Actual source code: ex4f90.F90
petsc-3.13.6 2020-09-29
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      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:  #include <petsc/finclude/petscsys.h>
     14:       use petscsys
     15:       implicit none

     17:       PetscErrorCode ierr
     18:       PetscMPIInt rank, size, two

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

     23:       call MPI_Init(ierr)
     24:       if (ierr .ne. 0) then
     25:          print*,'Unable to initialize MPI'
     26:          stop
     27:       endif

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

     31:       two = 2
     32:       call MPI_Comm_rank(MPI_COMM_WORLD,rank,ierr)
     33:       call MPI_Comm_split(MPI_COMM_WORLD,mod(rank,two),0,PETSC_COMM_WORLD,ierr)

     35: !     Every PETSc routine should begin with the PetscInitialize()
     36: !     routine.

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

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

     47:       call MPI_Comm_size(PETSC_COMM_WORLD,size,ierr);CHKERRA(ierr)
     48:       call MPI_Comm_rank(PETSC_COMM_WORLD,rank,ierr);CHKERRA(ierr)

     51: !     Here we would like to print only one message that represents all
     52: !     the processes in the group.
     53:       if (rank .eq. 0) write(6,100) size,rank
     54:  100  format('No of Procs = ',i4,' rank = ',i4)

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

     62:       call PetscFinalize(ierr)
     63:       call MPI_Comm_free(PETSC_COMM_WORLD,ierr)

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

     67:       call  MPI_Finalize(ierr)
     68:       end

     70: !
     71: !/*TEST
     72: !
     73: !   test:
     74: !
     75: !TEST*/