Actual source code: ex42.c

petsc-3.7.3 2016-07-24
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  2: static char help[] = "Scatters from a parallel vector to a parallel vector.\n\n";

  4: #include <petscvec.h>

  8: int main(int argc,char **argv)
  9: {
 11:   PetscInt       n = 5,N,i;
 12:   PetscMPIInt    size,rank;
 13:   PetscScalar    value,zero = 0.0;
 14:   Vec            x,y;
 15:   IS             is1,is2;
 16:   VecScatter     ctx = 0;

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

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

 28:   VecCreate(PETSC_COMM_WORLD,&x);
 29:   VecSetSizes(x,n,PETSC_DECIDE);
 30:   VecSetFromOptions(x);

 32:   /* create two index sets */
 33:   ISCreateStride(PETSC_COMM_WORLD,n,n*rank,1,&is1);
 34:   ISCreateStride(PETSC_COMM_WORLD,n,(n*(rank+1))%N,1,&is2);

 36:   /* fill local part of parallel vector x */
 37:   value = (PetscScalar)(rank+1);
 38:   for (i=n*rank; i<n*(rank+1); i++) {
 39:     VecSetValues(x,1,&i,&value,INSERT_VALUES);
 40:   }
 41:   VecAssemblyBegin(x);
 42:   VecAssemblyEnd(x);

 44:   VecSet(y,zero);

 46:   VecScatterCreate(x,is1,y,is2,&ctx);
 47:   for (i=0; i<100; i++) {
 48:     PetscReal ynorm;
 49:     PetscInt  j;
 50:     VecNormBegin(y,NORM_2,&ynorm);
 51:     PetscCommSplitReductionBegin(PetscObjectComm((PetscObject)y));
 52:     for (j=0; j<3; j++) {
 53:       VecScatterBegin(ctx,x,y,ADD_VALUES,SCATTER_FORWARD);
 54:       VecScatterEnd(ctx,x,y,ADD_VALUES,SCATTER_FORWARD);
 55:     }
 56:     VecNormEnd(y,NORM_2,&ynorm);
 57:     /* PetscPrintf(PETSC_COMM_WORLD,"ynorm = %8.2G\n",ynorm); */
 58:   }
 59:   VecScatterDestroy(&ctx);
 60:   VecView(y,PETSC_VIEWER_STDOUT_WORLD);

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

 67:   PetscFinalize();
 68:   return 0;
 69: }