Date: 2013-07-02T14:39:25+00:00

Actual source code: ex1.c
petsc-3.4.2 2013-07-02

      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*/

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

     16:   /*
     17:     Every PETSc routine should begin with the PetscInitialize() routine.
     18:     argc, argv - These command line arguments are taken to extract the options
     19:                  supplied to PETSc and options supplied to MPI.
     20:     help       - When PETSc executable is invoked with the option -help,
     21:                  it prints the various options that can be applied at
     22:                  runtime.  The user can use the "help" variable place
     23:                  additional help messages in this printout.
     24:   */
     25:   PetscInitialize(&argc,&argv,(char*)0,help);

     27:   /*
     28:      The following MPI calls return the number of processes
     29:      being used and the rank of this process in the group.
     30:    */
     31:   MPI_Comm_size(PETSC_COMM_WORLD,&size);
     32:   MPI_Comm_rank(PETSC_COMM_WORLD,&rank);

     34:   /*
     35:      Here we would like to print only one message that represents
     36:      all the processes in the group.  We use PetscPrintf() with the
     37:      communicator PETSC_COMM_WORLD.  Thus, only one message is
     38:      printed representng PETSC_COMM_WORLD, i.e., all the processors.
     39:   */
     40:   PetscPrintf(PETSC_COMM_WORLD,"Number of processors = %d, rank = %d\n",size,rank);

     42:   /*
     43:     Here a barrier is used to separate the two program states.
     44:   */
     45:   MPI_Barrier(PETSC_COMM_WORLD);

     47:   /*
     48:     Here we simply use PetscPrintf() with the communicator PETSC_COMM_SELF,
     49:     where each process is considered separately and prints independently
     50:     to the screen.  Thus, the output from different processes does not
     51:     appear in any particular order.
     52:   */

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

     56:   /*
     57:      Always call PetscFinalize() before exiting a program.  This routine
     58:        - finalizes the PETSc libraries as well as MPI
     59:        - provides summary and diagnostic information if certain runtime
     60:          options are chosen (e.g., -log_summary).  See PetscFinalize()
     61:      manpage for more information.
     62:   */
     63:   PetscFinalize();
     64:   return 0;
     65: }