Author: Anthony Cozzie
Date: 08:29:31 08/24/04
Go up one level in this thread
On August 24, 2004 at 10:37:02, Vasik Rajlich wrote:
>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
>
>You're (probably) right that these are good positions in which to extend, but
>IMO the justification should be put differently.
>
>There should be a 1-to-1 mapping between the output of your static eval and
>winning %. (As I am sure you agree.) If you're uncertain - it just means that
>the score needs to be brought closer to 0. So, having eval return {eval,
>uncertainty} is redundant. However, what eval can return is {eval,
>"likelyhood-that-one-extra-ply-of-search-will-change-the-eval"}. This second
>term should be higher when the king is exposed, or when there are passed pawns,
>and it should be the justification for this sort of extending.
>
>Hope this is useful (rather than a nitpick) ..
>
>Vas
I think Tord's point is that big kingsafety scores are _always_ inaccurate ;)
anthony
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