/************************************************************
  File:          cholesky_slave.cc                              
  Description:   A program that inputs a matrix from a file 
                 and computes the Cholesky decomposition 
		 using several processes.
                                                         
  Author:        Dana Vrajitoru                          
  Organization:  IUSB                                    
  Date:          August 16, 2002                           
**************************************************************/

#include <mpi.h>
#include <stdlib.h>
#include <iostream.h>
#include <math.h>
#include "cholesky_slave.h"
#include "common.h"

// The core function that computes the Cholesky decomposition.
void Compute_cholesky(int proc_id, int proc_number)      
{ 
  int l, k, size=proc_number-1, col = proc_id-1;
  float x, *ai, ak, *a_proc;
  ai = new float[size];
  a_proc = new float[size];

  Receive_float_array(MASTER_ID, a_proc, size);

  for (l=0; l<=2*size-2; l++) {
    if ((l<=2*col) && (col <= min(l, size-1))) {
      x = a_proc[l-col];
      if (l != 2*col) 
        Receive_float_array(l-col+1, ai, l-col+1);
      for (k=0; k<l-col; k++) {
	if (l == 2*col)
          ak = a_proc[k];
        else
          ak = ai[k];
        x -= a_proc[k] * ak;
      }
      if (l == 2*col)
        a_proc[l-col] = sqrt(x);
      else
        a_proc[l-col] = x / ai[l-proc_id+1];
    }
    else if ((2*col < l) && (l-col <= min(l, size-1)))
      Send_float_array(l-col+1, a_proc, col+1);
  }

  Send_float_array(MASTER_ID, a_proc, col+1);
}