#!/usr/bin/perl

# Perl script: MonteCarlo.pl
# Authors:  Arnab Saha-Mandal & Alexei Fedorov
#           Bioinformatics Lab, The University of Toledo Health Science Campus
#           Ohio, USA
# January, 2013
# Contact arnab.sahamandal@rockets.utoledo.edu OR alexei.fedorov@utoledo.edu
# license under GPL version 2 or later
# If you use this code or incorporate it in another program please cite our paper "Saha-Mandal et.al", 2013.
# This Perl script does the following:

# In case the number of simulations are of the order of several millions or higher,
# The program should run in background and output directed towards a file
open (OUT, ">monte_carlo_output");

#initializing user inputs from keyboard
print "Please enter the number of heads\n";
$v1 = <STDIN>;
print "Please enter the number of tails\n";
$v2 = <STDIN>;
print "For how many simulations do you want to run?\n";
$s = <STDIN>;

#putting the count to zero and looping the process over desired number of iterations
$count = 0;
for $x(1..$s){
        $head=$tail=0; #variables for counting heads and tails initially set to zero

        #sublooping within a particular iteration for total number of coin tosses in an event
        for $n(1..($v1+$v2)){

                #choosing a random number between 0 and 1 and counting outcomes within the event
                $r = int(rand(2));
                if ($r == 1){
                        $head++;
                }
                else {
                        $tail++;
                }
        } #closing the subloop

        #computing difference within the outcomes
        $d = abs($head - $tail);
        if ( $d >= abs($v2-$v1)){
                $count++;   #incrementing the count in case a difference greater than
                            #expected is observed
        }
} #closing the major loop after all the iterations have been completed

#calculating the probability of fluctuation due to all the number of
#iterations and thereby printing it onto the screen or using
#"print OUT"(see beginning of code) if printing to a file

$h = $count/$s;
print "P-value = $h\n";