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Subject: Re: Hashtable and avoid null move

Author: Volker Böhm

Date: 04:56:47 05/10/04

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>
>      if (type == UPPER && depth-R <= draft && tableval < beta)
>        avoid_null = 1;
>
Hi,

I don´t understand the "depth-R" part, I would have written "... && depth <=
draft && ...".

You use the nullmove to predict if a search at current position with depth
"depth" will bring a score >= beta. If so, you are finished. If now the hash
tells you that a search with "depth" will not bring a score >= beta (upperbound
< beta) you shouldn´t do null moves. In the best case the nullmove is just waist
of time, in the worst it gets a wrong cutoff. Agree?

Even if a search of depth "depht-R" does not give a score >= beta a search with
depth "depth" could. Don´t you miss valueable nullmove cuttoffs if you use
depth-R hash entries to predict that nullmove will not be effective?

Is "depth-R" systematically the best solution or "just" a little optimizaion
that could change for other engines?

Greetings Volker



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