Author: Uri Blass
Date: 03:14:32 08/24/04
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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. > >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). > >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). > >Tord The idea is simple but the problem is to write evaluation to evaluate the variety of the score. evaluating probabilities(loss draw win) so you can calculate the variaty is the best thing to do but I do not know of a single program that work in that way. Uri
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