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Subject: Re: hard question about SEE and crafty - it only needs 4 iterations ?

Author: Tord Romstad

Date: 11:04:10 01/09/04

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On January 09, 2004 at 12:51:47, Robert Hyatt wrote:

>You are worrying about making the lug nut on one wheel perfect, when the rest
>of the truck is falling apart.  SEE is _inherently_ inaccurate.  It does not
>pay attention to  pinned pieces, overloaded pieces, etc.  It is used to choose
>moves and move order searched by the q-search, which is _also_ full of holes,
>it doesn't look at moves that pin pieces, unpin pieces, xray/skewer pieces
>and so forth.

This is all true, but you can still do better than just giving up.

In theory it is of course possible to write a very complicated SEE which
evaluates the positions Uri presented correctly.  But such an SEE would
probably be so slow that it is not worth the effort.

What you can do, however, is to estimate the complexity of the position
(I do this as part of my evaluation function) before generating captures
and using your SEE.  Then your engine can make decisions like "oh,
there's a lot of hanging, pinned and overloaded pieces here, I shouldn't
trust the SEE at this node", "this is easy, my opponent has this big
juicy hanging piece just waiting to be eaten, none of my pieces are
pinned or hanging, let's just return a fail high search at once" or
"looks like there could be a back rank mate here, let's search checks
as well as captures".

By using such techniques, it is possible to have a qsearch which is
*more* accurate than a minimalistic qsearch with a simple SEE, while
searching *fewer* nodes in most positions.  At some qnodes you search
all captures, at some nodes you only search winning and equal captures,
and at some nodes the SEE gives a sufficiently accurate estimate that
you can just return a score without searching any moves at all.

Tord





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