Actual source code: ex1.c

petsc-master 2017-06-24
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  2: static char help[] = "Creating a general index set.\n\n";

  4: /*T
  5:     Concepts: index sets^manipulating a general index set;
  6:     Concepts: index sets^creating general;
  7:     Concepts: IS^creating a general index set;

  9:     Description: Creates an index set based on a set of integers. Views that index set
 10:     and then destroys it.

 12: T*/

 14: /*
 15:     Include petscis.h so we can use PETSc IS objects. Note that this automatically
 16:   includes petscsys.h.
 17: */
 18:  #include <petscis.h>
 19:  #include <petscviewer.h>

 21: int main(int argc,char **argv)
 22: {
 24:   PetscInt       *indices,n;
 25:   const PetscInt *nindices;
 26:   PetscMPIInt    rank;
 27:   IS             is;

 29:   PetscInitialize(&argc,&argv,(char*)0,help);if (ierr) return ierr;
 30:   MPI_Comm_rank(PETSC_COMM_WORLD,&rank);

 32:   /*
 33:      Create an index set with 5 entries. Each processor creates
 34:    its own index set with its own list of integers.
 35:   */
 36:   PetscMalloc1(5,&indices);
 37:   indices[0] = rank + 1;
 38:   indices[1] = rank + 2;
 39:   indices[2] = rank + 3;
 40:   indices[3] = rank + 4;
 41:   indices[4] = rank + 5;
 42:   ISCreateGeneral(PETSC_COMM_SELF,5,indices,PETSC_COPY_VALUES,&is);
 43:   /*
 44:      Note that ISCreateGeneral() has made a copy of the indices
 45:      so we may (and generally should) free indices[]
 46:   */
 47:   PetscFree(indices);

 49:   /*
 50:      Print the index set to stdout
 51:   */
 52:   ISView(is,PETSC_VIEWER_STDOUT_SELF);

 54:   /*
 55:      Get the number of indices in the set
 56:   */
 57:   ISGetLocalSize(is,&n);

 59:   /*
 60:      Get the indices in the index set
 61:   */
 62:   ISGetIndices(is,&nindices);
 63:   /*
 64:      Now any code that needs access to the list of integers
 65:    has access to it here through indices[].
 66:    */
 67:   PetscPrintf(PETSC_COMM_SELF,"[%d] First index %D\n",rank,nindices[0]);

 69:   /*
 70:      Once we no longer need access to the indices they should
 71:      returned to the system
 72:   */
 73:   ISRestoreIndices(is,&nindices);

 75:   /*
 76:      One should destroy any PETSc object once one is completely
 77:     done with it.
 78:   */
 79:   ISDestroy(&is);
 80:   PetscFinalize();
 81:   return ierr;
 82: }