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Re: MML dispatch
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From:
Nicholas Clark
Date:
August 15, 2005 12:18
Subject:
Re: MML dispatch
On Wed, Jul 13, 2005 at 06:07:55PM +1000, Damian Conway wrote:
> The use of summed lineal distance (L[1]) rather than RMS distance (L[2])
> 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[1] versus L[2], 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
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