Actual source code: ex4f90.F90
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
17: PetscErrorCode ierr
18: PetscMPIInt rank, size, two
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: two = 2
32: call MPI_Comm_rank(MPI_COMM_WORLD,rank,ierr)
33: call MPI_Comm_split(MPI_COMM_WORLD,mod(rank,two),0,PETSC_COMM_WORLD,ierr)
35: ! Every PETSc routine should begin with the PetscInitialize()
36: ! routine.
38: call PetscInitialize(PETSC_NULL_CHARACTER,ierr)
39: if (ierr .ne. 0) then
40: print*,'Unable to initialize PETSc'
41: stop
42: endif
44: ! The following MPI calls return the number of processes being used
45: ! and the rank of this process in the group.
47: call MPI_Comm_size(PETSC_COMM_WORLD,size,ierr);CHKERRA(ierr)
48: call MPI_Comm_rank(PETSC_COMM_WORLD,rank,ierr);CHKERRA(ierr)
51: ! Here we would like to print only one message that represents all
52: ! the processes in the group.
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)
63: call MPI_Comm_free(PETSC_COMM_WORLD,ierr)
65: ! Since we initialized MPI, we must call MPI_Finalize()
67: call MPI_Finalize(ierr)
68: end
70: !
71: !/*TEST
72: !
73: ! test:
74: !
75: !TEST*/