Author: Robert Hyatt
Date: 21:10:22 08/13/00
Go up one level in this thread
On August 13, 2000 at 23:41:03, Uri Blass wrote: >On August 13, 2000 at 20:51:38, Robert Hyatt wrote: > >>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. > >I disagree. > >I do not think it is so easy to set the trap again and again. >Remember that you have to set it in positions that the program cannot detect the >loss of the bishop by search. A GM/IM can do this pretty easily in half of the games. why do you think I fixed it? one particular IM was very good at setting this up, over and over and over.. > >I guess that your opinion is based on your experience on ICC but the hardware >today is faster and programs can see more things by search. > >Uri Most of those positions can not be solved by search. All it takes is for black to have a missing a pawn, and black's rook holds the bishop for a long time. But with the bishop stuck at a2, all of black's energy goes into trying to extricate the bishop. All of white's energy goes into trying to snare black's king. White succeeds more than black.
This page took 0 seconds to execute
Last modified: Thu, 15 Apr 21 08:11:13 -0700
Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.