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Subject: Re: passed pawn evaluation.

Author: Robert Hyatt

Date: 06:33:20 01/13/04

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On January 13, 2004 at 05:23:24, Tord Romstad wrote:

>On January 12, 2004 at 20:21:45, Robert Hyatt wrote:
>
>>You can hash _everything_ about pawns, just so your scores have _only_
>>information about pawns in them.
>
>But scores of any kind are *never* computed only on the basis of the
>locations of pawns.

Sure they are.  When I say "score" I mean something that is used to
compute a score.  Some things can be scored directly without regard to
pieces.  Weak pawns.  Isolated pawns.  Etc.  If you want those scores to
depend on pieces, that is fine.  Just score the pawn part, hash that score
part, and also save the flags that tell you that you have pawn scoring that
needs piece values added in.  Then if you get a pawn hash, you get a partial
score, plus flags telling you what is passed, what is a candidate passer,
where you have a majority, where you have weak pawns, and then you use those
flags later, but you avoid the cost of computing the flags...

> That's why it doesn't make sense to store any scores
>in the pawn hash table.  The proper way to use a pawn hash table is to
>store some of the pawn structure related information you need to
>compute scores.

Again, it depends.  I look at both the king and queen-side pawn shelters for
the king, and add up "defects for each side.  I store these two values in the
pawn hash entry and later use them to compute king safety scores when I factor
in material on the board, and how many pieces are close to a king that is
exposed.  But _some_ of the scoring is piece independent.  IE doubled pawns
have nothing to do with whether you have all your pieces or none.  Ditto for
the base isolated pawn score.


> I store the locations of all passed, isolated,
>double and backward pawns, the number of pawns on black/white squares
>for each side, the number of blocked (by enemy pawns) pawns on black/white
>squares, the open files, the type of central pawn structure (with
>possible values like OPEN, CLOSED, SEMI_CLOSED, W_STONEWALL, B_STONEWALL,
>FRENCH and so on) and some other similar stuff.  My pawn hash entries
>are quite big, currently 128 bytes.
>
>Tord



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