Actual source code: ex2.c

  1: /*$Id: ex2.c,v 1.42 2001/04/10 19:35:06 bsmith Exp $*/

  3: static char help[] = "Builds a parallel vector with 1 component on the firstprocessor, 2 on the second, etc.n
  4:   Then each processor adds one to all elements except the last rank.nn";

  6: /*T
  7:    Concepts: vectors^assembling vectors;
  8:    Processors: n
  9: T*/

 11: /* 
 12:   Include "petscvec.h" so that we can use vectors.  Note that this file
 13:   automatically includes:
 14:      petsc.h       - base PETSc routines   petscis.h     - index sets
 15:      petscsys.h    - system routines       petscviewer.h - viewers
 16: */
 17: #include "petscvec.h"

 19: int main(int argc,char **argv)
 20: {
 21:   int     i,N,ierr,rank;
 22:   Scalar  one = 1.0;
 23:   Vec     x;

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

 28:   /*
 29:      Create a parallel vector.
 30:       - In this case, we specify the size of each processor's local
 31:         portion, and PETSc computes the global size.  Alternatively,
 32:         if we pass the global size and use PETSC_DECIDE for the 
 33:         local size PETSc will choose a reasonable partition trying 
 34:         to put nearly an equal number of elements on each processor.
 35:   */
 36:   VecCreateMPI(PETSC_COMM_WORLD,rank+1,PETSC_DECIDE,&x);
 37:   VecGetSize(x,&N);
 38:   VecSet(&one,x);

 40:   /*
 41:      Set the vector elements.
 42:       - Always specify global locations of vector entries.
 43:       - Each processor can contribute any vector entries,
 44:         regardless of which processor "owns" them; any nonlocal
 45:         contributions will be transferred to the appropriate processor
 46:         during the assembly process.
 47:       - In this example, the flag ADD_VALUES indicates that all
 48:         contributions will be added together.
 49:   */
 50:   for (i=0; i<N-rank; i++) {
 51:     VecSetValues(x,1,&i,&one,ADD_VALUES);
 52:   }

 54:   /* 
 55:      Assemble vector, using the 2-step process:
 56:        VecAssemblyBegin(), VecAssemblyEnd()
 57:      Computations can be done while messages are in transition
 58:      by placing code between these two statements.
 59:   */
 60:   VecAssemblyBegin(x);
 61:   VecAssemblyEnd(x);

 63:   /*
 64:       View the vector; then destroy it.
 65:   */
 66:   VecView(x,PETSC_VIEWER_STDOUT_WORLD);
 67:   VecDestroy(x);

 69:   PetscFinalize();
 70:   return 0;
 71: }
 72: