Actual source code: ex17.c

petsc-3.12.0 2019-09-29
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  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: {
 10:   PetscInt       n = 5,N,low,high,iglobal,i;
 11:   PetscMPIInt    size,rank;
 12:   PetscScalar    value,zero = 0.0;
 13:   Vec            x,y;
 14:   IS             is1,is2;
 15:   VecScatter     ctx;

 17:   PetscInitialize(&argc,&argv,(char*)0,help);if (ierr) return ierr;
 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; value = (PetscScalar) (i + 10*rank);
 36:     VecSetValues(y,1,&iglobal,&value,INSERT_VALUES);
 37:   }
 38:   VecAssemblyBegin(y);
 39:   VecAssemblyEnd(y);
 40:   VecView(y,PETSC_VIEWER_STDOUT_WORLD);

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

 47:   if (!rank) {
 48:     printf("----\n");
 49:     VecView(x,PETSC_VIEWER_STDOUT_SELF);
 50:   }

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

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



 63: /*TEST

 65:    test:
 66:       nsize: 2

 68: TEST*/