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Subject: Re: Evaluating Pinned Pieces

Author: Gerd Isenberg

Date: 14:03:40 05/19/04

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On May 19, 2004 at 15:40:35, Tom Likens wrote:

>
>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.

Hi Tom,

Yes, like other attacked and en prised pieces too.

>
>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).

In the opening, when a knight on c3 is pinned by a bishop on b4?
Quite normal. One should consider distance pinned piece to king and the for
instance whether the pinned piece may be attacked by a pawn.
And if not whether the pinned piece is defended by a pawn.


>
>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.
>

That makes sense.
Specially if the pinned side is to move, otherwise it should be handeled by
qsearch.


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

Same is true for other attacks, if you consider batteries in SEE you will
implicitly get that.


>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.

May be in conjunction with some king safety properties.
As always - carefully with huge values.

Cheers,
Gerd

>
>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.
>
>cheers,
>--tom



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