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Subject: Re: Static Exchange Evaluation (SEE) for pruning in quiescence (?)

Author: Robert Hyatt

Date: 07:21:12 08/19/03

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On August 19, 2003 at 05:04:58, Omid David Tabibi wrote:

>On August 19, 2003 at 04:12:45, Tord Romstad wrote:
>>On August 19, 2003 at 02:48:36, Omid David Tabibi wrote:
>>>It seems that some programs use Static Exchange Evaluation in order to prune
>>>losing captures in quiescence search.
>>Not just some.  Almost all strong programs do this, I think.
>>>In the following position, an SEE will deem the move 1.Rxd7 a losing capture, and it might
>>>get pruned in quiescence. However, in fact this is a winning capture since Qf6 is attacked
>>>after 1.Rxd7. How do such programs solve these kind of problems?
>>They don't (or at least most don't).  On the other hand, the significant extra
>>speed gained
>>by not searching all captures help them find a lot of other tactics which they
>>wouldn't have found.
>>Try it yourself.  I am almost certain that you will find that excluding losing
>>from the qsearch is a big win.
>But a good SEE will be quite costly by itself. For example:
>[D]3r2k1/pp1r1qpp/2pb4/5p2/3R1P2/8/PPPR2PP/3Q2K1 w - - 0 1
>My engine has information about all attacked squares, e.g., it knows that d6 is
>attacked by a white rook and defended by a black rook. However, I assume that an
>SEE should be able to find out that Rxd6 is a winning capture. This needs a more
>extensive processing of backed-up attacks (e.g., Rd4 is backed up by Rd2 which
>is backed up by Qd1, and Rd7 is backed up by Rd8). I'm afraid this is too costly
>a process.

Not necessarily.  Crafty has _always_ handled this case with no problems.  As
did Cray Blitz.  As does most other programs I'll bet.  When you do the
capture analysis, and you "use" a piece, you just look behind that piece (only
in one direction) to see if there is another piece that is not attacking the
target.  The expense is trivial.


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