Didasko Development
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// ***********************************************************************
// 
//                      Didasko Tutorial Package
//                 Copyright (2005) Sandia Corporation
// 
// Under terms of Contract DE-AC04-94AL85000, there is a non-exclusive
// license for use of this work by or on behalf of the U.S. Government.
// 
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// modification, are permitted provided that the following conditions are
// met:
//
// 1. Redistributions of source code must retain the above copyright
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// Questions about Didasko? Contact Marzio Sala (marzio.sala _AT_ gmail.com)
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// @HEADER

// Basic definition of communicator.
// This code should be run with at least two processes
// However, note that the SAME code works even if Epetra
// has been configured without MPI!

#include "Didasko_ConfigDefs.h"
#if defined(HAVE_DIDASKO_EPETRA)

#include "Epetra_ConfigDefs.h"
#ifdef HAVE_MPI
#include "mpi.h"
#include "Epetra_MpiComm.h"
#else
#include "Epetra_SerialComm.h"
#endif

int main(int argc, char *argv[])
{

#ifdef HAVE_MPI
  MPI_Init(&argc, &argv);
  // define an Epetra communicator
  Epetra_MpiComm Comm(MPI_COMM_WORLD);
#else
  Epetra_SerialComm Comm;
#endif

  // get the proc ID of this process
  int MyPID = Comm.MyPID();
  
  // get the total number of processes
  int NumProc = Comm.NumProc();
  
  // output some information to std output
  cout << Comm << endl;
  
  // ======================== //
  // now some basic MPI calls //
  // ------------------------ //
  
  int    ivalue;
  double dvalue, dvalue2;
  double* dvalues;  dvalues  = new double[NumProc];
  double* dvalues2; dvalues2 = new double[NumProc];
  int root = 0;
  
  // equivalent to MPI_Barrier
  
  Comm.Barrier();
   
  if (MyPID == root) dvalue = 12.0;

  // On input, the root processor contains the list of values
  // (in this case, a single value). On exit, all processes will
  // have he same list of values. Note that all values must be allocated
  // vefore the broadcast
  
  // equivalent to  MPI_Broadcast
    
  Comm.Broadcast(&dvalue, 1, root);

  // as before, but with integer values. As C++ can bind to the appropriate
  // interface based on argument typing, the type of data is not required.
  
  Comm.Broadcast(&ivalue, 1, root);

  // equivalent MPI_Allgather

  Comm.GatherAll(dvalues, dvalues2, 1);

  // equivalent to MPI_Allreduce with MPI_SUM

  dvalue = 1.0*MyPID;

  Comm.SumAll( &dvalue, dvalues, 1);

  // equivalent to MPI_Allreduce with MPI_SUM

  Comm.MaxAll( &dvalue, dvalues, 1);

  // equiavant to MPI_Scan with MPI_SUM

  dvalue = 1.0 * MyPID;
  
  Comm.ScanSum(&dvalue, &dvalue2, 1);

  cout << "On proc " << MyPID << " dvalue2  = " << dvalue2 << endl;
  
  delete[] dvalues;
  delete[] dvalues2;

  // ======================= //
  // Finalize MPI and return //
  // ----------------------- //
    
#ifdef HAVE_MPI
  MPI_Finalize();
#endif

  return( EXIT_SUCCESS );
  
} /* main */

#else

#include <stdlib.h>
#include <stdio.h>
#ifdef HAVE_MPI
#include "mpi.h"
#endif

int main(int argc, char *argv[])
{
#ifdef HAVE_MPI
  MPI_Init(&argc,&argv);
#endif

  puts("Please configure Didasko with:\n"
       "--enable-epetra");

#ifdef HAVE_MPI
  MPI_Finalize();
#endif
  return 0;
}
#endif

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