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Subject: Re: Shredder wins in Graz after controversy

Author: Robert Hyatt

Date: 17:12:22 12/09/03

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On December 09, 2003 at 17:18:53, Gerd Isenberg wrote:

>On December 09, 2003 at 14:07:21, Robert Hyatt wrote:
>
>>On December 09, 2003 at 13:50:14, martin fierz wrote:
>>
>>>On December 09, 2003 at 12:32:15, Robert Hyatt wrote:
>>>[snip]
>>>
>>>>I don't see how this matters since the engine doesn't understand the concept
>>>>of "my opponent might make a mistake."
>>>
>>>and this is exactly where the problem is. i understand it, and you understand
>>>it, but 99% or 100% of all chess engines don't understand it. which doesn't
>>>change matters: if you have a draw "in hand", you don't claim it. you let the
>>>other guy decide whether he claims it or makes a mistake. computers will say the
>>>position is 0.00. it is >= 0.00. of course it is 0.00 if the opponent plays
>>>well. but you don't know that he will play well, so you have him prove it.
>>>even if your engine doesn't understand the concept, your opponent can still make
>>>a mistake :-)
>>
>>yes.  But back to the real-world.  Alpha/beta doesn't do that.  It only notices
>>that the draw is the best score it can produce.  It has no way to pass back
>>information like "this is a repetition, but the opponent can blunder and
>>lose if he isn't careful" vs "this is a repetition, and if I don't claim it,
>>my opponent might choose to deviate and win, because he screwed up to let me
>>repeat the position for the second time."  IE the Jonny case.  I only know
>>it is a draw, and I would claim it (using alpha/beta) because I can't tell
>>what happens if I don't, as the search doesn't tell me.
>
>If you detect the 3-fold repetition  direct after your best root move so far,
>you have the safe draw (already detected after a depth one search).
>You may claim it or leave it to your opponent.
>
>What about some a further special searches skipping the repetition detection
>after root moves and huge contempt factors for further repetitions and to decide
>on the outcome of that searches whether it is necessary to claim the draw
>according to rule 92a) immediately (eg. in the Shredder case < -10 ;-) or to
>pass it. And it leaves the option to take some time and to probably find a
>winning combination with another move ;-)

And the point of that would be exactly what?  IE the opponent does a
search when you elect to not claim the draw, it notices the score is
much worse than draw, so without playing a move, it claims the draw
itself, which is perfectly legal...  I fail to see why it would be
useful to do anything that depends on your opponent doing something
totally stupid for it to work at all.  It's just wasted code that has
to be debugged...

>
>
>>
>>
>>>
>>>[snip]
>>>
>>>>>there are so many positions where both sides are forced to repeat, because they
>>>>>lose if they don't. e.g. i sac something, get a perpetual and if you go on the
>>>>>wrong square with your king i win. if i make a quite move you defend against the
>>>>>perpetual and win. this is a very common situation. i will definitely not claim
>>>>>the 3fold repetition in such a position, because you just *might* go on the
>>>>>wrong square. i can't do anything about it, the game is a draw. but since you
>>>>>can still go wrong i won't claim the draw just yet, i have no reason to. i can
>>>>>always claim it later.
>>>>
>>>>This does not happen in computer vs computer games.  They resolve this at the
>>>>_second_ repetition, they don't have to wait for the third and then play through
>>>>it to fix the problem.
>>>
>>>replace "this does not happen" with "this should not happen in c-c games". for
>>>example, you can imagine the situation where it's hard to see that avoiding the
>>>draw is a loss, in fact, it first looks like a win. you're searching that move
>>>which avoids, then you fail low, allot more time, and the next time you search
>>>that position you're in time trouble and play the move which looks like a win
>>>but is a loss. this is possible if you clear your hashtables, for example....
>>>besides, there is always the possibility of a bug. e.g. shredder repeated the
>>>winning position 3 times, instead of 2. according to your theory, "this does not
>>>happen". of course it does, it was a bug. if it happens to SMK, it can happen to
>>>anybody ;-)
>>
>>Shredder didn't do it intentionally.  It had a bug.  Jonny intentionally said
>>"I want that draw, as any other move loses".  It seems pretty clear to me how
>>it should have been handled.
>>
>>>
>>>cheers
>>>  martin



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