Computer Chess Club Archives


Search

Terms

Messages

Subject: Re: Evaluating Pinned Pieces

Author: Tony Werten

Date: 09:22:58 05/20/04

Go up one level in this thread


On May 20, 2004 at 09:52:56, Tom Likens wrote:

>On May 20, 2004 at 05:48:25, Tony Werten wrote:
>
>>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.
>>>
>>>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.
>>
>>I don't think 1 and 3 should be evaluated as pinned pieces but just as hung
>>pieces.
>>
>>Furthermore 3 should be adjusted. If the "pinned piece" is higher than the
>>"pinning piece", you should evaluate the square of the "pinned on piece". (So
>>just assume the hanging piece will move)
>
>Hello Tony,
>
>I agree to a large extent with most of your comments, but I'm not sure
>I understand this point clearly. I believe what you're saying is that that if...
>
>a) the pinned piece is more valuable than the attacking piece it will need
>    to move and so...
>b) when it moves evaluate the attack on the piece it was pinned against
>
>This is correct in general, except when a piece is absolutely pinned
>against the king (as in case 3).  Also, if the piece being pinned is more
>valuable than the piece it is pinned against then this wouldn't apply
>either (impossible of course, in the case of the king but not in the more
>general case).

Yes, sorry, it was incomplete. You should score the lowest one, wich automaticly
takes care of an absolute pin, since that would score +inf for the "pinned on
piece", wich means you always take the see value of the pinned piece.

>
>>4 is needed to evaluate the pins correctly, and 5 won't be hit very often.
>
>I use 5 as one of the measures for determing the "turbulence" of a
>position, which is then further used to determine how safe it is to
>prune various positions etc.

That would be the best ( and only ?) use for it.

Tony

>
>--tom
>
>>Tony
>>
>>>
>>>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



This page took 0 seconds to execute

Last modified: Thu, 15 Apr 21 08:11:13 -0700

Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.