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

Actual source code: ex2.c
petsc-3.4.2 2013-07-02

      2: static char help[] = "Synchronized printing.\n\n";

      4: /*T
      5:    Concepts: petsc^introduction
      6:    Concepts: printing^synchronized
      7:    Concepts: printing^in parallel
      8:    Concepts: printf^synchronized
      9:    Concepts: printf^in parallel
     10:    Processors: n
     11: T*/

     13: #include <petscsys.h>
     14: int main(int argc,char **argv)
     15: {
     17:   PetscMPIInt    rank,size;

     19:   /*
     20:     Every PETSc program should begin with the PetscInitialize() routine.
     21:     argc, argv - These command line arguments are taken to extract the options
     22:                  supplied to PETSc and options supplied to MPI.
     23:     help       - When PETSc executable is invoked with the option -help,
     24:                  it prints the various options that can be applied at
     25:                  runtime.  The user can use the "help" variable place
     26:                  additional help messages in this printout.
     27:   */
     28:   PetscInitialize(&argc,&argv,NULL,help);

     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:   MPI_Comm_size(PETSC_COMM_WORLD,&size);
     35:   MPI_Comm_rank(PETSC_COMM_WORLD,&rank);

     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 representing PETSC_COMM_WORLD, i.e., all the processors.
     42:   */
     43:   PetscPrintf(PETSC_COMM_WORLD,"Number of processors = %d, rank = %d\n",size,rank);
     44:   /*
     45:      Here we would like to print info from each process, such that
     46:      output from process "n" appears after output from process "n-1".
     47:      To do this we use a combination of PetscSynchronizedPrintf() and
     48:      PetscSynchronizedFlush() with the communicator PETSC_COMM_WORLD.
     49:      All the processes print the message, one after another.
     50:      PetscSynchronizedFlush() indicates that the current process in the
     51:      given communicator has concluded printing, so that the next process
     52:      in the communicator can begin printing to the screen.
     53:      */
     54:   PetscSynchronizedPrintf(PETSC_COMM_WORLD,"[%d] Synchronized Hello World.\n",rank);
     55:   PetscSynchronizedPrintf(PETSC_COMM_WORLD,"[%d] Synchronized Hello World - Part II.\n",rank);
     56:   PetscSynchronizedFlush(PETSC_COMM_WORLD);
     57:   /*
     58:     Here a barrier is used to separate the two states.
     59:   */
     60:   MPI_Barrier(PETSC_COMM_WORLD);

     62:   /*
     63:     Here we simply use PetscPrintf() with the communicator PETSC_COMM_SELF
     64:     (where each process is considered separately).  Thus, this time the
     65:     output from different processes does not appear in any particular order.
     66:   */
     67:   PetscPrintf(PETSC_COMM_SELF,"[%d] Jumbled Hello World\n",rank);

     69:   /*
     70:      Always call PetscFinalize() before exiting a program.  This routine
     71:        - finalizes the PETSc libraries as well as MPI
     72:        - provides summary and diagnostic information if certain runtime
     73:          options are chosen (e.g., -log_summary).
     74:      See the PetscFinalize() manpage for more information.
     75:   */
     76:   PetscFinalize();
     77:   return 0;
     78: }