Author: Robert Hyatt
Date: 17:51:38 08/13/00
Go up one level in this thread
On August 13, 2000 at 18:47:42, Alvaro Rodriguez wrote: >On August 13, 2000 at 18:20:33, Robert Hyatt wrote: > >>On August 13, 2000 at 16:21:34, Uri Blass wrote: >> >>>On August 13, 2000 at 15:12:25, Christophe Theron wrote: >>> >>>>On August 13, 2000 at 11:42:57, Mike S. wrote: >>>> >>>>>On August 13, 2000 at 10:59:22, pete wrote: >>>>> >>>>>>(...) >>>>>>[D]3r1rk1/2p1Rppp/p4n2/1p1b4/3P4/3B3P/PPPN2P1/4R1K1 b - - 0 1 >>>>> >>>>>It seems to me that Tiger, when playing 21...Bxa2?, cannot have expected 22.b3. >>>>>Maybe he expected something like 22.Rxc7 Rxd4 23.Ra1 Bd5 24.Rxa6 or similar. I >>>>>would be interested if Tiger "knows" this standard motif of locking up a bishop >>>>>after it captured a border pawn on the 2nd (7th) row. I think, in such cases the >>>>>lines beginnig with b3 etc. should be examined more closely than usual (?). >>>>> >>>>>Regards, >>>>>M.Scheidl >>>> >>>> >>>> >>>>Chess Tiger 12.0e has a partial knowledge of this "standard motif". It knows >>>>that the bishop is in trouble if it cannot leave a2, but the evaluation penalty >>>>I give in this case does not prevent it to take the pawn. >>>> >>>>That means that if another move could lead to a positional advantage, Tiger >>>>would play the other move. If there is no such move, Tiger will take the pawn >>>>with the bishop. >>>> >>>>I know it sounds a little bit strange, but I have been thinking about this >>>>problem for quite a while, and I have not found a good solution. For every >>>>example of a trapped bishop that gets lost I have seen the opposite example >>>>where the trapped bishop eventually escapes or completely shreds the side it has >>>>been trapped in, which leads to a big pawn majority and a winning endgame. >>> >>>The question is what happens in cases when you cannot find by a search of few >>>minutes that the bishop can escape and cannot find by a search of few minutes >>>that the bishop is trapped. >>> >>>I believe that in most of these cases moves like Bxa2 are wrong but I may be >>>wrong because I did not see a lot of examples when search cannot solve the >>>problem. >>> >>>Uri >> >> >>I prefer to be conservative here. Rather than trying (a) if the bishop isn't >>lost, then take the pawn, I prefer (b) if the bishop can't get off of a2 by >>the time the evaluation is called, then it is trapped. >> >>Works well for me, very inexpensive to test for. > >Crafty takes the pawn if the analysis shows that it can get out? So crafty takes >no risk.. Interesting to see what the other program does in this positions.. > >Regards, >Alvaro That is correct. It has to see taking the pawn, _and_ the bishop getting off of a2, within the search. Otherwise it assumes that the bishop is trapped and gives it a huge penalty. I haven't seen it fail very often, and when it did fail, the position was complex enough that it wasn't possible to understand it with a simple static eval trick anyway. The amazing thing is that I _still_ see it happening on ICC... I got tired of seeing crafty do that pretty quickly. I decided that sitting in a game and worrying about whether it will play a move that even a 1600 player would avoid was simply something I didn't want to do. As a result, I don't. :) A 2500 (GM-level) program simply can _not_ play such a move. If it does, and a GM sees it, it will lose the next N games because he will set that trap over and over... and the program will bite over and over.
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