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Subject: Re: Mate in 4 explanation

Author: Ed Schröder

Date: 11:18:45 10/08/97

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>In Reply to: Re: Mate in 4 explanation posted by Ed Schröder on October 08,
>1997 at 04:14:12:

>On October 08, 1997 at 04:14:12, Ed Schröder wrote:

>>>5rk1/1pnqb1r1/p2pRp2/2pP1PpQ/P1P1NpP1/3B1P2/1P1K4/7R w - - id=Shirov,A -
>>>Lillo Ferrer,J; bm=e4g5;

>>>I was reviewing this game with analysis mode with Rebel 8(K6-200)
>>>when the above position arose. For some reason Rebel could not find
>>>the mate in 4 move Ne4xg5. What is it about this position that might
>>>explain this? When I set Rebel 8 to "find mate in 4" mode it is found
>>>instantly.

>>This is one of the rare cases Rebel selective search fails.

>>You can check this to set Rebel8 on "brute force", see options.
>>Rebel8 will find Nxg5 M4 on ply 5.
>>Also SEL=1 / SEL=2 etc. will give improvements.

>>- Ed -

>>BTW, thanks for the position. I collect them and if there is a pattern
>>it's not so difficult to make improvements.


>Ed,

>Can Rebel9 quickly find the mate in 4 move Ne4xg5 using Normal
>Selection?

No, also Rebel9 suffers here.
Same story as Rebel8.

>Can Rebel9 find the mate in any move in other games using Normal
>Selection much faster and much better than Rebel8?

Set "Combination=ON" in the OPTION menu. Rebel8/9 will find
combinations generally 20-30% faster by special pruning.

During this year I have done some experiments finding combinations
faster. The idea: if the current game is a position and no moves
played yet, extend *some* moves from the move list with 3 plies.

I got wonderful solution times but if the algorithm failed a slow
down of 50-100% was noticed. I finally rejected implementation of
the idea because people would consider it as cheating.

- Ed -


>I don't expect Rebel chess program to be perfect, but I always feel
>better when Rebel chess program gradually gets closer and closer to
>perfection. :)

>Thanks,
>Eran :)
>Considering about buying Rebel9 in the future.



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