Actual source code: ex42.c


  2: static char help[] = "Scatters from a parallel vector to a parallel vector.\n\n";

  4: #include <petscvec.h>

  6: int main(int argc, char **argv)
  7: {
  8:   PetscInt    n = 5, N, i;
  9:   PetscMPIInt size, rank;
 10:   PetscScalar value, zero = 0.0;
 11:   Vec         x, y;
 12:   IS          is1, is2;
 13:   VecScatter  ctx = 0;

 15:   PetscFunctionBeginUser;
 16:   PetscCall(PetscInitialize(&argc, &argv, (char *)0, 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, n, PETSC_DECIDE));
 24:   PetscCall(VecSetFromOptions(y));

 26:   PetscCall(VecCreate(PETSC_COMM_WORLD, &x));
 27:   PetscCall(VecSetSizes(x, n, PETSC_DECIDE));
 28:   PetscCall(VecSetFromOptions(x));

 30:   /* create two index sets */
 31:   PetscCall(ISCreateStride(PETSC_COMM_WORLD, n, n * rank, 1, &is1));
 32:   PetscCall(ISCreateStride(PETSC_COMM_WORLD, n, (n * (rank + 1)) % N, 1, &is2));

 34:   /* fill local part of parallel vector x */
 35:   value = (PetscScalar)(rank + 1);
 36:   for (i = n * rank; i < n * (rank + 1); i++) PetscCall(VecSetValues(x, 1, &i, &value, INSERT_VALUES));
 37:   PetscCall(VecAssemblyBegin(x));
 38:   PetscCall(VecAssemblyEnd(x));

 40:   PetscCall(VecSet(y, zero));

 42:   PetscCall(VecScatterCreate(x, is1, y, is2, &ctx));
 43:   for (i = 0; i < 100; i++) {
 44:     PetscReal ynorm;
 45:     PetscInt  j;
 46:     PetscCall(VecNormBegin(y, NORM_2, &ynorm));
 47:     PetscCall(PetscCommSplitReductionBegin(PetscObjectComm((PetscObject)y)));
 48:     for (j = 0; j < 3; j++) {
 49:       PetscCall(VecScatterBegin(ctx, x, y, ADD_VALUES, SCATTER_FORWARD));
 50:       PetscCall(VecScatterEnd(ctx, x, y, ADD_VALUES, SCATTER_FORWARD));
 51:     }
 52:     PetscCall(VecNormEnd(y, NORM_2, &ynorm));
 53:     /* PetscCall(PetscPrintf(PETSC_COMM_WORLD,"ynorm = %8.2G\n",ynorm)); */
 54:   }
 55:   PetscCall(VecScatterDestroy(&ctx));
 56:   PetscCall(VecView(y, PETSC_VIEWER_STDOUT_WORLD));

 58:   PetscCall(VecDestroy(&x));
 59:   PetscCall(VecDestroy(&y));
 60:   PetscCall(ISDestroy(&is1));
 61:   PetscCall(ISDestroy(&is2));

 63:   PetscCall(PetscFinalize());
 64:   return 0;
 65: }