use strict;
use warnings;

my ($i);				#declare global $i for for loop
my (@sigmas, @rads);	#declare arrays for storage of radii and sigma results

for ($i=1;$i<=100;$i+=2) {	# 1, 3, 5, ..., 99
	my $r = ($i)*(1e-6);	#radii are in microns
	push (@rads, $r);		#store the correct radii in array for print at end
	
	if ($r<2e-5) {					#if the radius is <20microns, send to sub sigmalow
		my $sig = sigmalow($r);		#store the return in $sig
		push (@sigmas, $sig);		#add result to the final sigma array
		}
	else {							#if the radius is >=20microns, send to sub sigmahigh
		my $sig = sigmahigh($r);	#store the return in $sig
		push (@sigmas, $sig);		#add result to the final sigma array
		}
	}

print "radii: @rads \n";	
print "sigmas: @sigmas \n";


exit;

sub sigmalow {	#to compute sigma when radius < 20microns
	
my ($pi, $a, $c, $rad, $sig);
my (@r);

$pi = 3.14159;		#constants
$a = 1.18;
$c = .28e6;
	
@r = @_;		#transfer the argument to @r
$rad = $r[0];	#is this step necessary?
$sig = $pi*($rad**2)*$a*(1-exp(-$c*$rad));	#calculation of sigma

return ($sig);	#send back the result

}

sub sigmahigh {	#to compute sigma when radius >= 20microns
	
my ($pi, $rad, $sig);
my (@r);

$pi = 3.14159;	#constant

@r = @_;		#transfer the argument
$rad = $r[0];	#necessary?
$sig = 2*$pi*($rad**2);	#compute

return ($sig);	#return it

}