Actual source code: ex4f.F
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
12: PetscErrorCode ierr
13: PetscMPIInt rank, size,grank,zero,two
14: PetscReal globalrank
16: ! We must call MPI_Init() first, making us, not PETSc, responsible
17: ! for MPI
19: call MPI_Init(ierr)
20: #if defined(PETSC_HAVE_ELEMENTAL)
21: call PetscElementalInitializePackage(ierr)
22: #endif
23: ! We can now change the communicator universe for PETSc
25: zero = 0
26: two = 2
27: call MPI_Comm_rank(MPI_COMM_WORLD,rank,ierr)
28: call MPI_Comm_split(MPI_COMM_WORLD,mod(rank,two),zero, &
29: & PETSC_COMM_WORLD,ierr)
31: ! Every PETSc routine should begin with the PetscInitialize()
32: ! routine.
33: call PetscInitializeNoArguments(ierr)
34: if (ierr .ne. 0) then
35: print*,'Unable to initialize PETSc'
36: stop
37: endif
39: ! The following MPI calls return the number of processes being used
40: ! and the rank of this process in the group.
42: call MPI_Comm_size(PETSC_COMM_WORLD,size,ierr)
43: call MPI_Comm_rank(PETSC_COMM_WORLD,rank,ierr)
45: ! Here we would like to print only one message that represents all
46: ! the processes in the group. Sleep so that IO from different ranks
47: ! don't get mixed up. Note this is not an ideal solution
48: call MPI_Comm_rank(MPI_COMM_WORLD,grank,ierr)
49: globalrank = grank
50: call PetscSleep(globalrank,ierr)
51: if (rank .eq. 0) write(6,100) size,rank
52: 100 format('No of Procs = ',i4,' rank = ',i4)
54: ! Always call PetscFinalize() before exiting a program. This
55: ! routine - finalizes the PETSc libraries as well as MPI - provides
56: ! summary and diagnostic information if certain runtime options are
57: ! chosen (e.g., -log_view). See PetscFinalize() manpage for more
58: ! information.
60: call PetscFinalize(ierr)
61: call MPI_Comm_free(PETSC_COMM_WORLD,ierr)
62: #if defined(PETSC_HAVE_ELEMENTAL)
63: call PetscElementalFinalizePackage(ierr)
64: #endif
66: ! Since we initialized MPI, we must call MPI_Finalize()
68: call MPI_Finalize(ierr)
69: end
71: !/*TEST
72: !
73: ! test:
74: ! nsize: 5
75: ! filter: sort -b
76: ! filter_output: sort -b
77: ! requires: !cuda !saws
78: !
79: !TEST*/