use strict;
use warnings;

my $ret = vector_sum(
        [ 3, 9, 24, 31 ],
        [ 9, 5, 11, 25 ]
   );

print join(", ", @{$ret}), "\n";


sub vector_sum
  {
  my ($v1_ref, $v2_ref) = @_;
  my $ret;

  return undef if (scalar(@{$v1_ref}) != scalar(@{$v2_ref}));
  for my $i (0 .. scalar(@{$v1_ref})-1)
    {
    push @{$ret}, ($v1_ref->[$i] + $v2_ref->[$i]);
    }

  return $ret;
  }