Actual source code: ex4f.F
petsc-3.10.5 2019-03-28
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
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: call MPI_Comm_rank(MPI_COMM_WORLD,rank,ierr)
28: call MPI_Comm_split(MPI_COMM_WORLD,mod(rank,2),0, &
29: & PETSC_COMM_WORLD,ierr)
31: ! Every PETSc routine should begin with the PetscInitialize()
32: ! routine.
34: call PetscInitializeNoArguments(ierr)
35: if (ierr .ne. 0) then
36: print*,'Unable to initialize PETSc'
37: stop
38: endif
40: ! The following MPI calls return the number of processes being used
41: ! and the rank of this process in the group.
43: call MPI_Comm_size(PETSC_COMM_WORLD,size,ierr)
44: call MPI_Comm_rank(PETSC_COMM_WORLD,rank,ierr)
47: ! Here we would like to print only one message that represents all
48: ! the processes in the group. Sleep so that IO from different ranks
49: ! don't get mixed up. Note this is not an ideal solution
50: call MPI_Comm_rank(MPI_COMM_WORLD,grank,ierr)
51: globalrank = grank
52: call PetscSleep(globalrank,ierr)
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)
64: call MPI_Comm_free(PETSC_COMM_WORLD,ierr)
67: ! Since we initialized MPI, we must call MPI_Finalize()
69: call MPI_Finalize(ierr)
70: end
72: !/*TEST
73: !
74: ! test:
75: ! nsize: 5
76: ! filter: sort -b
77: ! filter_output: sort -b
78: !
79: !TEST*/