Actual source code: ex4.c
petsc-3.13.6 2020-09-29
1: static char help[] = "Introductory example that illustrates running PETSc on a subset of processes.\n\n";
3: /*T
4: Concepts: introduction to PETSc;
5: Concepts: process^subset set PETSC_COMM_WORLD
6: Processors: 2
8: Note that this example is not checking the error codes from the MPI calls with CHKERRQ() before PETSc is initialized
9: and after PETSc is finalized. This is because the PETSc macro CHKERRQ() will not work in those circumstances.
10: T*/
11: #include <petscsys.h>
13: int main(int argc, char *argv[])
14: {
16: PetscMPIInt rank, size;
18: /* We must call MPI_Init() first, making us, not PETSc, responsible for MPI */
19: MPI_Init(&argc, &argv);if (ierr) return ierr;
20: #if defined(PETSC_HAVE_ELEMENTAL)
21: PetscElementalInitializePackage();if (ierr) return ierr;
22: #endif
23: /* We can now change the communicator universe for PETSc */
24: MPI_Comm_rank(MPI_COMM_WORLD, &rank);if (ierr) return ierr;
25: MPI_Comm_split(MPI_COMM_WORLD, rank%2, 0, &PETSC_COMM_WORLD);if (ierr) return ierr;
27: /*
28: Every PETSc routine should begin with the PetscInitialize() routine.
29: argc, argv - These command line arguments are taken to extract the options
30: supplied to PETSc and options supplied to MPI.
31: help - When PETSc executable is invoked with the option -help,
32: it prints the various options that can be applied at
33: runtime. The user can use the "help" variable place
34: additional help messages in this printout.
35: */
36: PetscInitialize(&argc, &argv, (char*) 0, help);if (ierr) return ierr;
38: /*
39: The following MPI calls return the number of processes
40: being used and the rank of this process in the group.
41: */
42: MPI_Comm_size(PETSC_COMM_WORLD,&size);
43: MPI_Comm_rank(PETSC_COMM_WORLD,&rank);
45: /*
46: Here we would like to print only one message that represents
47: all the processes in the group. We use PetscPrintf() with the
48: communicator PETSC_COMM_WORLD. Thus, only one message is
49: printed representng PETSC_COMM_WORLD, i.e., all the processors.
50: */
51: PetscPrintf(PETSC_COMM_WORLD,"Number of processors = %d, rank = %d\n", size, rank);
53: /*
54: Always call PetscFinalize() before exiting a program. This routine
55: - finalizes the PETSc libraries as well as MPI
56: - provides summary and diagnostic information if certain runtime
57: options are chosen (e.g., -log_view). See PetscFinalize()
58: manpage for more information.
59: */
60: PetscFinalize();if (ierr) return ierr;
61: MPI_Comm_free(&PETSC_COMM_WORLD);if (ierr) return ierr;
62: #if defined(PETSC_HAVE_ELEMENTAL)
63: PetscElementalFinalizePackage();if (ierr) return ierr;
64: #endif
65: /* Since we initialized MPI, we must call MPI_Finalize() */
66: MPI_Finalize();
67: return ierr;
68: }
71: /*TEST
73: test:
74: nsize: 5
75: args: -options_left no
76: filter: sort -b | grep -v saws_port_auto_selectcd
77: filter_output: sort -b
79: TEST*/