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Subject: Re: extensions

Author: Chris Whittington

Date: 14:53:55 12/26/97

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On December 26, 1997 at 11:25:11, Tord Romstad wrote:

>On December 26, 1997 at 02:40:01, Christophe Theron wrote:
>>
>>I gave up using these "threat evasion extensions", because I don't use a
>>SEE any more, and it was not clear that it strengthened my program.
>>Surprisingly, the improvement, if any, was a positional one. Not
>>tactical.
>>
>>Jean Christophe Weill describes some threats extensions (entropic
>>extensions) for the old Joker program in his PHD thesis (in french...).
>>He also gave up using them.
>>
>
>I believe that M-Chess uses lots of threat extensions. The program
>sometimes
>produces very long main lines with few captures and checks, even at low
>search
>depths.
>
>Tord

True. But if you play out the main lines, you'll see that at a critical
point, Mchess will show a deep opponent move and continuatiion. This
move will be 'bad' for the opponent, whilst being plausible. The
opponent will have had a better move, enough to refute the line.Often
the 'better' move will be seemingly obvious for a plausible move
generator, except that Mchess didn't create it, didn't look at it.
So at depth, Mhess is dangerously extending and/or pruning. My guess is
that the pruning is by 'explosion' count, ie the search is opening too
wide, so it gets pruned without looking at all possibilities -
dangerous, but often speculatively interesting.

Chris Whittington




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