Actual source code: ex1.c

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

      4: /*T
      5:    Concepts: introduction to PETSc;
      6:    Concepts: printing^in parallel
      7:    Processors: n
      8: T*/

     12: #include <petscsys.h>
     13: int main(int argc,char **argv)
     14: {
     16:   PetscMPIInt    rank,size;

     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:   PetscInitialize(&argc,&argv,(char*)0,help);if (ierr) return ierr;

     29:   /*
     30:      The following MPI calls return the number of processes
     31:      being used and the rank of this process in the group.
     32:    */
     33:   MPI_Comm_size(PETSC_COMM_WORLD,&size);
     34:   MPI_Comm_rank(PETSC_COMM_WORLD,&rank);

     36:   /*
     37:      Here we would like to print only one message that represents
     38:      all the processes in the group.  We use PetscPrintf() with the
     39:      communicator PETSC_COMM_WORLD.  Thus, only one message is
     40:      printed representng PETSC_COMM_WORLD, i.e., all the processors.
     41:   */
     42:   PetscPrintf(PETSC_COMM_WORLD,"Number of processors = %d, rank = %d\n",size,rank);

     44:   /*
     45:     Here a barrier is used to separate the two program states.
     46:   */
     47:   MPI_Barrier(PETSC_COMM_WORLD);

     49:   /*
     50:     Here we simply use PetscPrintf() with the communicator PETSC_COMM_SELF,
     51:     where each process is considered separately and prints independently
     52:     to the screen.  Thus, the output from different processes does not
     53:     appear in any particular order.
     54:   */

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

     58:   /*
     59:      Always call PetscFinalize() before exiting a program.  This routine
     60:        - finalizes the PETSc libraries as well as MPI
     61:        - provides summary and diagnostic information if certain runtime
     62:          options are chosen (e.g., -log_view).  See PetscFinalize()
     63:      manpage for more information.
     64:   */
     65:   PetscFinalize();
     66:   return ierr;
     67: }

     70: /*TEST

     72:    test:

     74: TEST*/