Actual source code: ex2.c
petsc-3.4.2 2013-07-02

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

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

     10: /*
     11:   Include "petscvec.h" so that we can use vectors.  Note that this file
     12:   automatically includes:
     13:      petscsys.h       - base PETSc routines   petscis.h     - index sets
     14:      petscviewer.h - viewers
     15: */
     16: #include <petscvec.h>

     20: int main(int argc,char **argv)
     21: {
     23:   PetscMPIInt    rank;
     24:   PetscInt       i,N;
     25:   PetscScalar    one = 1.0;
     26:   Vec            x;

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

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

     45:   /*
     46:      Set the vector elements.
     47:       - Always specify global locations of vector entries.
     48:       - Each processor can contribute any vector entries,
     49:         regardless of which processor "owns" them; any nonlocal
     50:         contributions will be transferred to the appropriate processor
     51:         during the assembly process.
     52:       - In this example, the flag ADD_VALUES indicates that all
     53:         contributions will be added together.
     54:   */
     55:   for (i=0; i<N-rank; i++) {
     56:     VecSetValues(x,1,&i,&one,ADD_VALUES);
     57:   }

     59:   /*
     60:      Assemble vector, using the 2-step process:
     61:        VecAssemblyBegin(), VecAssemblyEnd()
     62:      Computations can be done while messages are in transition
     63:      by placing code between these two statements.
     64:   */
     65:   VecAssemblyBegin(x);
     66:   VecAssemblyEnd(x);

     68:   /*
     69:       View the vector; then destroy it.
     70:   */
     71:   VecView(x,PETSC_VIEWER_STDOUT_WORLD);
     72:   VecDestroy(&x);

     74:   PetscFinalize();
     75:   return 0;
     76: }