Date: 2022-03-31T04:46:30+00:00

Actual source code: ex2f.F

      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: !/*T
      8: !   Concepts: vectors^assembling
      9: !   Processors: n
     10: !T*/
     11: ! -----------------------------------------------------------------------

     13:       program main
     14: #include <petsc/finclude/petscvec.h>
     15:       use petscvec
     16:       implicit none

     18: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     19: !                 Beginning of program
     20: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

     22:       Vec     x
     23:       PetscInt N,i,ione
     24:       PetscErrorCode ierr
     25:       PetscMPIInt rank
     26:       PetscScalar  one

     28:       call PetscInitialize(PETSC_NULL_CHARACTER,ierr)
     29:       if (ierr .ne. 0) then
     30:         print*,'PetscInitialize failed'
     31:         stop
     32:       endif
     33:       one   = 1.0
     34:       call MPI_Comm_rank(PETSC_COMM_WORLD,rank,ierr)

     36: !  Create a parallel vector.
     37: !   - In this case, we specify the size of the local portion on
     38: !     each processor, and PETSc computes the global size.  Alternatively,
     39: !     if we pass the global size and use PETSC_DECIDE for the
     40: !     local size PETSc will choose a reasonable partition trying
     41: !     to put nearly an equal number of elements on each processor.

     43:       N = rank + 1
     44:       call VecCreateMPI(PETSC_COMM_WORLD,N,PETSC_DECIDE,x,ierr)
     45:       call VecGetSize(x,N,ierr)
     46:       call VecSet(x,one,ierr)

     48: !  Set the vector elements.
     49: !   - Note that VecSetValues() uses 0-based row and column numbers
     50: !     in Fortran as well as in C.
     51: !   - Always specify global locations of vector entries.
     52: !   - Each processor can contribute any vector entries,
     53: !     regardless of which processor "owns" them; any nonlocal
     54: !     contributions will be transferred to the appropriate processor
     55: !     during the assembly process.
     56: !   - In this example, the flag ADD_VALUES indicates that all
     57: !     contributions will be added together.

     59:       ione = 1
     60:       do 100 i=0,N-rank-1
     61:          call VecSetValues(x,ione,i,one,ADD_VALUES,ierr)
     62:  100  continue

     64: !  Assemble vector, using the 2-step process:
     65: !    VecAssemblyBegin(), VecAssemblyEnd()
     66: !  Computations can be done while messages are in transition
     67: !  by placing code between these two statements.

     69:       call VecAssemblyBegin(x,ierr)
     70:       call VecAssemblyEnd(x,ierr)

     72: !     Test VecGetValues() with scalar entries
     73:       if (rank .eq. 0) then
     74:         ione = 0
     75:         call VecGetValues(x,ione,i,one,ierr)
     76:       endif

     78: !  View the vector; then destroy it.

     80:       call VecView(x,PETSC_VIEWER_STDOUT_WORLD,ierr)
     81:       call VecDestroy(x,ierr)

     83:       call PetscFinalize(ierr)
     84:       end

     86: !/*TEST
     87: !
     88: !     test:
     89: !       nsize: 2
     90: !       filter: grep -v "MPI processes"
     91: !
     92: !TEST*/