#!/usr/bin/perl 
use strict;
use warnings;
use Time::HiRes qw( clock );
# NOTE, the HiRes.pm is automatically there in Linux
# but not on the MAC. I could not easily recompile
# the Linux version to run on the MAC.
#
my $clock0 = clock(); # Start clock to monitor CPU time
# Start of monitoring for time.
# Script created for calculating Pi
# Uses the Gregory-Leibniz Series
# Found on http://en.wikipedia.org/wiki/Pi#Calculating_.CF.80
#
# Author: Mark Stump, Amended by Victor Odlivak July 27, 2007
#
# input:  an integer stating number of iterations desired for
# converging PI series from Leibniz etc.
#
# PI = 4 +4/3 -4/5 +4/7 etc.
#
# output:  Approximation for PI to desired number of iterations of
# series. 
#
#  usage   perlpi i 
#  where   i is an integer between 1 and 10000000.
# 
sub calc_pi {
my ($numIterations)  = @_ ;# number of iterations of loop to
# calculate PI. 
my $numerator = 4;
my $denominator = 1;
my $negVal = 1;
my $calculatedVal = 0;
my $j = 0;
# Number of iterations for loop to calculate pi
for  ($j = 0; $j < $numIterations; $j++) {
$calculatedVal += $negVal * ($numerator/$denominator);
# Note, numberator is always four. It does not change.
$negVal *= -1; #reverse the sign for each iteration telling
# whether to add or subtract.
$denominator +=2; # The denominator is always two more, than it
# was in the term before.
}
return $calculatedVal;
}

# Main Program Section

 my $num_cycles = shift(@ARGV);
 unless($num_cycles) {
 print " Sorry, you forgot to enter an iteration number for the ";
 print " PI series.   \n\n usage:  perlpi i \n\n"; 
 print " where i is an integer between 1 and 100,000,000\n\n";
 exit;
 }
my $approx_pi = 0;

print "Starting CPU timer at $clock0 seconds .. be patient please if";
print " you are doing over a million iterations \n";
$approx_pi = calc_pi ($num_cycles);
print "The calculated value of pi with $num_cycles";
print " cycles of the calculation loop is: \n";
print " $approx_pi \n";
my $clock1 = clock();
my $clockd = $clock1 - $clock0;
print "Finishing time is = $clockd seconds \n";