Author: Vasik Rajlich
Date: 10:24:03 08/24/04
Go up one level in this thread
On August 24, 2004 at 11:29:31, Anthony Cozzie wrote:
>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
If that's the case, then evals for positions with big kingside scores should
always be adjusted in the direction of 0.
Some time ago I considered returning an evaluation uncertainty from my eval. I
decided that no such thing existed - it's an inherent part of the eval score.
Vas
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