Actual source code: ex9.c

petsc-3.12.2 2019-11-22
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  2: static char help[]= "Scatters from a parallel vector to a sequential vector.\n\n";

  4:  #include <petscvec.h>

  6: int main(int argc,char **argv)
  7: {
  9:   PetscInt       n = 5,i,idx2[3] = {0,2,3},idx1[3] = {0,1,2};
 10:   PetscMPIInt    size,rank;
 11:   PetscScalar    value;
 12:   Vec            x,y;
 13:   IS             is1,is2;
 14:   VecScatter     ctx = 0;

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

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

 26:   /* create two index sets */
 27:   ISCreateGeneral(PETSC_COMM_SELF,3,idx1,PETSC_COPY_VALUES,&is1);
 28:   ISCreateGeneral(PETSC_COMM_SELF,3,idx2,PETSC_COPY_VALUES,&is2);

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

 38:   VecView(x,PETSC_VIEWER_STDOUT_WORLD);

 40:   VecSet(y,-1.0);

 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,"scattered vector\n");
 49:     VecView(y,PETSC_VIEWER_STDOUT_SELF);
 50:   }
 51:   ISDestroy(&is1);
 52:   ISDestroy(&is2);
 53:   VecDestroy(&x);
 54:   VecDestroy(&y);

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



 62: /*TEST

 64:    test:
 65:       nsize: 2

 67: TEST*/