text: /* -*- Mode: C; c-basic-offset:4 ; -*- */
  /*
   *  (C) 2001 by Argonne National Laboratory.
   *      See COPYRIGHT in top-level directory.
   */
  #include "mpi.h"
  #include <stdio.h>
  #define BAD_ANSWER 100000
  
  int assoc ( int *, int *, int *, MPI_Datatype * );
  
  /*
      The operation is inoutvec[i] = invec[i] op inoutvec[i] 
      (see 4.9.4).  The order is important.
  
      Note that the computation is in process rank (in the communicator)
      order, independant of the root.
   */
  int assoc(int *invec, int *inoutvec, int *len, MPI_Datatype *dtype)
  {
    int i;
    for ( i=0; i<*len; i++ )  {
      if (inoutvec[i] <= invec[i] ) {
        int rank;
        MPI_Comm_rank( MPI_COMM_WORLD, &rank );
        fprintf( stderr, "[%d] inout[0] = %d, in[0] = %d\n", 
  	       rank, inoutvec[0], invec[0] );
        inoutvec[i] = BAD_ANSWER;
        }
      else 
        inoutvec[i] = invec[i];
    }
    return (1);
  }
  
  int main( int argc, char **argv )
  {
      int              rank, size;
      int              data;
      int              errors=0;
      int              result = -100;
      MPI_Op           op;
  
      MPI_Init( &argc, &argv );
      MPI_Comm_rank( MPI_COMM_WORLD, &rank );
      MPI_Comm_size( MPI_COMM_WORLD, &size );
  
      data = rank;
  
      MPI_Op_create( (MPI_User_function*)assoc, 0, &op );
      MPI_Reduce ( &data, &result, 1, MPI_INT, op, size-1, MPI_COMM_WORLD );
      MPI_Bcast  ( &result, 1, MPI_INT, size-1, MPI_COMM_WORLD );
      MPI_Op_free( &op );
      if (result == BAD_ANSWER) errors++;
  
      if (errors)
        printf( "[%d] done with ERRORS(%d)!\n", rank, errors );
      else {
  	if (rank == 0) 
  	    printf(" No Errors\n");
      }
  
      MPI_Finalize();
  
      return errors;
  }
  