Author: Christophe Theron
Date: 10:55:58 11/23/01
Go up one level in this thread
On November 23, 2001 at 06:51:46, Colin Frayn wrote:
>On November 22, 2001 at 22:22:13, Christophe Theron wrote:
>
>
>[D]8/1KPk4/8/6p1/p7/8/8/8 b - -
>
>>A simple definition of "quiet" is that a position is not quiet if one side is in
>>check, one side has a winning capture, or one side can promote.
>
>Well, firstly, it's black to move. Secondly, one could easily retract the last
>couple of moves, getting to this position,
>
>[D]8/8/1KPk4/6p1/p7/8/8/8 w - -
>
>... which is also obviously won for white, but which nobody spots statically.
>You're now quite a few ply away from the winning promotion. Fortunately I
>changed Beowulf's eval() so that it now spots similar positions to these quite
>easily. The reason why programs don't understand them is the following; (and
>Crafty scores this as something like +7.5 pawns for black)
>
>Black has two totally passed pawns (safe from opponent king, no opposing pieces)
>which are scored extremely highly. White has one passed pawn, but it is not
>even safe from the black king. Well... in fact it *is* because it can be shown
>that white will always be able to promote this type of passed pawn (assuming no
>other opposition) because his own king is defending. Anyway, I only conssider
>pawn races for totally passed pawns, so the first important change is to
>recognise that this white pawn is in fact totally passed.
>
>Secondly - the fact that white will promote first effectively means that black's
>two passed pawns are useless - there's no point giving them the extra bonus for
>being totally passed as soon they won't be - i.e. there will soon be an opposing
>queen to deal with, and they'll both be captured. If we don't give them huge
>bonuses (in Beowulf, that bonus is 4 pawns worth) then the situation is scored
>as a strong win for white.
>
>I keep finding these types of problems. And no, the answer isn;t to use
>tablebases, as it's reasonably easy to construct a situation with a few extra
>pawns in where the same rule applies.
>
>Cheers,
>Col
Chess Tiger 14.7 evaluates statically this position (no search) as +0.62 for
white.
So it does not evaluate it as a clear win for white, but at least it knows that
white is better.
Christophe
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