Actual source code: ex4f90.F90
petsc-3.15.0 2021-03-30
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 petscmpi ! or mpi or mpi_f08
15: use petscsys
16: implicit none
18: PetscErrorCode ierr
19: PetscMPIInt rank, size, zero, two
21: ! We must call MPI_Init() first, making us, not PETSc, responsible
22: ! for MPI
24: call MPI_Init(ierr)
25: if (ierr .ne. 0) then
26: print*,'Unable to initialize MPI'
27: stop
28: endif
30: ! We can now change the communicator universe for PETSc
32: zero = 0
33: two = 2
34: call MPI_Comm_rank(MPI_COMM_WORLD,rank,ierr)
35: call MPI_Comm_split(MPI_COMM_WORLD,mod(rank,two),zero,PETSC_COMM_WORLD,ierr)
37: ! Every PETSc routine should begin with the PetscInitialize()
38: ! routine.
40: call PetscInitialize(PETSC_NULL_CHARACTER,ierr)
41: if (ierr .ne. 0) then
42: print*,'Unable to initialize PETSc'
43: stop
44: endif
46: ! The following MPI calls return the number of processes being used
47: ! and the rank of this process in the group.
49: call MPI_Comm_size(PETSC_COMM_WORLD,size,ierr);CHKERRA(ierr)
50: call MPI_Comm_rank(PETSC_COMM_WORLD,rank,ierr);CHKERRA(ierr)
53: ! Here we would like to print only one message that represents all
54: ! the processes in the group.
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)
67: ! Since we initialized MPI, we must call MPI_Finalize()
69: call MPI_Finalize(ierr)
70: end
72: !
73: !/*TEST
74: !
75: ! test:
76: !
77: !TEST*/