Actual source code: ex11.c


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

  4: #include <petscvec.h>

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

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

 20:   /* create two vectors */
 21:   VecCreate(PETSC_COMM_WORLD, &x);
 22:   VecSetSizes(x, rank + 1, PETSC_DECIDE);
 23:   VecSetFromOptions(x);
 24:   VecGetSize(x, &N);
 25:   VecCreateSeq(PETSC_COMM_SELF, N - rank, &y);

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

 31:   /* fill parallel vector: note this is not efficient way*/
 32:   for (i = 0; i < N; i++) {
 33:     value = (PetscScalar)i;
 34:     VecSetValues(x, 1, &i, &value, INSERT_VALUES);
 35:   }
 36:   VecAssemblyBegin(x);
 37:   VecAssemblyEnd(x);
 38:   VecSet(y, -1.0);

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

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

 61: /*TEST

 63:    test:
 64:       nsize: 2

 66:    test:
 67:       suffix: bts
 68:       nsize: 2
 69:       args: -vec_assembly_legacy
 70:       output_file: output/ex11_1.out

 72: TEST*/