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*/

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

 15:   /*
 16:     Every PETSc program should begin with the PetscInitialize() routine.
 17:     argc, argv - These command line arguments are taken to extract the options
 18:                  supplied to PETSc and options supplied to MPI.
 19:     help       - When PETSc executable is invoked with the option -help,
 20:                  it prints the various options that can be applied at
 21:                  runtime.  The user can use the "help" variable to place
 22:                  additional help messages in this printout.
 23:   */
 24:   PetscInitialize(&argc,&argv,(char*)0,help);

 26:   /*
 27:      The following MPI calls return the number of processes
 28:      being used and the rank of this process in the group.
 29:    */
 30:   MPI_Comm_size(PETSC_COMM_WORLD,&size);
 31:   MPI_Comm_rank(PETSC_COMM_WORLD,&rank);

 33:   /*
 34:      Here we would like to print only one message that represents
 35:      all the processes in the group.  We use PetscPrintf() with the
 36:      communicator PETSC_COMM_WORLD.  Thus, only one message is
 37:      printed representng PETSC_COMM_WORLD, i.e., all the processors.
 38:   */
 39:   PetscPrintf(PETSC_COMM_WORLD,"Number of processors = %d, rank = %d\n",size,rank);

 41:   /*
 42:     Here a barrier is used to separate the two program states.
 43:   */
 44:   MPI_Barrier(PETSC_COMM_WORLD);

 46:   /*
 47:     Here we simply use PetscPrintf() with the communicator PETSC_COMM_SELF,
 48:     where each process is considered separately and prints independently
 49:     to the screen.  Thus, the output from different processes does not
 50:     appear in any particular order.
 51:   */

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

 55:   /*
 56:      Always call PetscFinalize() before exiting a program.  This routine
 57:        - finalizes the PETSc libraries as well as MPI
 58:        - provides summary and diagnostic information if certain runtime
 59:          options are chosen (e.g., -log_view).  See PetscFinalize()
 60:      manpage for more information.
 61:   */
 62:   PetscFinalize();
 63:   return 0;
 64: }

 66: /*TEST

 68:    test:

 70: TEST*/