1: static char help[] = "Introductory example that illustrates printing.\n\n";

  3: #include <petscsys.h>
  4: int main(int argc, char **argv)
  5: {
  6:   PetscMPIInt rank, size;

  8:   /*
  9:     Every PETSc program should begin with the PetscInitialize() routine.
 10:     argc, argv - These command line arguments are taken to extract the options
 11:                  supplied to PETSc and options supplied to MPI.
 12:     help       - When PETSc executable is invoked with the option -help,
 13:                  it prints the various options that can be applied at
 14:                  runtime.  The user can use the "help" variable to place
 15:                  additional help messages in this printout.
 16:   */
 17:   PetscFunctionBeginUser;
 18:   PetscCall(PetscInitialize(&argc, &argv, (char *)0, help));

 20:   /*
 21:      The following MPI calls return the number of processes
 22:      being used and the rank of this process in the group.
 23:    */
 24:   PetscCallMPI(MPI_Comm_size(PETSC_COMM_WORLD, &size));
 25:   PetscCallMPI(MPI_Comm_rank(PETSC_COMM_WORLD, &rank));

 27:   /*
 28:      Here we would like to print only one message that represents
 29:      all the processes in the group.  We use PetscPrintf() with the
 30:      communicator PETSC_COMM_WORLD.  Thus, only one message is
 31:      printed representng PETSC_COMM_WORLD, i.e., all the processors.
 32:   */
 33:   PetscCall(PetscPrintf(PETSC_COMM_WORLD, "Number of processors = %d, rank = %d\n", size, rank));

 35:   /*
 36:     Here a barrier is used to separate the two program states.
 37:   */
 38:   PetscCallMPI(MPI_Barrier(PETSC_COMM_WORLD));

 40:   /*
 41:     Here we simply use PetscPrintf() with the communicator PETSC_COMM_SELF,
 42:     where each process is considered separately and prints independently
 43:     to the screen.  Thus, the output from different processes does not
 44:     appear in any particular order.
 45:   */

 47:   PetscCall(PetscPrintf(PETSC_COMM_SELF, "[%d] Jumbled Hello World\n", rank));

 49:   /*
 50:      Always call PetscFinalize() before exiting a program.  This routine
 51:        - finalizes the PETSc libraries as well as MPI
 52:        - provides summary and diagnostic information if certain runtime
 53:          options are chosen (e.g., -log_view).  See PetscFinalize()
 54:      manpage for more information.
 55:   */
 56:   PetscCall(PetscFinalize());
 57:   return 0;
 58: }

 60: /*TEST

 62:    test:

 64: TEST*/