Computer Chess Club Archives


Search

Terms

Messages

Subject: Re: Q: pawn hash?

Author: Robert Hyatt

Date: 07:40:41 07/20/99

Go up one level in this thread


On July 20, 1999 at 02:20:03, Scott Gasch wrote:

>
>Ok, I've heard people talking about pawn hash tables and this got me thinking
>about them.  I am not sure how to do it --
>
>1) if you just hash 8 pawn locations and an associated evaluation that is pretty
>easy.  It's a nice small number, can fit in memory, etc... However, you can't
>recognize passed pawns becasue you don't know where the enemy pawns are?
>


hash all 16 pawns into one signature... then this isn't a problem..


>2) if you make a table with all 16 pawns in all possible configurations I
>calculate a total of 1120853258472 possibilities.  That requires quite a bit of
>memory... ;)


you will find most of those don't really occur... and in a good chess engine,
pawn advances are treated cautiously because they permanently affect pawn
structure and most programs weigh this heavily.  I usually see a 99% hit rate
on pawn hash probes, for example...  This means that only 1% of the positions
need a full pawn-structure analysis.  So that I can put _anything_ in the pawn
structure analysis I want since it costs essentially nothing.





>
>3) do you mean just hash the recent scores for pawn structures?  This way any
>node that has the same pawn structure anywhere in the tree can get the pawn
>score instantly?
>


yes...




>Thanks,
>Scott



This page took 0 seconds to execute

Last modified: Thu, 15 Apr 21 08:11:13 -0700

Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.