#!/usr/local/bin/perl

# ----------------------------------------------------------------
# John Kerl
# kerl.john.r@gmail.com
# 2005-01-11
#
# This is an example of numerical integration in one variable:
# sin(x)/x from -2 pi to 2 pi.  A reference value for the integral is
# 2.83630; this program prints 2.836350.
# ----------------------------------------------------------------

$pi  =  4.0 * atan2(1,1);
$xlo = -2.0 * $pi;
$xhi =  2.0 * $pi;

$nx  = 400;
$nx  = $ARGV[0] if (@ARGV);
$dx  = ($xhi - $xlo) / $nx;

# Alternatively:
#$dx  = 0.001;

$sum = 0.0;
for ($x = $xlo; $x < $xhi; $x += $dx) {
	$y = f($x);
	$sum += $y * $dx;
}
printf "%11.6f\n", $sum;

# ----------------------------------------------------------------
sub f {
	my ($x) = @_;
	if ($x == 0.0) {
		return 1.0;
	}
	else {
		return sin($x) / $x;
	}
}