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: PetscCallMPIA(MPI_Init(ierr))
21: ! We can now change the communicator universe for PETSc
23: zero = 0
24: two = 2
25: PetscCallMPIA(MPI_Comm_rank(MPI_COMM_WORLD,rank,ierr))
26: PetscCallMPIA(MPI_Comm_split(MPI_COMM_WORLD,mod(rank,two),zero,PETSC_COMM_WORLD,ierr))
28: ! Every PETSc routine should begin with the PetscInitialize()
29: ! routine.
31: PetscCallA(PetscInitialize(ierr))
33: ! The following MPI calls return the number of processes being used
34: ! and the rank of this process in the group.
36: PetscCallMPIA(MPI_Comm_size(PETSC_COMM_WORLD,size,ierr))
37: PetscCallMPIA(MPI_Comm_rank(PETSC_COMM_WORLD,rank,ierr))
39: ! Here we would like to print only one message that represents all
40: ! the processes in the group.
41: if (rank .eq. 0) write(6,100) size,rank
42: 100 format('No of Procs = ',i4,' rank = ',i4)
44: ! Always call PetscFinalize() before exiting a program. This
45: ! routine - finalizes the PETSc libraries as well as MPI - provides
46: ! summary and diagnostic information if certain runtime options are
47: ! chosen (e.g., -log_view). See PetscFinalize() manpage for more
48: ! information.
50: PetscCallA(PetscFinalize(ierr))
51: PetscCallMPIA(MPI_Comm_free(PETSC_COMM_WORLD,ierr))
53: ! Since we initialized MPI, we must call MPI_Finalize()
55: PetscCallMPIA(MPI_Finalize(ierr))
56: end
58: !
59: !/*TEST
60: !
61: ! test:
62: !
63: !TEST*/