use strict;
package ComplexCalculation;
sub do_calc {
  # put your calculation here.
  return 4 + 8 * 15 / 16 - 23 * 42;
}
1;

##</code><code>##

$variable1 = ComplexCalculation::do_calc();

##</code><code>##

use ComplexCalculation;

##</code><code>##

use lib '/some/path/to/the/calc/module';

##</code><code>##

sub do_calc {
  my $v1 = ##... something
  my $v2 = ##... other thing
  my $v3 = ##... a third thing
  return $v1, $v2, $v3
}

##</code><code>##

my ($r1, $r2, $r3) = ComplexCalculation::do_calc()

##</code><code>##

my ($weight, undef, $depth) = ComplexCalculation::do_calc()