Actual source code: ex10.c
petsc-3.12.4 2020-02-04
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      2: static char help[]= "Scatters from a parallel vector to a sequential vector.\n\
      3: uses block index sets\n\n";

      5:  #include <petscvec.h>

      7: int main(int argc,char **argv)
      8: {
     10:   PetscInt       bs = 1,n = 5,ix0[3] = {5,7,9},ix1[3] = {2,3,4},i,iy0[3] = {1,2,4},iy1[3] = {0,1,3};
     11:   PetscMPIInt    size,rank;
     12:   PetscScalar    value;
     13:   Vec            x,y;
     14:   IS             isx,isy;
     15:   VecScatter     ctx = 0,newctx;

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

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

     23:   PetscOptionsGetInt(NULL,NULL,"-bs",&bs,NULL);
     24:   n    = bs*n;

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

     32:   /* create two index sets */
     33:   if (!rank) {
     34:     ISCreateBlock(PETSC_COMM_SELF,bs,3,ix0,PETSC_COPY_VALUES,&isx);
     35:     ISCreateBlock(PETSC_COMM_SELF,bs,3,iy0,PETSC_COPY_VALUES,&isy);
     36:   } else {
     37:     ISCreateBlock(PETSC_COMM_SELF,bs,3,ix1,PETSC_COPY_VALUES,&isx);
     38:     ISCreateBlock(PETSC_COMM_SELF,bs,3,iy1,PETSC_COPY_VALUES,&isy);
     39:   }

     41:   /* fill local part of parallel vector */
     42:   for (i=n*rank; i<n*(rank+1); i++) {
     43:     value = (PetscScalar) i;
     44:     VecSetValues(x,1,&i,&value,INSERT_VALUES);
     45:   }
     46:   VecAssemblyBegin(x);
     47:   VecAssemblyEnd(x);

     49:   VecView(x,PETSC_VIEWER_STDOUT_WORLD);

     51:   /* fill local part of parallel vector */
     52:   for (i=0; i<n; i++) {
     53:     value = -(PetscScalar) (i + 100*rank);
     54:     VecSetValues(y,1,&i,&value,INSERT_VALUES);
     55:   }
     56:   VecAssemblyBegin(y);
     57:   VecAssemblyEnd(y);

     60:   VecScatterCreate(x,isx,y,isy,&ctx);
     61:   VecScatterCopy(ctx,&newctx);
     62:   VecScatterDestroy(&ctx);

     64:   VecScatterBegin(newctx,y,x,INSERT_VALUES,SCATTER_REVERSE);
     65:   VecScatterEnd(newctx,y,x,INSERT_VALUES,SCATTER_REVERSE);
     66:   VecScatterDestroy(&newctx);

     68:   VecView(x,PETSC_VIEWER_STDOUT_WORLD);

     70:   ISDestroy(&isx);
     71:   ISDestroy(&isy);
     72:   VecDestroy(&x);
     73:   VecDestroy(&y);

     75:   PetscFinalize();
     76:   return ierr;
     77: }

     81: /*TEST

     83:    test:
     84:       nsize: 2

     86: TEST*/