On Wed, Jul 13, 2005 at 06:07:55PM +1000, Damian Conway wrote: > The use of summed lineal distance (L) rather than RMS distance (L) > probably *isn't* superior as a closeness measure. But it's computationally > much simpler (and hence likely to be more efficient), it doesn't suffer > from precision issues in "photo finishes", and it is almost certainly > easier for the average programmer to predict correctly.
I dispute "much", specifically because the sum of the squares has the same ordering as the square root of the sum of the squares. (So we're talking only about 1 extra multiply per class under consideration, and a possible overflow or need for floating point, rather than the more direct assumption that ordering by RMS would need a square root evaluated) But I have no opinion on the underlying merits of L versus L, because I have no experience of MMD. > That said, I'd have no *particular* objection to an MMD implementation that > used RMS inheritance distance as its metric, provided the dispatch > performance was not appreciably worse. Maybe I should cut that paragraph, to avoid re-opening a debate. Nicholas Clark