Author: Albert Silver
Date: 19:56:50 05/24/00
Go up one level in this thread
On May 24, 2000 at 22:26:31, Roberto Waldteufel wrote:
>On May 24, 2000 at 20:00:53, Robert Hyatt wrote:
>
>>On May 24, 2000 at 19:51:35, Roberto Waldteufel wrote:
>>
>>>I have noticed a weakness in my program in situations where there are advanced
>>>passed pawns, but often the promotion is not seen before it is already too late
>>>to stop, or else can only be stopped by sacrifice of material. Usually the
>>>program has missed a chance to stop the pawn much more cheaply, being distracted
>>>by some small material gain on the other side of the board, or else pushing the
>>>promotion beyond the search horizon by means of a series of checks from which
>>>the oponent can ultimately escape safely. Does anyone extend their searches for
>>>passed pawn pushes? If so, how is the extension triggered - does it depend on
>>>the rank of the pawn, the king position, and/or the currant remaining search
>>>depth? At present I consider pawn promotions in the qsearch (depth<=0) and I
>>>extend 1 ply for pawn pushes to the seventh rank at frontier nodes (depth=1),
>>>so the oponent cannot stand pat without giving the pawn a chance to promote, but
>>>I do no other pawn-triggered extensions at all. I think that pushes to the
>>>sixth rank probably should be extended as well, but to ensure that promotion
>>>occurs before standing pat this would need a lot of extra full-width plies. Any
>>>suggestions?
>>>
>>>Best wishes,
>>>
>>>Roberto
>>
>>
>>Make the value of a passed pawn larger. And make this value proportional to
>>the number of squares it has advanced. Then you will try to restrain/blockade
>>the pawn based on positional grounds.
>
>I already apply a bonus in the evaluation for passed pawns which increases as
>the pawns advance, and is smaller if the pawn is blockaded. Most of the time
>this works quite satisfactorily; the trouble arises when this bonus is exceeded
>by a material gain, say of a pawn or two, which causes the program to gobble the
>pawns and then push the promotion beyond the horizon with forcing moves,
>typically checks or long swap sequences. I could make the passed pawn bonus
>bigger, but this would cause problems with lazy evaluations, as my total
>positional score is never worth more than 2 pawns, so I make use of lazy
>evaluation to speed things up when the material score is more than 2 pawns below
>alpha or above beta. This means that if the program reaches the qsearch and is 2
>pawns or more outside the search window on material it does not even bother to
>test for passed pawns - maybe it should test anyway, but that increases the
>qsearch workload quite a lot. How big is your passed pawn bonus relative to to
>material value? I might have to increase my tolerance to 3 pawns instead of two
>and increase my bonus, but it would be nice to catch the "dangerous" cases in
>the main search and extend the pawn push moves if only I could find a way to
>identify dangerous from silly pawn pushes.
>
>Best wishes
>
>Roberto
Don't forget some of those magic combinations: 2 connected pawns on the 6th
defeat a rook, or other similar ones. I find Hiarcs very good at these types of
positions.
Albert Silver
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