Actual source code: ex9.c

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

 4:  #include petscvec.h
 5:  #include petscsys.h

  9: int main(int argc,char **argv)
 10: {
 12:   PetscInt       n = 5,i,idx2[3] = {0,2,3},idx1[3] = {0,1,2};
 13:   PetscMPIInt    size,rank;
 14:   PetscScalar    value;
 15:   Vec            x,y;
 16:   IS             is1,is2;
 17:   VecScatter     ctx = 0;

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

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

 29:   /* create two index sets */
 30:   ISCreateGeneral(PETSC_COMM_SELF,3,idx1,&is1);
 31:   ISCreateGeneral(PETSC_COMM_SELF,3,idx2,&is2);

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

 41:   VecView(x,PETSC_VIEWER_STDOUT_WORLD);

 43:   VecSet(y,-1.0);

 45:   VecScatterCreate(x,is1,y,is2,&ctx);
 46:   VecScatterBegin(ctx,x,y,INSERT_VALUES,SCATTER_FORWARD);
 47:   VecScatterEnd(ctx,x,y,INSERT_VALUES,SCATTER_FORWARD);
 48:   VecScatterDestroy(ctx);

 50:   if (!rank) {
 51:     PetscPrintf(PETSC_COMM_SELF,"scattered vector\n");
 52:     VecView(y,PETSC_VIEWER_STDOUT_SELF);
 53:   }
 54:   ISDestroy(is1);
 55:   ISDestroy(is2);
 56:   VecDestroy(x);
 57:   VecDestroy(y);

 59:   PetscFinalize();
 60:   return 0;
 61: }
 62: