Author: Richard Pijl
Date: 05:56:14 12/15/05
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On December 15, 2005 at 05:59:21, Gerd Isenberg wrote: >Hi, > >recently there was the question about a knight-distance formula. >Mungjong pointed out the idea with the 0x88 square difference and a lookup, >while Uri mentioned the edge-cases which require some special handling. > >I still have my precalculated 64*64 array with packed distance, taxi-distance, >knight-distance and this udr-value (unique distance relation). > I'm not sure what you can do with the knight-distance. The obvious case (to check whether a passed pawn can be stopped by the knight) is obviously not very useful, as there are plenty of cases where the knight (by means of an intermediate check) can 'win' a move. Besides, in most cases the 'stopping' capability of the knight is more restricted by pawn and king positions than anything else anyway. finally, you should also consider alternative stopping fields like the second rank, as sometimes it is possible to reach a stopping field other than the promotion square. You'll have to get there faster then, of course. I have tried using this, but without useful results. It is possible to do this kind of analysis though, but IMHO a different approach is needed where pawn structures and possibilities of intermediate checks are taken into account. Ofcourse, this will not be a cheap check. I've done something like this in the Baron (since version 1.6.1) which seems to work ok in quite a few cases. Although it still doesn't detect unstoppables in many cases, I don't think it gives much false positives either (which would be much worse of course). consider the following examples (recognized correctly in evaluation, so without search): [D]8/3k1p1N/5P1p/8/1p6/8/7K/8 w - - Pawn is unstoppable [D]8/3k3N/7p/8/8/1p6/7K/8 w - - Pawn is not unstoppable, due to check on f6 [D]8/3k1p1N/5P2/8/8/1p6/7K/8 w - - Pawn is unstoppable, check on f6 is not possible Richard.
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