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Subject: Re: Toga Clone

Author: Alex Newman

Date: 20:34:44 03/09/05

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On March 09, 2005 at 23:13:30, Anthony Cozzie wrote:

>On March 09, 2005 at 22:30:05, Alex Newman wrote:
>
>>On March 09, 2005 at 22:10:58, Robert Hyatt wrote:
>>
>>>On March 09, 2005 at 21:19:51, Alex Newman wrote:
>>>
>>>>On March 09, 2005 at 21:12:52, Michael Yee wrote:
>>>>
>>>>>On March 09, 2005 at 20:27:09, Alex Newman wrote:
>>>>>
>>>>>>I can take the source code of Crafty and make an engine stronger then Crafty in
>>>>>>less then a week.
>>>>>
>>>>>Not to be (too) confrontational, but have you actually accomplished this feat,
>>>>>say, in a private experiment?
>>>>>
>>>>>There was someone here a while ago who was trying to get people to bet him a
>>>>>large sum of money that he couldn't improve crafty by some amount of points
>>>>>(maybe 100?).
>>>>>
>>>>>I'm skeptical of these kind of claims because if it were possible to improve
>>>>>crafty by that much, it would almost be commercial strength (according to WBEC
>>>>>ratings)... So why wouldn't that person just write a commercial-level engine
>>>>>from scratch (given that he has the last "secrets" anyway)?
>>>>>
>>>>>Michael
>>>>
>>>>I didn't say 100 ELO. I just said 'improve'.
>>>>No, I didn't try it. But try adding checks in quiescent, history and better
>>>>futility pruning, and you should get at least 30 ELO.
>>>>I think Crafty could be better in tactics.
>>>
>>>
>>>1.  crafty uses history.  always has.
>>>
>>>2.  older versions used checks in q-search.  you can see from the comments in
>>>main.c when they were removed.  The version with was absolutely no better than
>>>the version without, and the code was simpler without.
>>>
>>>3.  "better futility pruning" I don't know about.  It is already risky enough,
>>>but who knows what can be improved there...
>>
>>Thanks for the answer Prof. Hyatt. I have a great respect for you and Crafty.
>>
>>- By history pruning, I mean reducing search depth for moves with low history
>>value (many conditions apply of course). I know Crafty uses history for move
>>ordering, but am not aware you use it for pruning (didn't check the most recent
>>Crafties).
>>
>>- It's seems to be common experience shared by many that checks in q-search help
>>tactics, but again they shouldn't be done always. Some think that using always
>>R=3 and checks in q-search for null moves only is a good idea.
>>
>>- By better futility pruning, I mean doing pruning for nodes other then leafs,
>>but with much higher material margin.
>
>1. History pruning does NOT seem like a good idea.  The history table is
>completely unrelated to the current position, and yet you want to prune based on
>it?
>
>2. I personally use & like checks in q-search, but IMO its also possible to take
>the nodes saved by not doing them and put them into recap+mate extensions.
>
>3. Futility pruning only works with complete beancounters that have total
>positional terms of 1/2 pawn or so.  Plus, Bob already does lazy eval.
>
>IMO you aren't going to get 100 elo (or even 40) with search tricks.  You would
>have to improve the evaluation, which is the primary area where it fails in
>comparison to the commercials.  Which is obviously doable (Shredder & Fritz are
>doing something right) but not exactly 1 week's worth of work . . .
>
>anthony

1. History pruning is based on the probability that the move will cause a beta
cutoff. You keep track of the number of beta cutoffs for the move and if history
of beta cutoffs is very low, there is a good probability that move won't cause a
beta cutoff this time too. It is very tricky to find a right balance of pruning
benefits and errors it introduces, but it's obviously possible.

2. Why not do both, recap+mate+some (not all) q checks?

3. My tests (and it's also reported by others) indicate that futility pruning on
pre-leaf nodes works, and I don't see why not do it if using a lazy eval.




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