#!/usr/bin/perl
#
# This script calculates the scattering time using
# the empirical relationship between scattering time, DM and
# observing frequency (Bhat et al., 2004)
# 
# (c) Vlad Kondratiev, 2007
#
if ($#ARGV < 1) {
 print "Usage: $0 <DM> <Freq>\n";
 print "  DM   - in pc/cm^3\n";
 print "  Freq - in GHz\n";
 print "The program gives a value of scattering time (in mcs)\n";
 print "It is based on the empirical relationship from Bhat et al. (2004)\n";
 exit 0;
}
$dm = $ARGV[0];
$freq = $ARGV[1];
$logtau = -6.46 + 0.154*&log10($dm) + 1.07*&log10($dm)*&log10($dm) - 3.86*&log10($freq);
$scat = &power (10., $logtau);
printf ("Scattering time = %.3f mcs\n", 1000.*$scat);


# Subroutine to calculate 10-base logarithm
sub log10 {
 my ($val) = @_;
 return log($val)/log(10.);
}

# Subroutine to calculate x^y
sub power {
 my ($x, $y) = @_;
 return exp($y * log($x));
}