1: /*$Id: ex3.c,v 1.56 2001/08/07 21:29:27 bsmith Exp $*/

  3: static char help[] = "Parallel vector layout.nn";

  5: /*T
  6:    Concepts: vectors^setting values
  7:    Concepts: vectors^local access to
  8:    Concepts: vectors^drawing vectors;
  9:    Processors: n
 10: T*/

 12: /* 
 13:   Include "petscvec.h" so that we can use vectors.  Note that this file
 14:   automatically includes:
 15:      petsc.h       - base PETSc routines   petscis.h     - index sets
 16:      petscsys.h    - system routines       petscviewer.h - viewers
 17: */
 18:  #include petscvec.h

 20: #undef __FUNCT__
 22: int main(int argc,char **argv)
 23: {
 24:   int         i,istart,iend,n = 6,ierr,rank,nlocal;
 25:   PetscScalar v,*array;
 26:   Vec         x;
 27:   PetscViewer viewer;

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

 32:   PetscOptionsGetInt(PETSC_NULL,"-n",&n,PETSC_NULL);
 33: 
 34:   /* 
 35:      Create a vector, specifying only its global dimension.
 36:      When using VecCreate(), VecSetSizes() and VecSetFromOptions(), 
 37:      the vector format (currently parallel or sequential) is 
 38:      determined at runtime.  Also, the parallel partitioning of 
 39:      the vector is determined by PETSc at runtime.
 40:   */
 41:   VecCreate(PETSC_COMM_WORLD,&x);
 42:   VecSetSizes(x,PETSC_DECIDE,n);
 43:   VecSetFromOptions(x);

 45:   /* 
 46:      PETSc parallel vectors are partitioned by
 47:      contiguous chunks of rows across the processors.  Determine
 48:      which vector are locally owned. 
 49:   */
 50:   VecGetOwnershipRange(x,&istart,&iend);

 52:   /* -------------------------------------------------------------------- 
 53:      Set the vector elements.
 54:       - Always specify global locations of vector entries.
 55:       - Each processor can insert into any location, even ones it does not own
 56:       - In this case each processor adds values to all the entries,
 57:          this is not practical, but is merely done as an example
 58:    */
 59:   for (i=0; i<n; i++) {
 60:     v = (PetscReal)(rank*i);
 61:     VecSetValues(x,1,&i,&v,ADD_VALUES);
 62:   }

 64:   /* 
 65:      Assemble vector, using the 2-step process:
 66:        VecAssemblyBegin(), VecAssemblyEnd()
 67:      Computations can be done while messages are in transition
 68:      by placing code between these two statements.
 69:   */
 70:   VecAssemblyBegin(x);
 71:   VecAssemblyEnd(x);

 73:   /*
 74:      Open an X-window viewer.  Note that we specify the same communicator
 75:      for the viewer as we used for the distributed vector (PETSC_COMM_WORLD).
 76:        - Helpful runtime option:
 77:             -draw_pause <pause> : sets time (in seconds) that the
 78:                   program pauses after PetscDrawPause() has been called
 79:                   (0 is default, -1 implies until user input).

 81:   */
 82:   PetscViewerDrawOpen(PETSC_COMM_WORLD,PETSC_NULL,PETSC_NULL,0,0,300,300,&viewer);
 83:   PetscObjectSetName((PetscObject)viewer,"Line graph Plot");
 84:   PetscViewerPushFormat(viewer,PETSC_VIEWER_DRAW_LG);
 85:   /*
 86:      View the vector
 87:   */
 88:   VecView(x,viewer);

 90:   /* --------------------------------------------------------------------
 91:        Access the vector values directly. Each processor has access only 
 92:     to its portion of the vector. For default PETSc vectors VecGetArray()
 93:     does NOT involve a copy
 94:   */
 95:   VecGetLocalSize(x,&nlocal);
 96:   VecGetArray(x,&array);
 97:   for (i=0; i<nlocal; i++) {
 98:     array[i] = rank + 1;
 99:   }
100:   VecRestoreArray(x,&array);

102:   /*
103:      View the vector
104:   */
105:   VecView(x,viewer);

107:   /* 
108:      Free work space.  All PETSc objects should be destroyed when they
109:      are no longer needed.
110:   */
111:   PetscViewerDestroy(viewer);
112:   VecDestroy(x);

114:   PetscFinalize();
115:   return 0;
116: }
117: