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Subject: Re: not using nullmove?

Author: Dann Corbit

Date: 18:00:08 02/17/04

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On February 17, 2004 at 20:55:13, Dann Corbit wrote:

>On February 17, 2004 at 12:03:03, Tord Romstad wrote:
>>On February 17, 2004 at 08:19:28, martin fierz wrote:
>>>On February 17, 2004 at 07:55:32, Tord Romstad wrote:
>>>>KR vs KP is a difficult one.  Does anybody have any good suggestions about
>>>>how to evaluate it?  At the moment I don't have any specific code for this
>>>>endgame at all, and Gothmog almost always evaluates it as a win for the rook.
>>>>In reality, it is of course very often a draw.
>>>i'll have to think about this one too. i haven't done either KR-KP or KQ-KP;
>>>KQ-KP should be rather easy as there are basically only two drawing positions;
>>Yes.  KQ-KP is much easier, and also less important, because the probability
>>of a draw is much smaller here.
>>>KR-KP is much harder. but you should at least be able to easily identify many
>>>cases where KR is clearly winning; e.g. any time the KR-side king is in the
>>>square of the pawn KR is winning (with one exception: wKe2, bPd2, bKf1/f2, black
>>>to move, but qsearch should catch that).
>>This is a good start, but I think it might be more valuable to work
>>from the other end:  Which positions do we know are drawn?  I guess
>>the probability of a draw is big if the pawn is on the fifth rank or
>>beyond and supported by the king, and the attacking king is far away.
>>But this is certainly too simple to be a sure drawing rule.
>>There is also not many clear rules to be found in Keres' "Practical
>>Chess Endings" (my main endgame reference), which makes me fear that
>>it is not easy to evaluate this endgame correctly.
>Here's a dumb idea:
>Write a program to scan a Nalimov database, but throw away everything except
>won/lost/drawn/broken (needs 2 bits per reflected board position to store the
>outcome state).
>Then write a table.
>For up to the 4 man tables, it should be really tiny and fit into ram without
>any fuss.
>Seems like one single program could write a recognizer for anything [for which a
>Nalimov or Edwards or Thompson EGTB exists].

One step further:
For the list of possible board positions for a given class (e.g. KRK) create a
list of them.  Then create a perfect hash for these positions.

Then, in your program, the table holds:
HASHVAL, won/lost/drawn/brokenbits

If (for instance) there were 65,000 possible postions after all reflections and
rotations, then you would only need 18 bits per position to store the hash and
the answer.

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