Date: 2013-07-02T14:39:26+00:00

Actual source code: ex4.c
petsc-3.4.2 2013-07-02

      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
      7: T*/
      8:  #include <petscsys.h>

     10: int main(int argc, char *argv[])
     11: {
     13:   PetscMPIInt    rank, size;

     15:   /* We must call MPI_Init() first, making us, not PETSc, responsible for MPI */
     16:   MPI_Init(&argc, &argv);

     18:   /* We can now change the communicator universe for PETSc */
     19:   MPI_Comm_rank(MPI_COMM_WORLD, &rank);
     20:   MPI_Comm_split(MPI_COMM_WORLD, rank%2, 0, &PETSC_COMM_WORLD);

     22:   /*
     23:     Every PETSc routine should begin with the PetscInitialize() routine.
     24:     argc, argv - These command line arguments are taken to extract the options
     25:                  supplied to PETSc and options supplied to MPI.
     26:     help       - When PETSc executable is invoked with the option -help,
     27:                  it prints the various options that can be applied at
     28:                  runtime.  The user can use the "help" variable place
     29:                  additional help messages in this printout.
     30:   */
     31:   PetscInitialize(&argc, &argv, (char*) 0, help);

     33:   /*
     34:      The following MPI calls return the number of processes
     35:      being used and the rank of this process in the group.
     36:    */
     37:   MPI_Comm_size(PETSC_COMM_WORLD,&size);
     38:   MPI_Comm_rank(PETSC_COMM_WORLD,&rank);

     40:   /*
     41:      Here we would like to print only one message that represents
     42:      all the processes in the group.  We use PetscPrintf() with the
     43:      communicator PETSC_COMM_WORLD.  Thus, only one message is
     44:      printed representng PETSC_COMM_WORLD, i.e., all the processors.
     45:   */
     46:   PetscPrintf(PETSC_COMM_WORLD,"Number of processors = %d, rank = %d\n", size, rank);

     48:   /*
     49:      Always call PetscFinalize() before exiting a program.  This routine
     50:        - finalizes the PETSc libraries as well as MPI
     51:        - provides summary and diagnostic information if certain runtime
     52:          options are chosen (e.g., -log_summary).  See PetscFinalize()
     53:      manpage for more information.
     54:   */
     55:   PetscFinalize();

     57:   /* Since we initialized MPI, we must call MPI_Finalize() */
     58:   MPI_Finalize();
     59:   return 0;
     60: }