Actual source code: ex11.c

petsc-3.13.4 2020-08-01
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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:   PetscMPIInt    size,rank;
 10:   PetscInt       i,N;
 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,rank+1,PETSC_DECIDE);
 23:   VecSetFromOptions(x);
 24:   VecGetSize(x,&N);
 25:   VecCreateSeq(PETSC_COMM_SELF,N-rank,&y);

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

 31:   /* fill parallel vector: note this is not efficient way*/
 32:   for (i=0; i<N; i++) {
 33:     value = (PetscScalar) i;
 34:     VecSetValues(x,1,&i,&value,INSERT_VALUES);
 35:   }
 36:   VecAssemblyBegin(x);
 37:   VecAssemblyEnd(x);
 38:   VecSet(y,-1.0);

 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:     printf("----\n");
 49:     VecView(y,PETSC_VIEWER_STDOUT_SELF);
 50:   }

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

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



 63: /*TEST

 65:    test:
 66:       nsize: 2

 68:    test:
 69:       suffix: bts
 70:       nsize: 2
 71:       args: -vec_assembly_legacy
 72:       output_file: output/ex11_1.out

 74: TEST*/