Computer Chess Club Archives




Subject: Re: Square-of-the-pawn

Author: Robert Hyatt

Date: 11:30:40 01/13/98

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On January 13, 1998 at 12:57:43, Stuart Cracraft wrote:

>Years ago I remember reading something where Dan and Kathe Spracklen
>(remember them?) said that the addition of the square-of-the-pawn
>rule-of-thumb to their program increased is strength significantly.
>(I think they said a whole USCF class!)

It wasn't Dan and Kathe, it was me.  This was something I added to
"blitz" around 1970 or so.  Back then, it was searching 4-5 plies
max, and had a USCF rating of around 1400, playing in local tournaments.
But it kept getting hoodwinked in endings where the opponent would offer
something to decoy the king away, and then the pawn could scamper in
before the king could catch it.  It was winning middlegames, but losing
endgames.  Remember too, that this was in the days of 4-5 plies of
selective search, with *no* extensions and not even a real quiescence
search.  So this was a critical issue.

When I put this in, its overall rating climbed to 1600, and stuck there
until I "went exhaustive" in 1977 when its rating jumped to 1800+, and
then when I "went Cray" in 1980 we went to 2200+.  (All official USCF
rating numbers, not TPR or something else).

>Anyway, now that I have passed pawns stored in my pawn transposition
>table, it would be simple to use them in some calculation to get a
>square-of-the-pawn assessment.
>How have you implemented square-of-the-pawn? Are there any strange
>implementation issues or things to watch for? What kind of strength
>improvement did your program get and how did you determine this
>strength improvement.
>Thanks ahead!

The issue is only "can the king catch the pawn?"  If the answer is no,
score+=queen-pawn, if the answer is yes, then there's no bonus.  You
need a search, because it is possible to have two passers, neither of
can outrun the king, but neither of which can be captured either because
capturing one takes you out of the square of the other...

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