Computer Chess Club Archives




Subject: Evaluating Pinned Pieces

Author: Tom Likens

Date: 12:40:35 05/19/04

Afternoon all,

I've been reworking some of the evaluation elements of my engine
and one of the items I wanted to modify is the scoring of pinned
pieces.  So with that in mind I thought I'd share some my thoughts
on the subject (and maybe obtain a few new ideas in the process).

Currently, I'm including this items my pinned pieces evaluator.

1. If one side is pinning a piece *and* has the right to move, then use
   the SEE function to determine if the piece can be profitably captured.

2. If a piece is "absolutely" pinned (a Nimzowitsch term) penalize it.
   An absolute pinned piece can't move at all (e.g. a knight pinned to
   the king by an enemy bishop would be an absolute pin, whereas
   a bishop pinned to the king by a queen would not be since the bishop
   could move along the diagonal of the pin).

3. If the piece is absolutely pinned and the attacking piece's value is
   less than the value of the pinned piece (regardless of who has the
   move) penalize the defender a percentage of the difference between
   the attacking piece and the pinned piece.

4. If the attacker has a queen/rook, queen/bishop or rook/rook battery
   attacking the pinned piece then increase the penalty.

5. If multiple pieces are pinned increase the penalties. Also if multiple
   pieces are pinned then accessed the pinned side some percentage
   of the *largest* pinned piece from either 1 or 3 above.

As I mentioned earlier, I'd be interested in how others handle pinned
pieces.  I'd also be interested in just hearing thoughts on the above and
if I've missed anything obvious.


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