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Subject: Re: Draw due to lack of blockade detection...

Author: Sune Fischer

Date: 11:53:09 10/04/02

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On October 04, 2002 at 14:31:16, Vincent Diepeveen wrote:

>On October 04, 2002 at 12:28:54, Sune Fischer wrote:
>
>>On October 04, 2002 at 12:14:18, Omid David wrote:
>>>>>Wrong. I've conducted hundreds of tests, and in no single case has my heuristic
>>>>>returned an inaccurate result. There exist blockades that it fails to detect,
>>>>>but it never declares a false draw.
>>>>
>>>>Perhaps this is too restrictive too.
>>>>You could have some confidence variable, if you draw detector cannot say with
>>>>100% certainty that it's draw, then interpolate the evaluated score with the
>>>>confidence level: score=eval()*(100-confidence)/100.
>>>>
>>>>It might help the engine to steer clear of those drawish positions?
>>>
>>>But as Vincent pointed out, such heuristics have an overriding nature. Even the
>>>slightest inaccuracies can result in a total disaster.
>>
>>Yes I know, you have to be careful, right now I don't even score KRKR as draw,
>>because what if the one to move can give a check and take the other rook hiding
>>behind the king...
>>
>>If there is a high probability of a draw, eg. a risk of perpetual check because
>>your king is exposed and his queen is near by, then be less optimistic in your
>>score even if you are way ahead in material. It is probably easier to win
>>without the queens on the board if you have an extra knight, for instance. At
>>least you have eliminated the risk of perpetual check.
>
>One of the things we are talking about here is that black is a pawn
>down. Not about KR KR or something.

Yes, I know that, it was just an example of why it is dangerous to score
accurate, as you said yourself.

>KR KR is not a 'blocked position'. He talks about recognizing something
>as blocked and therefore giving a pawn up. In that 'easy' to recognize
>draw from kramnik you put the black king on a7 and dang it's a zero.
>
>see my position example elsewhere. So your engine exchanges to a position
>with pawn down to reach somewhere in far horizon a draw score from eval.

I saw your position, and you are assuming his detector ignores the position of
the kings. Had the king been within the square it would have been draw, right?

>then when you get near that position it is simply a pawn down as it sees
>that position is tactical lost completely. This happens to be a lot of times
>the case in blocked positions.

What I was suggesting was to use a confidence score, in your position it would
evaluate (staticly) white as +1 up, then it would say "but there is a 30% chance
of a draw for black because of a lot of blocked pawns", the score would then be
+1*(1-0.3)=+0.7 and not 1.0.
So black wouldn't sac a pawn here because +0.7 is still worse for black than
0.0, which might have been the material score had it not sacrificed a pawn.

I don't see anything wrong with this, as long as your draw detector is
reasonably accurate of course. The idea is the program might choose a different
more secure way to the win, rather than entering a type of position where the
opponent has a lot of drawing chances.
I would like to get this "there is a danger of draws here, so pick a different
variation if possible" knowledge into my program.

>GMs are world champion winning blocked positions, let me tell you that...
>...blocked positions that Omar scores of course each time as a draw :)

Yes, which is why it is all the more important to remove this human advantage :)

-S.



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