2: static char help[] = "Parallel vector layout.\n\n";

  4: /*
  5:   Include "petscvec.h" so that we can use vectors.  Note that this file
  6:   automatically includes:
  7:      petscsys.h       - base PETSc routines   petscis.h     - index sets
  8:      petscviewer.h - viewers
  9: */
 10: #include <petscvec.h>

 12: int main(int argc,char **argv)
 13: {
 14:   PetscMPIInt    rank;
 15:   PetscInt       i,istart,iend,n = 6,nlocal;
 16:   PetscScalar    v,*array;
 17:   Vec            x;
 18:   PetscViewer    viewer;

 20:   PetscInitialize(&argc,&argv,(char*)0,help);
 21:   MPI_Comm_rank(PETSC_COMM_WORLD,&rank);

 23:   PetscOptionsGetInt(NULL,NULL,"-n",&n,NULL);

 25:   /*
 26:      Create a vector, specifying only its global dimension.
 27:      When using VecCreate(), VecSetSizes() and VecSetFromOptions(),
 28:      the vector format (currently parallel or sequential) is
 29:      determined at runtime.  Also, the parallel partitioning of
 30:      the vector is determined by PETSc at runtime.
 31:   */
 32:   VecCreate(PETSC_COMM_WORLD,&x);
 33:   VecSetSizes(x,PETSC_DECIDE,n);
 34:   VecSetFromOptions(x);

 36:   /*
 37:      PETSc parallel vectors are partitioned by
 38:      contiguous chunks of rows across the processors.  Determine
 39:      which vector are locally owned.
 40:   */
 41:   VecGetOwnershipRange(x,&istart,&iend);

 43:   /* --------------------------------------------------------------------
 44:      Set the vector elements.
 45:       - Always specify global locations of vector entries.
 46:       - Each processor can insert into any location, even ones it does not own
 47:       - In this case each processor adds values to all the entries,
 48:          this is not practical, but is merely done as an example
 49:    */
 50:   for (i=0; i<n; i++) {
 51:     v    = (PetscReal)(rank*i);
 52:     VecSetValues(x,1,&i,&v,ADD_VALUES);
 53:   }

 55:   /*
 56:      Assemble vector, using the 2-step process:
 57:        VecAssemblyBegin(), VecAssemblyEnd()
 58:      Computations can be done while messages are in transition
 59:      by placing code between these two statements.
 60:   */
 61:   VecAssemblyBegin(x);
 62:   VecAssemblyEnd(x);

 64:   /*
 65:      Open an X-window viewer.  Note that we specify the same communicator
 66:      for the viewer as we used for the distributed vector (PETSC_COMM_WORLD).
 67:        - Helpful runtime option:
 68:             -draw_pause <pause> : sets time (in seconds) that the
 69:                   program pauses after PetscDrawPause() has been called
 70:                   (0 is default, -1 implies until user input).

 72:   */
 73:   PetscViewerDrawOpen(PETSC_COMM_WORLD,NULL,NULL,0,0,300,300,&viewer);
 74:   PetscObjectSetName((PetscObject)viewer,"Line graph Plot");
 75:   PetscViewerPushFormat(viewer,PETSC_VIEWER_DRAW_LG);
 76:   /*
 77:      View the vector
 78:   */
 79:   VecView(x,viewer);

 81:   /* --------------------------------------------------------------------
 82:        Access the vector values directly. Each processor has access only
 83:     to its portion of the vector. For default PETSc vectors VecGetArray()
 84:     does NOT involve a copy
 85:   */
 86:   VecGetLocalSize(x,&nlocal);
 87:   VecGetArray(x,&array);
 88:   for (i=0; i<nlocal; i++) array[i] = rank + 1;
 89:   VecRestoreArray(x,&array);

 91:   /*
 92:      View the vector
 93:   */
 94:   VecView(x,viewer);

 96:   /*
 97:      Free work space.  All PETSc objects should be destroyed when they
 98:      are no longer needed.
 99:   */
100:   PetscViewerPopFormat(viewer);
101:   PetscViewerDestroy(&viewer);
102:   VecDestroy(&x);

104:   PetscFinalize();
105:   return 0;
106: }

108: /*TEST

110:      test:
111:        nsize: 2

113: TEST*/