1: !
  2: !
  3: !  Description: Builds a parallel vector with 1 component on the first
  4: !               processor, 2 on the second, etc.  Then each processor adds
  5: !               one to all elements except the last rank.
  6: !
  7: ! -----------------------------------------------------------------------

  9:       program main
 10: #include <petsc/finclude/petscvec.h>
 11:       use petscvec
 12:       implicit none

 14: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 15: !                 Beginning of program
 16: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

 18:       Vec     x
 19:       PetscInt N,i,ione
 20:       PetscErrorCode ierr
 21:       PetscMPIInt rank
 22:       PetscScalar  one

 24:       call PetscInitialize(PETSC_NULL_CHARACTER,ierr)
 25:       if (ierr .ne. 0) then
 26:         print*,'PetscInitialize failed'
 27:         stop
 28:       endif
 29:       one   = 1.0
 30:       call MPI_Comm_rank(PETSC_COMM_WORLD,rank,ierr)

 32: !  Create a parallel vector.
 33: !   - In this case, we specify the size of the local portion on
 34: !     each processor, 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.

 39:       N = rank + 1
 40:       call VecCreateMPI(PETSC_COMM_WORLD,N,PETSC_DECIDE,x,ierr)
 41:       call VecGetSize(x,N,ierr)
 42:       call VecSet(x,one,ierr)

 44: !  Set the vector elements.
 45: !   - Note that VecSetValues() uses 0-based row and column numbers
 46: !     in Fortran as well as in C.
 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.

 55:       ione = 1
 56:       do 100 i=0,N-rank-1
 57:          call VecSetValues(x,ione,i,one,ADD_VALUES,ierr)
 58:  100  continue

 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.

 65:       call VecAssemblyBegin(x,ierr)
 66:       call VecAssemblyEnd(x,ierr)

 68: !     Test VecGetValues() with scalar entries
 69:       if (rank .eq. 0) then
 70:         ione = 0
 71:         call VecGetValues(x,ione,i,one,ierr)
 72:       endif

 74: !  View the vector; then destroy it.

 76:       call VecView(x,PETSC_VIEWER_STDOUT_WORLD,ierr)
 77:       call VecDestroy(x,ierr)

 79:       call PetscFinalize(ierr)
 80:       end

 82: !/*TEST
 83: !
 84: !     test:
 85: !       nsize: 2
 86: !       filter: grep -v "MPI processes"
 87: !
 88: !TEST*/