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Subject: Re: evaluation tuning tricks

Author: Volker Böhm

Date: 03:49:38 03/17/04

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On March 17, 2004 at 04:58:06, Peter Alloysius wrote:

>what are tricks for evaluation tuning so that it could
>search less nodes?
>
>i noted that my engine use exactly same move ordering scheme as
>crafty but it still search much more nodes.
>my engine also use adaptive null move, and futility pruning.

Make sure that you use the same extension rules than crafty if you whant to
compare.

>
>so i think the problem is on evaluation tuning.
>i heard that tuning evaluation function can reduces node searched,
>so what's the trick?
>
>i will appreciate any answer. thanks
>sorry with my poor english.

All you can do is to Build a stable eval. I.e. an Eval that don´t "jump" if you
make the next (non-hit) move.

Identify your biggest eval factors and find a way to "smell" changes on them.
Trivial Examples that will explain it:

Mate -> king attack -> king security -> superior pieces at kingside
Promotion -> passed pawn (advanced/not advanced, blocked/non-blocked) -> hidden
passed pawn -> superior advanced pawns -> advanced pawns
Material  -> pieces that have to flee/pinned pieces -> defendet pieces/attacked
pieces
...

I have a "reference-game" that I evaluate with fixed depth on every change of
eval. If ever the amout of nodes searched raises I have to check the changes.
Mostly a bad change of eval leads to  increase of nodes searched.

Greetings Volker



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