Author: Robert Hyatt
Date: 21:17:26 01/19/01
Go up one level in this thread
On January 19, 2001 at 21:51:09, Uri Blass wrote: >On January 19, 2001 at 21:33:08, John Merlino 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 >> >>Just to make things difficult, Chessmaster 8000 seems to have this one's number, >>AND it reports the correct move at ply 9, despite other postings here that have >>stated that it should take somewhere between 12 and 14 plies to find the result. > >You are right and it is also clear from the main line that it can see the queen >on the board and does not solve it for wrong positional reasons that vincent >suggests. > >Uri I would disagree with Vincent's reasoning. Crafty solves it for the _right_ positional reasons before it sees the tactical win. It notes that the king can't stop the pawns, and it _knows_ that a rook can't stop them. Hence this is the _right_ reason here... even without seeing deep enough to see the actual promotion. It only takes crafty a few seconds to see the actual promotion so it is really moot... but to say that at 8 plies it solves it for the wrong reasons is a stretch at least. ie if you have a rook, I have two connected passers on the 7th, and your king is too far away to help, I am going to get a queen and there is nothing you can do about it. Whether my eval recognizes that, or I have to wait for the search to recognize it doesn't matter. the pawns are going to win...
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