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Subject: Re: SEE and pin detection

Author: Gerd Isenberg

Date: 01:00:54 09/01/04

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On August 31, 2004 at 19:55:39, Dan Honeycutt wrote:

>On August 31, 2004 at 14:30:03, Gerd Isenberg wrote:
>
>>On August 31, 2004 at 12:03:13, Dan Honeycutt wrote:
>>
>>>On August 31, 2004 at 04:50:27, Richard Pijl wrote:
>>>
>>>>
>>>>I'm feeding both pinned and pinning pieces as a bitboard to my SEE routine.
>>>>Whenever a pinning piece enters the exchange (easy check with bitboards) I'm
>>>>examining whether the pinning piece releases a pin, or that another piece
>>>>becomes the pinning piece.
>>>>Of course, there are positions where this misevaluates as well, but generally it
>>>>gives a better value.
>>>>The penalty for taking pins into account in the SEE is not that big when you're
>>>>already have those bitmasks available for evaluation purposes.
>>>>I only use the pin-aware SEE in Qsearch as I don't have the pinned/pinning
>>>>bitmasks available in inner nodes (something to try I guess, e.g. to use the
>>>>pin/pinning data also in moveordering).
>>>>
>>>>Richard.
>>>
>>>Thanks Richard for the good ideas.  I'm using my move generation pin routine
>>>which produces a bitmap of pinned pieces and for each one the squares where they
>>>can go - a ray from the friendly king to and including the pinning piece.  So
>>>right now I don't have the pinning piece but I can get it pretty cheap.  I'll
>>>tinker with this.
>>
>>Hi Dan,
>>
>>sorry for my confusing answer, i didn't got the point.
>>I thought it had something to do with traversing order of the knights in your
>>implementation. Thanks to Richard i'll hope i have it now ;-)
>>
>>Your SEE-routine didn't recognize after Nxg5 Qxg5 the released pin and is
>>therefore to "pessimistic". Richards idea seems quite fine, even not perfect it
>>works in an "optimistic" way.
>>
>
>Right.  My no-pin SEE doesn't know the knight is pinned, my pin-aware SEE
>doesn't realize the pin is broken.
>
>>>
>>>Having pins for both sides available at all times opens the door for me to add
>>>pins to my evaluation for no extra cost.  Do you just add a bonus per pin or do
>>>you try to make some determination of the worth of the pin?
>>
>>Some possible heuristics: pinned on own or opposite side of the board, distance
>>to own king, attackable by enemy pawn considering own guard pawn, if not,
>>defended by pawn or considering SEE-like attacker and defender.
>>
>
>I'd figure pinned on opposite side = worse than pinned on own side and attakable
>by enemy pawn = very serious.  Not clear on distance to the king - is it worse
>if farther away?  (I'm thinking of the opening where knights close to the king
>routinely get pinned, most of which are pretty penny-anty)

Yes if distance to the king is <= two and no enemy pawn may attack the pinned
piece is almost not so dangerous.

>
>
>>>
>>>Doing pin-aware SEE only in QSearch makes a lot of sense.  I hadn't thought of
>>>that.
>>
>>Why?
>>
>Why what?

Sorry, i meant doing pin-aware SEE only in QSearch.

>
>Why it makes sense:  In normal search a good move may get ordered lower do to a
>bad SEE but I'll still find it.  In QSearch it may get discarded.


I understand, but for evaluation and probably move ordering issues the
information of pinned pieces is usefull in normal search too. Together with some
other tactical "indicators" like hanging, or enprised pieces etc. it is usefull
to decide on reductions, extensions and/or probably doing nullmove.

>
>Why I hadn't thought of it:  What can I say?  Age.  Too many cobwebs where there
>should be electrical activity.

Hehe, i had similar phenomena, for instance as i implemented static mate
detection ;-)

Cheers,
Gerd

>
>Best.
>Dan H.
>
>>Cheers,
>>Gerd
>>
>>>
>>>Thanks again.
>>>Dan H.



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