/* -----------------------------------------------------------------------
 
    split-c.soln.c
    Lab solution for MPI Groups and Communicator Management
 
    There are 2 parts to the project:
         1.  Build 2 communicators, one for even-numbered tasks
             (starting with task 0), one for odd-numbered tasks.
         2.  Do a sum reduction over each communicator.
 
    AUTHOR: S. Hotovy 12/95
    REVISED: R. Leibensperger 4/96

  -------------------------------------------------------------------- */
#include <stdio.h>
#include <stddef.h>
#include <stdlib.h>
#include <math.h>
#include "mpi.h"

      main(int argc, char **argv)
{
      int rank_in_world, rank_in_newcomm, color;
      MPI_Comm newcomm;
      float xsin, xsum;
      FILE *fdesc;
      char fname[13], *gname[2];
      gname[0]="even";
      gname[1]="odd";

      MPI_Init(&argc, &argv);
/*
   ==============================================
     Establish rank of this task in MPI_COMM_WORLD
   ==============================================
*/
      MPI_Comm_rank(MPI_COMM_WORLD,&rank_in_world);
/*
   ====================================================================
     Project:  Assign the variable color a different value for even 
               and odd tasks, then split MPI_COMM_WORLD based on color.
               Store the new communicator in the variable newcomm
   ====================================================================
*/
      /*  =====>  Put code here */
      if ((rank_in_world % 2) == 0) color = 0;
      else color = 1;
      MPI_Comm_split (MPI_COMM_WORLD, color, rank_in_world, &newcomm);

      xsin = fabs(sin(151.*(float)(rank_in_world+10)));
/*
  ================================================================
    Project: Sum all values of xsin within each communicator

    First:   Accummulate the sum of the values of xsin across the 
             communicator, store as xsum on the task with rank 0
    Second:  Learn your rank in the new communicator and assign to
             the variable rank_in_newcomm.  The task with rank 0
	     will print the results
  ================================================================
*/
      /*  =====>  Put code here */
      MPI_Reduce(&xsin,&xsum,1,MPI_FLOAT,MPI_SUM,0,newcomm);
      MPI_Comm_rank (newcomm, &rank_in_newcomm);

      if (rank_in_newcomm == 0)  {
	sprintf (fname, "%s.rep", gname[color]);
	fdesc = fopen(fname,"w");
	fprintf(fdesc,"Sum of %s tasks: %12.5f\n",gname[color], xsum);
	fclose (fdesc);  }
      
      MPI_Finalize();
}