Actual source code: ex23.c

  2: static char help[] = "Scatters from a parallel vector to a sequential vector.\n\
  3:   Using a blocked send and a strided receive.\n\n";

  5: /*
  6:         0 1 2 3 | 4 5 6 7 ||  8 9 10 11 

  8:      Scatter first and third block to first processor and 
  9:      second and third block to second processor
 10: */
 11:  #include petscvec.h

 15: int main(int argc,char **argv)
 16: {
 18:   PetscInt       i,blocks[2],nlocal;
 19:   PetscMPIInt    size,rank;
 20:   PetscScalar    value;
 21:   Vec            x,y;
 22:   IS             is1,is2;
 23:   VecScatter     ctx = 0;

 25:   PetscInitialize(&argc,&argv,(char*)0,help);
 26:   MPI_Comm_size(PETSC_COMM_WORLD,&size);
 27:   MPI_Comm_rank(PETSC_COMM_WORLD,&rank);

 29:   if (size != 2) SETERRQ(1,"Must run with 2 processors");

 31:   /* create two vectors */
 32:   if (!rank) nlocal = 8;
 33:   else nlocal = 4;
 34:   VecCreate(PETSC_COMM_WORLD,&x);
 35:   VecSetSizes(x,nlocal,12);
 36:   VecSetFromOptions(x);
 37:   VecCreateSeq(PETSC_COMM_SELF,8,&y);

 39:   /* create two index sets */
 40:   if (!rank) {
 41:     blocks[0] = 0; blocks[1] = 8;
 42:   } else {
 43:     blocks[0] = 4; blocks[1] = 8;
 44:   }
 45:   ISCreateBlock(PETSC_COMM_SELF,4,2,blocks,&is1);
 46:   ISCreateStride(PETSC_COMM_SELF,8,0,1,&is2);

 48:   for (i=0; i<12; i++) {
 49:     value = i;
 50:     VecSetValues(x,1,&i,&value,INSERT_VALUES);
 51:   }
 52:   VecAssemblyBegin(x);
 53:   VecAssemblyEnd(x);

 55:   VecScatterCreate(x,is1,y,is2,&ctx);
 56:   VecScatterBegin(ctx,x,y,INSERT_VALUES,SCATTER_FORWARD);
 57:   VecScatterEnd(ctx,x,y,INSERT_VALUES,SCATTER_FORWARD);
 58:   VecScatterDestroy(ctx);
 59: 
 60:   PetscSleep(2.0*rank);
 61:   VecView(y,PETSC_VIEWER_STDOUT_SELF);

 63:   VecDestroy(x);
 64:   VecDestroy(y);
 65:   ISDestroy(is1);
 66:   ISDestroy(is2);

 68:   PetscFinalize();
 69:   return 0;
 70: }
 71: