Integral equation using PerlGSL

perlgsl.pl

#!/usr/bin/env perl

use strict;
use warnings;

use PerlGSL qw/int_1d findroot_1d/;

#  _             2           
# /  1          x            
# |    exp(  -  -- ) dx  =  c
#_/  0           2           
#               a            

# solve for 'a' for a given 'c'

my $c = 0.5;
my $eqn = sub {
  my $a = shift;
  my $integrand = sub {
    my $x = shift;
    return exp( - $x**2 / $a**2 );
  };
  return int_1d( $integrand, 0, 1 ) - $c;
};
my $found = findroot_1d( $eqn, 0.1, 10);

print $found . "\n";