Author: Bas Hamstra
Date: 21:35:05 01/20/01
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On January 19, 2001 at 19:44:49, Vincent Diepeveen wrote: >On January 19, 2001 at 17:23:03, Scott Gasch wrote: > >>Hi all, >> >>Here's a pretty simple test position. This comes from the WAC suite... my >>engine does fairly well on this suite as a whole but seems blind to this >>solution. >> >>[D]8/7p/5k2/5p2/p1p2P2/Pr1pPK2/1P1R3P/8 b - - >> >>The solution is Rxb2 -- black's connected passers are unstoppable after the >>recapture. >> >>My program refuses to find this solution... even at 9 ply it misses it. The >>strange thing is that from the other side after Rxb2 it sees that white is toast >>very quickly... score dropping to -500 or so after about 1 second. >> >>My question is, of course, how this move is missed. I've tried kicking up the >>value of connected passers and passed pawns in general. I've tried adding a >>special rule to eval about connected passers on the 7th, on move, with control >>of a queening square. I've tried cutting back my futility margin in qsearch and >>always extending a full ply for checks (It usually extends only 3/4 ply for >>checks after the iteration depth). And still it does not find Rxb2. >> >>Even stranger is if I run a static eval with the two connected passers rolling >>towards the queening square after the rook exchange the eval puts black ahead! >>I can't seem to figure this out... either my pruning is too aggressive or there >>is some other bug in the engine...? >> >>I hope someone out there can give me a little advice. Thanks! >> >>Scott > >First of all this combination is not 9 ply but something >like 14 ply. Most programs solve it incorrectly at small depths as >they don't evaluate kings stopping passers or because they just >give huge scores for doubled passers. > >Secondly important is to do promotions in qsearch for this >position. Do you? > >If you do then with that check extension added it should be 14 ply >this combination. I can confirm this. If you evaluate pawns on the seventh adequately it is 12 ply. With some 2-pawn sixth eval you will see it instantly. It takes 14 ply to see the actual queen. Bas.
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