Actual source code: ex4f90.F90
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
17: integer ierr
18: integer rank, size
20: ! We must call MPI_Init() first, making us, not PETSc, responsible
21: ! for MPI
23: call MPI_Init(ierr)
24: if (ierr .ne. 0) then
25: print*,'Unable to initialize MPI'
26: stop
27: endif
29: ! We can now change the communicator universe for PETSc
31: call MPI_Comm_rank(MPI_COMM_WORLD,rank,ierr)
32: call MPI_Comm_split(MPI_COMM_WORLD,mod(rank,2),0,PETSC_COMM_WORLD,ierr)
34: ! Every PETSc routine should begin with the PetscInitialize()
35: ! routine.
37: call PetscInitialize(PETSC_NULL_CHARACTER,ierr)
38: if (ierr .ne. 0) then
39: print*,'Unable to initialize PETSc'
40: stop
41: endif
43: ! The following MPI calls return the number of processes being used
44: ! and the rank of this process in the group.
46: call MPI_Comm_size(PETSC_COMM_WORLD,size,ierr);CHKERRA(ierr)
47: call MPI_Comm_rank(PETSC_COMM_WORLD,rank,ierr);CHKERRA(ierr)
50: ! Here we would like to print only one message that represents all
51: ! the processes in the group.
52: if (rank .eq. 0) write(6,100) size,rank
53: 100 format('No of Procs = ',i4,' rank = ',i4)
55: ! Always call PetscFinalize() before exiting a program. This
56: ! routine - finalizes the PETSc libraries as well as MPI - provides
57: ! summary and diagnostic information if certain runtime options are
58: ! chosen (e.g., -log_view). See PetscFinalize() manpage for more
59: ! information.
61: call PetscFinalize(ierr)
62: call MPI_Comm_free(PETSC_COMM_WORLD,ierr)
64: ! Since we initialized MPI, we must call MPI_Finalize()
66: call MPI_Finalize(ierr)
67: end
69: !
70: !/*TEST
71: !
72: ! test:
73: !
74: !TEST*/