Actual source code: ex4f90.F90

  1: !
  2: !     This introductory example illustrates running PETSc on a subset
  3: !     of processes
  4: !
  5: ! -----------------------------------------------------------------------

  7:       program main
  8: #include <petsc/finclude/petscsys.h>
  9:       use petscmpi  ! or mpi or mpi_f08
 10:       use petscsys
 11:       implicit none

 13:       PetscErrorCode ierr
 14:       PetscMPIInt rank, size, zero, two

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

 19:       call MPI_Init(ierr)
 20:       if (ierr .ne. 0) then
 21:          print*,'Unable to initialize MPI'
 22:          stop
 23:       endif

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

 27:       zero = 0
 28:       two = 2
 29:       call MPI_Comm_rank(MPI_COMM_WORLD,rank,ierr)
 30:       call MPI_Comm_split(MPI_COMM_WORLD,mod(rank,two),zero,PETSC_COMM_WORLD,ierr)

 32: !     Every PETSc routine should begin with the PetscInitialize()
 33: !     routine.

 35:       call PetscInitialize(PETSC_NULL_CHARACTER,ierr)
 36:       if (ierr .ne. 0) then
 37:         print*,'Unable to initialize PETSc'
 38:         stop
 39:       endif

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

 44:       call MPI_Comm_size(PETSC_COMM_WORLD,size,ierr);CHKERRA(ierr)
 45:       call MPI_Comm_rank(PETSC_COMM_WORLD,rank,ierr);CHKERRA(ierr)

 47: !     Here we would like to print only one message that represents all
 48: !     the processes in the group.
 49:       if (rank .eq. 0) write(6,100) size,rank
 50:  100  format('No of Procs = ',i4,' rank = ',i4)

 52: !     Always call PetscFinalize() before exiting a program.  This
 53: !     routine - finalizes the PETSc libraries as well as MPI - provides
 54: !     summary and diagnostic information if certain runtime options are
 55: !     chosen (e.g., -log_view).  See PetscFinalize() manpage for more
 56: !     information.

 58:       call PetscFinalize(ierr)
 59:       call MPI_Comm_free(PETSC_COMM_WORLD,ierr)

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

 63:       call  MPI_Finalize(ierr)
 64:       end

 66: !
 67: !/*TEST
 68: !
 69: !   test:
 70: !
 71: !TEST*/