Actual source code: ex4f.F
petsc-3.13.6 2020-09-29
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)
24: #if defined(PETSC_HAVE_ELEMENTAL)
25: call PetscElementalInitializePackage(ierr)
26: #endif
27: ! We can now change the communicator universe for PETSc
29: two = 2
30: call MPI_Comm_rank(MPI_COMM_WORLD,rank,ierr)
31: call MPI_Comm_split(MPI_COMM_WORLD,mod(rank,two),0, &
32: & PETSC_COMM_WORLD,ierr)
34: ! Every PETSc routine should begin with the PetscInitialize()
35: ! routine.
36: call PetscInitializeNoArguments(ierr)
37: if (ierr .ne. 0) then
38: print*,'Unable to initialize PETSc'
39: stop
40: endif
42: ! The following MPI calls return the number of processes being used
43: ! and the rank of this process in the group.
45: call MPI_Comm_size(PETSC_COMM_WORLD,size,ierr)
46: call MPI_Comm_rank(PETSC_COMM_WORLD,rank,ierr)
49: ! Here we would like to print only one message that represents all
50: ! the processes in the group. Sleep so that IO from different ranks
51: ! don't get mixed up. Note this is not an ideal solution
52: call MPI_Comm_rank(MPI_COMM_WORLD,grank,ierr)
53: globalrank = grank
54: call PetscSleep(globalrank,ierr)
55: if (rank .eq. 0) write(6,100) size,rank
56: 100 format('No of Procs = ',i4,' rank = ',i4)
58: ! Always call PetscFinalize() before exiting a program. This
59: ! routine - finalizes the PETSc libraries as well as MPI - provides
60: ! summary and diagnostic information if certain runtime options are
61: ! chosen (e.g., -log_view). See PetscFinalize() manpage for more
62: ! information.
64: call PetscFinalize(ierr)
65: call MPI_Comm_free(PETSC_COMM_WORLD,ierr)
66: #if defined(PETSC_HAVE_ELEMENTAL)
67: call PetscElementalFinalizePackage(ierr)
68: #endif
71: ! Since we initialized MPI, we must call MPI_Finalize()
73: call MPI_Finalize(ierr)
74: end
76: !/*TEST
77: !
78: ! test:
79: ! nsize: 5
80: ! filter: sort -b
81: ! filter_output: sort -b
82: ! requires: !cuda
83: !
84: !TEST*/