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Subject: Re: How to beat Gothmog

Author: Vasik Rajlich

Date: 01:29:25 01/09/04

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On January 08, 2004 at 12:01:56, Robert Hyatt wrote:

>On January 08, 2004 at 10:02:39, Anthony Cozzie wrote:
>
>>I've been trying to get some good test positions to rewrite my kingsafety with,
>>and playing Gothmog will give you those :) Usually Zappa is slightly better than
>>Gothmog.  It is stronger tactically (gets more nps and does not do all dubious
>>forward pruning) and its mobility is good enough that it plays reasonable moves
>>most of the time.  Usually Zappa will get its wins in the endgame, but Gothmog
>>will get in enough king attacks that the score is close.  During one of the test
>>games, this position came up (Zappa-white, Gothmog-black):
>>
>>[D]r2qk2r/pb4pp/3bn3/1P1ppp2/8/BQP5/P2NBPPP/R4RK1 b kq - 4 17
>>
>>Where Gothmog evaluated itself as +1, and Zappa thought it was about equal -
>>which is of course ludicrous since black has a big advantage. I was less than
>>happy with Zappa being blown off the board in 20 moves and not even realizing
>>it, so I wrote some code to evaluate control of the board.  But I made a mistake
>>and tuned it way too high.
>>
>>What was amazing was the result.  Every game went like this:
>>
>>Zappa pushes pawns
>>Gothmog sacrifices a piece for the pawns
>>Gothmog thinks its down .5
>>Zappa thinks its up 2
>>Zappa wins back pawns and the game with its extra piece/exchange
>>
>>Result: Zappa scores 86% - +18-0=7.
>>
>>Moral of the story: If you want to beat Gothmog, triple your space evaluation.
>>
>>anthony
>>
>>caveat: This was done under Arena, with the arena books, which need a bit of
>>work.
>
>Another moral:  Don't trade a piece for 2-3 pawns.  It will come back to
>haunt you more than it doesn't.

Bob,

do you have any statistics? It would be interesting to see the scores of an
engine as the piece vs pawns weight is adjusted. As I vaguely remember Crafty
has a huge piece weight, 4.2 pawns in middlegame positions (3 for the piece
itself, 1.2 for the bad trade bonus) even when the bishop pair is not involved.

In my program I use piece == 3.75 pawns if all material is on the board, and
piece == 2.75 pawns if all material is off the board, with everything scaled
linearly in between. The bishop pair, if it exists, is a separate bonus. Haven't
tried to tune it.

Vas



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