Actual source code: ex5.c

petsc-3.12.1 2019-10-22
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  2: static char help[] = "Scatters from a parallel vector to a sequential vector.\n\
  3: This does case when we are merely selecting the local part of the\n\
  4: parallel vector.\n\n";

  6:  #include <petscvec.h>

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

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

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

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

 32:   /* each processor inserts the entire vector */
 33:   /* this is redundant but tests assembly */
 34:   for (i=0; i<n*size; i++) {
 35:     value = (PetscScalar) i;
 36:     VecSetValues(x,1,&i,&value,INSERT_VALUES);
 37:   }
 38:   VecAssemblyBegin(x);
 39:   VecAssemblyEnd(x);
 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) {
 48:     PetscPrintf(PETSC_COMM_SELF,"----\n");
 49:     VecView(y,PETSC_VIEWER_STDOUT_SELF);
 50:   }

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

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

 61: /*TEST

 63:      test:
 64:        nsize: 2

 66: TEST*/