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Subject: Re: Couple of chess programming questions

Author: Omid David

Date: 11:45:27 09/10/02

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On September 10, 2002 at 14:30:56, martin fierz wrote:

>On September 10, 2002 at 09:26:14, Eli Liang wrote:
>
>>A couple of chess programming questions:
>hmm, i only wrote a checkers program, but here's my take:
>
>>(1) Are there any uses for ProbCut and/or Multi-ProbCut in chess positions where
>>the variance of leaf-nodes is low?
>
>i've tried multi-probcut and it works well in checkers. i never tuned it as much
>as my own pruning algorithm, and it doesn't perform quite as well - but it is BY
>FAR better than no pruning. i'll be trying to tune it in the near future. for
>games where the eval doesnt swing wildly, MPC is a fantastic algorithm.
>
>>(3) Reading Aske Plaat's search & re-search paper, it really seems like mtd(f)
>>is something of a magic bullet.  But I note it seems that more programs don't
>>use it than do (for example Crafty).  What is wrong with mtd(f) which Plaat
>>doesn't say?
>
>i'm using MTD. i tried windowed search, PVS and MTD. in my tests, in long engine
>matches, MTD performed marginally (no statistical significance...) better than
>PVS. it typically searched a low 1-digit % less nodes for a given depth than
>PVS.
>i don't know how to get a PV out of MTD. in normal searches, a pv node is where
>the value is > alpha but < beta. in MTD, you never get this condition.
>retrieving a PV from the hashtable is possible, but in all probability, you will
>not get the full PV. which is real bad for debugging if you want to know what
>the program was thinking at the time... i once asked here how to get a pv from
>MTD but got no answer - and if you can't get the pv, then that is a major
>drawback.

I haven't tried getting the PV out of MTD(f), but just a thought: why should
there be any problem in getting the PV out of hash table? Play the first move,
update the position, get the next best move from hash table, and so on... ?!


>
>>(6) Has anyone found any real "practical" benefits to fractional-ply extensions?
>
>yes. i tried recapture extensions of different depth, and half a ply gave the
>best result. don't ask me why, it's just an observation.
>
>aloha
>  martin



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