I didn't know about "can" - that's pretty neat. But I'd really like to make a reference I can store, since I'll be calling the "method" function throughout the program; what I have in the meantime looks like this:

sub w
{
  my($self, $a, $i) = @_;

  if($self->{method} eq 'correlation') {
    return $self->correlation($a, $i); }   
  if($self->{method} eq 'vector_similarity') {
    return $self->vector_similarity($a, $i); }
  if($self->{method} eq 'IUF') {
    return $self->IUF($a, $i); }
  if($self->{method} eq 'MSD') {
    return $self->MSD($a, $i); }
}
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The w function gets called quite a few times, so I don't want a per-call check.

Thanks for the tip on constructors; that's a good point.

dan