Actual source code: ex4f.F

petsc-3.13.0 2020-03-29
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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
 16:       PetscErrorCode ierr
 17:       PetscMPIInt    rank, size,grank,two
 18:       PetscReal globalrank

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

 23:       call MPI_Init(ierr)

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

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

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

 35:       call PetscInitializeNoArguments(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)
 45:       call MPI_Comm_rank(PETSC_COMM_WORLD,rank,ierr)


 48: !     Here we would like to print only one message that represents all
 49: !     the processes in the group. Sleep so that IO from different ranks
 50: !     don't get mixed up. Note this is not an ideal solution
 51:       call MPI_Comm_rank(MPI_COMM_WORLD,grank,ierr)
 52:       globalrank = grank
 53:       call PetscSleep(globalrank,ierr)
 54:       if (rank .eq. 0) write(6,100) size,rank
 55:  100  format('No of Procs = ',i4,' rank = ',i4)

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

 63:       call PetscFinalize(ierr)

 65:       call MPI_Comm_free(PETSC_COMM_WORLD,ierr)


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

 70:       call  MPI_Finalize(ierr)
 71:       end

 73: !/*TEST
 74: !
 75: !   test:
 76: !      nsize: 5
 77: !      filter: sort -b
 78: !      filter_output: sort -b
 79: !      requires: !cuda
 80: !
 81: !TEST*/