Author: Robert Hyatt
Date: 12:50:04 01/20/01
Go up one level in this thread
On January 20, 2001 at 14:20:56, Ricardo Gibert wrote: >On January 20, 2001 at 10:48:59, Robert Hyatt wrote: > >>On January 20, 2001 at 05:29:23, Ricardo Gibert wrote: >> >>>On January 20, 2001 at 00:17:26, Robert Hyatt wrote: >>> >>>>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 >>> >>>But Whites King is not too far away! It is obstructed by the e-pawn. Without the >>>e-pawn, the King is just in time. White loses due to the connected passed pawns >>>*plus* obstruction of its King. Unless your eval handles connected passed *and* >>>obstruction correctly, Crafty must solve it by searching a bit deeper. If it is >>>not doing that, it is guessing. >>> >> >>Unless I have broken something without knowing, it doesn't "guess". It simply >>asks "can the king reach the queening squares in time. And it uses some bitmap >>trickery to answer this, which also happens to detect the interference caused >>by its own pawn. > >Even if it does detect the "interference" of the e-pawn, your program must still >search, since in a similar position, the e-pawn might be able to move out of the >way with check and allow the White King to defend in time. That is why this is done at _endpoints_ after a decent search, rather than in lieu of a search. The search is supposed to clear up the tactics so that the eval can accurately decide who is winning... > >> >>I simply ask "how many moves to reach square X"? I'll look to be sure that >>has not been broken somehow... >> >> >> >> >>>>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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