Author: Robert Hyatt
Date: 07:54:40 08/24/04
Go up one level in this thread
On August 24, 2004 at 04:57:02, Tord Romstad wrote: >On August 23, 2004 at 23:04:13, Robert Hyatt wrote: > >>This particular case is not a big issue with me. I personally believe that the >>+2 eval is wrong. And it would be interesting to keep the same position, but >>move a white piece or pawn and see what happens and if black would still play >>the same. IE maybe white bishop at d1 rather than a1. That changes the >>position although I have not given a lot of thought to this... > >I think this particular case *should* be a big issue to you, and I'll try >to explain why. The kind of position we have after 1... Nxh3 2. Kxh3 >Rh6+ 3. Kg4 is extremely hard to evaluate accurately. It is very possible >that your statement that +2 for black is wrong. Clearly, it is very risky >to evaluate such positions as winning for black, and doing so will sometimes >cause your engine to lose games. On the other hand, it is just as risky >to evaluate the position as winning for white. With the white king so >exposed and no easy way home, it is very possible that black has a >winning attack. Note that I _don't_ evaluate it as "winning for white". Crafty says "draw" as do most other programs. I don't want to have a +1.6 position, and play Nxh3 to reach what I think is a +1.8 position, only to see it fade to +0 and a draw. If Crafty said +2 for white and Pro Deo +2 for black, I would be worried. It may well be that it does win for black with very accurate play, which means that it is ok Here. But if it is possible to change the location of one white piece to prevent the loss, and black still goes for this, you just gave humans a big hole to walk through repeatedly... > >Not only is the position very difficult to evaluate, it is also a very >important position. The line is almost forced, and the likelihood that >the resulting position is won for one of the players is very high. > >The best way I have found to handle such positions is to extend. When >one side has a winning material advantage, but the other side has a >very dangerous attack, extend by half a ply or so. This will often >help you to discover and correctly evaluate sacrifical kingside attacks >several plies earlier, and the cost is very low in most positions >(because such attacks are rather rare). I don't disagree. Search over Eval is more accurate in most cases. Of course you can't always search deeply enough and will have to rely on evaluation in many positions. :) > >Making the static eval aware of its limitations offers many interesting >possibilities, and I think there are many valuable and important ideas >waiting to be found by the adventurous programmer here. The basic >idea is to extend in positions where the static eval is likely to be >highly inaccurate, and to reduce in positions where it is likely to >be very accurate (internal node recognizers is an extreme special case). > That is exactly the "definition" of "quiescence search". To search until you reach positions your evaluation can handle accurately. :) Hence all the various kinds of search extensions we use also... >Tord
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.