Actual source code: ex4f90.F90

      1: !
      2: !     This introductory example illustrates running PETSc on a subset
      3: !     of processes
      4: !
      5: ! -----------------------------------------------------------------------
      6: #include <petsc/finclude/petscsys.h>
      7: program main
      8:   use petscsys
      9:   implicit none

     11:   PetscErrorCode ierr
     12:   PetscMPIInt rank, size
     13:   PetscMPIInt :: zero = 0, two = 2

     15: ! We must call MPI_Init() first, making us, not PETSc, responsible
     16: ! for MPI
     17:   PetscCallMPIA(MPI_Init(ierr))

     19: ! We can now change the communicator universe for PETSc
     20:   PetscCallMPIA(MPI_Comm_rank(MPI_COMM_WORLD, rank, ierr))
     21:   PetscCallMPIA(MPI_Comm_split(MPI_COMM_WORLD, mod(rank, two), zero, PETSC_COMM_WORLD, ierr))

     23: ! Every PETSc routine should begin with the PetscInitialize()
     24: ! routine.
     25:   PetscCallA(PetscInitialize(ierr))

     27: ! The following MPI calls return the number of processes being used
     28: ! and the rank of this process in the group.
     29:   PetscCallMPIA(MPI_Comm_size(PETSC_COMM_WORLD, size, ierr))
     30:   PetscCallMPIA(MPI_Comm_rank(PETSC_COMM_WORLD, rank, ierr))

     32: ! Here we would like to print only one message that represents all
     33: ! the processes in the group.
     34:   if (rank == 0) write (6, 100) size, rank
     35: 100 format('No of Procs = ', i4, ' rank = ', i4)

     37: ! Always call PetscFinalize() before exiting a program.  This
     38: ! routine - finalizes the PETSc libraries as well as MPI - provides
     39: ! summary and diagnostic information if certain runtime options are
     40: ! chosen (e.g., -log_view).  See PetscFinalize() manpage for more
     41: ! information.
     42:   PetscCallA(PetscFinalize(ierr))
     43:   PetscCallMPIA(MPI_Comm_free(PETSC_COMM_WORLD, ierr))

     45: ! Since we initialized MPI, we must call MPI_Finalize()
     46:   PetscCallMPIA(MPI_Finalize(ierr))
     47: end

     49: !
     50: !/*TEST
     51: !
     52: !   test:
     53: !
     54: !TEST*/