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Subject: Re: Forced moves

Author: Ian Osgood

Date: 13:44:47 07/30/99

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On July 29, 1999 at 20:47:14, Dann Corbit wrote:

>On July 29, 1999 at 18:58:12, Ian Osgood wrote:
>>Do other program authors curtail the search when there is a forced move at the
>>root?
>Crafty does.  It causes havoc with the Chess Analysis Project.  Fortunately,
>Hiarcs will actually process such a position if I ask it to.
>
>>How do you detect that a root move may be forced?
>Umm.. You have no other choices but one?
>
>>Could you compare the values of the best and second-best root moves after a
>>search iteration to detect a forced root move?  (Granted, the second-best score
>>won't be accurate due to alpha-beta, but I figure that if the difference was
>>greater than a queen's value, you could still conclude that the best move was
>>forced.)
>Here is how I would detect it:
>0.  Am I in check?
>1.  Is there only one way to get out of check?
>If so, then the move is forced.  Otherwise, the move is not forced.

I was thinking of a looser definition of "forced" (which subsumes one legal
move, of course).  Obvious recaptures would be included, more along the lines of
crafty's "easy" moves with 1/3 search time.

Ian



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