Date: 2022-03-31T04:46:16+00:00

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*/