my @vector1 = ( 2, -4, 2 );
my @vector2 = ( 5, -3, -6);

##</code><code>##

      return unless $ct1 && $ct1 == $ct2 && $ct2 == $ct3;

##</code><code>##

      my $sum = 0;
      foreach my $i ( 0 .. $#$x ){
        $sum += $x->[$i] * $y->[$i] * $z->[$i];
      }
      return $sum;

##</code><code>##

  my $sum = 0;
  $sum += $x->[$_] * $y->[$_] * $z->[$_] for 0 .. $#$x;
  return $sum;