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Subject: Re: Expalain SEE (static exchange evaluator)?

Author: Bruce Moreland

Date: 21:46:23 10/25/00

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On October 25, 2000 at 23:26:15, Pham Minh Tri wrote:

>Hi,
>
>Could someone explain to me how SEE (static exchange evaluator) function works
>or show me books, old posts (when) or links to read about it?
>
>Thanks in advance.
>Pham

It is not mentioned in any books that I know of.

The routine works by evaluating the result of a series of captures on a
particular square.

You can either assume a first piece to move (if you are trying to predict if a
particular capture is productive), or you can figure out if a square is defended
given any possible first attacker.

The returns the best score available for the side to move.  In most cases, all
you need to know is if you lose any amount of material, swap, or how much
material you win.

In a quiescent search you can decide to prune captures that lose material.  You
can also prune swaps if you want.  And perhaps you'll decide to prune all
captures that don't seem to win enough material that you get your score back
above alpha.

It is actually very tricky to write a bug-free version of this routine.

You can also use it to order moves, either in the quiescent search, or at other
points in the tree.

There are a few rather obvious problems.  A piece may attempt a recapture even
if it is pinned.  Some people get really upset about this possibility, it seems
to me that the routine is a pretty rough estimate of what is going on, and is
apt to make mistakes worse than this.

Another problem is that you might not recognize that you have a battery, for
instance two rooks doubled on a file.  Missing an attacker's battery is the
worst case but it is easy to kludge.

bruce



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