1 static char help[] = "Introductory example that illustrates running PETSc on a subset of processes.\n\n";
2
3 #include <petscsys.h>
4
main(int argc,char * argv[])5 int main(int argc, char *argv[])
6 {
7 PetscMPIInt rank, size;
8
9 /* We must call MPI_Init() first, making us, not PETSc, responsible for MPI */
10 PetscCallMPI(MPI_Init(&argc, &argv));
11 #if defined(PETSC_HAVE_ELEMENTAL)
12 PetscCall(PetscElementalInitializePackage());
13 #endif
14 /* We can now change the communicator universe for PETSc */
15 PetscCallMPI(MPI_Comm_rank(MPI_COMM_WORLD, &rank));
16 PetscCallMPI(MPI_Comm_split(MPI_COMM_WORLD, rank % 2, 0, &PETSC_COMM_WORLD));
17
18 /*
19 Every PETSc routine should begin with the PetscInitialize() routine.
20 argc, argv - These command line arguments are taken to extract the options
21 supplied to PETSc and options supplied to MPI.
22 help - When PETSc executable is invoked with the option -help,
23 it prints the various options that can be applied at
24 runtime. The user can use the "help" variable place
25 additional help messages in this printout.
26 */
27 PetscFunctionBeginUser;
28 PetscCall(PetscInitialize(&argc, &argv, NULL, help));
29
30 /*
31 The following MPI calls return the number of processes
32 being used and the rank of this process in the group.
33 */
34 PetscCallMPI(MPI_Comm_size(PETSC_COMM_WORLD, &size));
35 PetscCallMPI(MPI_Comm_rank(PETSC_COMM_WORLD, &rank));
36
37 /*
38 Here we would like to print only one message that represents
39 all the processes in the group. We use PetscPrintf() with the
40 communicator PETSC_COMM_WORLD. Thus, only one message is
41 printed representng PETSC_COMM_WORLD, i.e., all the processors.
42 */
43 PetscCall(PetscPrintf(PETSC_COMM_WORLD, "Number of processors = %d, rank = %d\n", size, rank));
44
45 /*
46 Always call PetscFinalize() before exiting a program. This routine
47 - finalizes the PETSc libraries as well as MPI
48 - provides summary and diagnostic information if certain runtime
49 options are chosen (e.g., -log_view). See PetscFinalize()
50 manpage for more information.
51 */
52 PetscCall(PetscFinalize());
53 PetscCallMPI(MPI_Comm_free(&PETSC_COMM_WORLD));
54 #if defined(PETSC_HAVE_ELEMENTAL)
55 PetscCall(PetscElementalFinalizePackage());
56 #endif
57 /* Since we initialized MPI, we must call MPI_Finalize() */
58 PetscCallMPI(MPI_Finalize());
59 return 0;
60 }
61
62 /*TEST
63
64 test:
65 nsize: 5
66 args: -options_left no
67 filter: sort -b | grep -v saws_port_auto_selectcd
68 filter_output: sort -b
69
70 TEST*/
71