Actual source code: ex2.c

  1: /*$Id: ex2.c,v 1.44 2001/09/07 20:09:05 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:   PetscScalar  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:   VecCreate(PETSC_COMM_WORLD,&x);
 37:   VecSetSizes(x,rank+1,PETSC_DECIDE);
 38:   VecSetFromOptions(x);
 39:   VecGetSize(x,&N);
 40:   VecSet(&one,x);

 42:   /*
 43:      Set the vector elements.
 44:       - Always specify global locations of vector entries.
 45:       - Each processor can contribute any vector entries,
 46:         regardless of which processor "owns" them; any nonlocal
 47:         contributions will be transferred to the appropriate processor
 48:         during the assembly process.
 49:       - In this example, the flag ADD_VALUES indicates that all
 50:         contributions will be added together.
 51:   */
 52:   for (i=0; i<N-rank; i++) {
 53:     VecSetValues(x,1,&i,&one,ADD_VALUES);
 54:   }

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

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

 71:   PetscFinalize();
 72:   return 0;
 73: }
 74: