Date: 2013-07-02T14:39:26+00:00

Actual source code: ex4f.F
petsc-3.4.2 2013-07-02

      1: !
      2: !     This introductory example illustrates running PETSc on a subset
      3: !     of processes
      4: !
      5: !/*T
      6: !   Concepts: introduction to PETSc;
      7: !   Concepts: process^subset set PETSC_COMM_WORLD
      8: !   Processors: 2
      9: !T*/
     10: ! -----------------------------------------------------------------------

     12:       program main
     13:       implicit none
     14: #include <finclude/petscsys.h>
     15:       PetscErrorCode ierr
     16:       PetscMPIInt    rank, size

     18: !     We must call MPI_Init() first, making us, not PETSc, responsible
     19: !     for MPI

     21:       call MPI_Init(ierr)

     23: !     We can now change the communicator universe for PETSc

     25:       call MPI_Comm_rank(MPI_COMM_WORLD,rank,ierr)
     26:       call MPI_Comm_split(MPI_COMM_WORLD,mod(rank,2),0,                 &
     27:      &     PETSC_COMM_WORLD,ierr)

     29: !     Every PETSc routine should begin with the PetscInitialize()
     30: !     routine.

     32:       call PetscInitialize(PETSC_NULL_CHARACTER,ierr)

     34: !     The following MPI calls return the number of processes being used
     35: !     and the rank of this process in the group.

     37:       call MPI_Comm_size(PETSC_COMM_WORLD,size,ierr)
     38:       call MPI_Comm_rank(PETSC_COMM_WORLD,rank,ierr)

     41: !     Here we would like to print only one message that represents all
     42: !     the processes in the group.
     43:       if (rank .eq. 0) write(6,100) size,rank
     44:  100  format("No of Procs = ",i4," rank = ",i4)

     46: !     Always call PetscFinalize() before exiting a program.  This
     47: !     routine - finalizes the PETSc libraries as well as MPI - provides
     48: !     summary and diagnostic information if certain runtime options are
     49: !     chosen (e.g., -log_summary).  See PetscFinalize() manpage for more
     50: !     information.

     52:       call PetscFinalize(ierr)

     54: !     Since we initialized MPI, we must call MPI_Finalize()

     56:       call  MPI_Finalize(ierr)
     57:       end