Author: Christophe Theron
Date: 14:52:40 07/21/99
Go up one level in this thread
On July 21, 1999 at 01:33:46, Paulo Soares wrote:
>On July 21, 1999 at 00:56:56, Christophe Theron wrote:
>
>(snip)
>>
>>Some programs don't see the mate in 2 (with both pawns on the 7th rank) because
>>after 1. Ra6! black is in zugzwang.
>>
>>Looks like nobody has read my previous post and I'm just losing my time trying
>>to explain it...
>>
>>Both Hiarcs and Fritz would fail on some zugzwang positions. Not on this one,
>>which is solved by Hiarcs, but there are positions where Hiarcs fails completely
>>because of its null move algorithm.
>>
>>...OK, just losing my time... :)
>>
>>
>> Christophe
>
>Christophe, this question was made by Eric Guttemberg, and was without
>reply. Could you answer, I have the same doubts of Eric.
>
>"With regard to the zugzwang problem, I am a little confused. I know that
>many basic endgames techniques rely repeatedly on the zugzwang theme. In
>many of them the weaker side would never lose if he could waive his move
>when it suited him(mating with K and R vs K is a whole different ballgame
>if the weaker side can not be forced to move)
>Yet Fritz does not seem to have any trouble with any of the basic endgame
>positions. What kinds of zugzwang positions does Fritz and other null-movers
>have trouble with?"
>
>Paulo Soares, from Brazil
I don't know exactly which kind of positions Fritz will have trouble with. But
every programmer that uses null move knows about the "overlooking zugzwang"
disaster.
So they try to avoid it by disabling the null move algorithm in positions where
a zugzwang is likely. Obviously, in endgame positions.
They set some kind of material thresold, and if the current material on the
board is under this thresold, the null move selectivity is simply disabled.
This can even be smarter. For example, it is unlikely that a side will be in
zugzwang if he has a queen. It is also unlikely that it will happen if a side
has more than 2 pieces (excluding pawns and king), though it is more risky to
assume this. Needless to say, you can find positions where one side, even with a
queen and another piece, is in zugzwang. But it is very very rare.
Such a position has been posted recently, and guess what... Hiarcs fails to
solve it for example (I'm almost sure Fritz would fail too).
Apparently, Fritz makes very risky assumptions about this, and gets caught more
often than other programs. To be honest, it is not a big problem in the real
games. The only danger, and I suppose Frans Morsch doesn't care too much about
it, is that you'll always find somebody laughing at you because you failed on a
study...
Christophe
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