Actual source code: ex4.c
1: static char help = "Introductory example that illustrates running PETSc on a subset of processes.\n\n";
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.
11: #include <petscsys.h>
13: int main(int argc, char *argv)
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;
21: /* We can now change the communicator universe for PETSc */
22: MPI_Comm_rank(MPI_COMM_WORLD, &rank);if (ierr) return ierr;
23: MPI_Comm_split(MPI_COMM_WORLD, rank%2, 0, &PETSC_COMM_WORLD);if (ierr) return ierr;
26: Every PETSc routine should begin with the PetscInitialize() routine.
27: argc, argv - These command line arguments are taken to extract the options
28: supplied to PETSc and options supplied to MPI.
29: help - When PETSc executable is invoked with the option -help,
30: it prints the various options that can be applied at
31: runtime. The user can use the "help" variable place
32: additional help messages in this printout.
34: PetscInitialize(&argc, &argv, (char*) 0, help);if (ierr) return ierr;
37: The following MPI calls return the number of processes
38: being used and the rank of this process in the group.
44: Here we would like to print only one message that represents
45: all the processes in the group. We use PetscPrintf() with the
46: communicator PETSC_COMM_WORLD. Thus, only one message is
47: printed representng PETSC_COMM_WORLD, i.e., all the processors.
49: PetscPrintf(PETSC_COMM_WORLD,"Number of processors = %d, rank = %d\n", size, rank);
52: Always call PetscFinalize() before exiting a program. This routine
53: - finalizes the PETSc libraries as well as MPI
54: - provides summary and diagnostic information if certain runtime
55: options are chosen (e.g., -log_view). See PetscFinalize()
56: manpage for more information.
58: PetscFinalize();if (ierr) return ierr;
60: MPI_Comm_free(&PETSC_COMM_WORLD);if (ierr) return ierr;
61: /* Since we initialized MPI, we must call MPI_Finalize() */
63: return ierr;
70: nsize: 5
71: args: -options_left no
72: filter: sort -b | grep -v saws_port_auto_selectcd
73: filter_output: sort -b