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

Actual source code: ex4f90.F90
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:       use petscsys
     14:       implicit none

     16:       integer ierr
     17:       integer rank, size

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

     22:       call MPI_Init(ierr)

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

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

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

     33:       call PetscInitialize(PETSC_NULL_CHARACTER,ierr)

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

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

     42: !     Here we would like to print only one message that represents all
     43: !     the processes in the group.
     44:       if (rank .eq. 0) write(6,100) size,rank
     45:  100  format("No of Procs = ",i4," rank = ",i4)

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

     53:       call PetscFinalize(ierr)

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

     57:       call  MPI_Finalize(ierr)
     58:       end