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Subject: Re: mate threat extension/null move

Author: Stuart Cracraft

Date: 12:18:22 09/25/04

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On September 25, 2004 at 14:59:07, Zach Wegner wrote:

>On September 25, 2004 at 14:46:06, Peter Fendrich wrote:
>
>>On September 25, 2004 at 13:51:39, Zach Wegner wrote:
>>
>>>>When you find a mate it first will get x > beta... Right?
>>>>Then you will never reach the following statement.
>>>>/Peter
>>>
>>>No, this is when the side to move gets mated, giving a score < -MATE + MAXPLY.
>>>
>>>Zach
>>
>>Right but I meant that return beta will not show -MATE+MAXPLY one ply up.
>>This nulmove only code, however, and the answer is dependent of what's happening
>>in the alpha/beta stuff later on...
>>/Peter
>
>Sorry, I misunderstood you. But the mate threat code is typically not (x < -MATE
>+ MAXPLY) but (x == -MATE + ply + 2) so that first when the side to move is
>mated it returns -MATE + ply (ply being 2 more than where the nullmove is
>called) and then at ply + 1 it returns MATE - ply (this is a simple
>change-return val instead of beta at a fail high)


But doesn't returning -MATE+ply from search() mean that the program
might postpone making a mate since it is not returning -MATE+depth
and so the ply is increasing and so more credit for deeper mates
whereas depth is decreasing so more credit for more shallow mates?

Stuart



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