Author: Robert Hyatt
Date: 18:02:36 01/19/01
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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 The problem is the checks by the white rook _after_ you play Rxb2 and white takes back. Those checks delay this for a while. I think it takes crafty 12 plies to solve this tactically (it solves it almost instantly because it has an eval term for two connected passers on the 6th (or furthar advanced) with certain constraints on the enemy king, etc.) You are probably doing just fine...
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