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Subject: Re: Pawn promotion defense

Author: Bruce Moreland

Date: 00:23:37 10/08/99

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On October 07, 1999 at 19:51:56, Scott Gasch wrote:

>Hello,
>
>My engine has a real problem defending against pawn promotions.  The way it
>works now I have a PSQT that makes advanced pawns more valuable.  I also do an
>extension threatoning pawn advances (to the 6th or 7th row) in the middlegame
>and endgame.
>
>Bob had mentioned using a SEE on the pawn push to see if it is safe.  I also
>think my eval shoud do a better job of identifying threat pawns and scoring them
>appropriately.  Right now a pawn on the 7th rank gets a PSQT bonus for being far
>advanced, another bonus for being passed...
>
>How do people handle pawn promotion defense?  Every time I lose a game it is
>because it messed this up.  Often it has the oppertunity to sack a knight or
>something to kill the pest but it doesn;t do it because it doesn't see deep
>enough to realize the pawn will definately queen in like 8 moves or whatever...

The problem happens because a passed pawn represents a long-term threat, which
programs have a hard time dealing with.  You see the same sorts of mistakes when
humans sacrifice pieces in your king position.  For a while you think you are up
material, then boom.

A passed pawn can be worth -1, if it is a weak pawn that's going to be
collected, or +8 if it is going to turn into a queen.  That's too much spread to
handle with a simple-minded heuristic value.

Search depth will help a bit, but I don't think there is a simple solution to
this problem.

You can catch some cases where the pawn is likely to be weak or strong.

1) Pawn blockaded by enemy king.

2) Advanced pawn supported by friendly king.

3) Connected passers on the 6th or 7th.

4) Rook behind passed pawn.

5) Etc.

I would think that adding knowledge of of these features will help a little but
it won't solve the whole problem.

bruce



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