// ------------------------------------------------------------------------
// File: bound_pe.c
//
// Union bound on the word error probability of a binary linear code with
// transmission over a binary symmetric channel
// ------------------------------------------------------------------------
// This program is complementary material for the book:
//
// R.H. Morelos-Zaragoza, The Art of Error Correcting Coding, Wiley, 2002.
//
// ISBN 0471 49581 6
//
// This and other programs are available at http://the-art-of-ecc.com
//
// You may use this program for academic and personal purposes only. 
// If this program is used to perform simulations whose results are 
// published in a journal or book, please refer to the book above.
//
// The use of this program in a commercial product requires explicit
// written permission from the author. The author is not responsible or 
// liable for damage or loss that may be caused by the use of this program. 
//
// Copyright (c) 2002. Robert H. Morelos-Zaragoza. All rights reserved.
// ------------------------------------------------------------------------

#include <stdio.h>
#include <math.h>

#define NMAX 1024          // Maximum code length 

main(argc,argv)
int argc;
char **argv;
{
  int n;
  int t;
  double a[NMAX+1];        // Weight distribution
  double p, Pc;
  int i;
  double nd, id;

  double fact(double a);
  double comb(double a, double b);

  char name1[80], name2[80];
  FILE *fp1,*fp2;

  if (argc != 4)
  {
    printf("Usage: %s n t file_Pe\n",
    argv[0]);
    exit(1);
  }
  sscanf(argv[1], "%d", &n);
  sscanf(argv[2], "%d", &t);
  sscanf(argv[3], "%s", name1);

  fp1 = fopen(name1,"w");

  p = 1.0e-05;
  while (p<0.5)
    {
    Pc = 0.0;
    for (i=0; i<=t; i++)
      {
      nd = (double) n;
      id = (double) i;
      Pc += comb(nd,id) * pow(p,id)*pow((1.0-p),(nd-id));
      }
    fprintf(fp1,"%e %e\n", p, 1.0-Pc);
    p += 1.0e-05;
    }

}

double fact(double a)
{
    double i,tot;

    tot = 1.0;
    for (i=a;i>0.001;i=i-1.0)
    {
        tot = tot * i;
    }
    return(tot);
}

double comb(double a,double b)
{
    double z,tot;

        if (a<b)
           return(1.0);
    if (b > (a-b))
    {
       tot = 1.0/fact(a-b);
       for (z=a;z>b;z=z-1.0)
       {
          tot = tot * z;
       }
    }
    else
    {
       tot = 1.0/fact(b);
       for (z=a;z>a-b;z=z-1.0)
       {
          tot = tot * z;
       }
    }
    return(tot);
}