sequential vector.  In\n\
  3: this case each local vector is as long as the entire parallel vector.\n\n";

  5: #include <petscvec.h>

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

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

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

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

 32:   VecSet(x, zero);
 33:   VecGetOwnershipRange(y, &low, &high);
 34:   for (i = 0; i < n; i++) {
 35:     iglobal = i + low;
 36:     value   = (PetscScalar)(i + 10 * rank);
 37:     VecSetValues(y, 1, &iglobal, &value, INSERT_VALUES);
 38:   }
 39:   VecAssemblyBegin(y);
 40:   VecAssemblyEnd(y);
 41:   VecView(y, PETSC_VIEWER_STDOUT_WORLD);

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

 48:   if (rank == 0) {
 49:     PetscPrintf(PETSC_COMM_SELF, "----\n");
 50:     VecView(x, PETSC_VIEWER_STDOUT_SELF);
 51:   }

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

 58:   PetscFinalize();
 59:   return 0;
 60: }

 62: /*TEST

 64:    test:
 65:       nsize: 2

 67: TEST*/