Actual source code: ex2.c


  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>

 18: int main(int argc,char **argv)
 19: {
 20:   PetscMPIInt    rank;
 21:   PetscInt       i,N;
 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(x,one);

 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: }

 75: /*TEST

 77:      test:
 78:        nsize: 2

 80: TEST*/