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Subject: Re: Couple of chess programming questions

Author: Omid David

Date: 13:03:35 09/10/02

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On September 10, 2002 at 15:33:30, Vincent Diepeveen wrote:

>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.
>In my draughtsprogram, of course draughts is a more complicated game
>than checkers and EGTBs play a smaller role there than they do in checkers.

What's the difference between draughts and checkers?! I thought "draught" is
merely the British equivalent for the word "checkers".

Here are the definitions of "checkers" and "draughts" according to the
Merriam-Webster Dictionary:

checkers \che-kerz\ n : a game for two played on a checkerboard with each player
having 12 pieces

draughts \drafts\ n, Brit : checkers

>But in any endgame i search at a 10x10 board already like 40 ply fullwidth
>easily. Middlegame like 20 ply fullwidth *easily*.
>At the very quick time controls i get 16 ply easily with Napoleon.
>In endgames i outsearch even good draughtsprograms by about 10-20 ply.
>Napoleon has saved many lost positions in the endgame, despite that i
>feel its endgame code sucks ass.
>The whole game of draughts and checkers is only about zugzwang.
>How can MPC work *anyway* if doing nothing is a GREAT thing to do
>in checkers?
>The first few versions of napoleon used to forward prune the
>last few plies and it was great to solve the most difficult tricks
>even faster (it already sees everything any world champion has
>found in tactics within microseconds of course). I concluded then
>that it worked, but i am of course a very stupid draughtsplayer.
>I am at the level of draughts like most chessprogrammers are in
>chess. I know all the things, but if i play i blunder away so many
>stones that i get sick of it.
>When i threw it out, it played much better.
>Can you explain why MPC works for you?
>Other question, not related to the above story, just general
>interest: how many professional checker players are there
>in the world now that tinsley is dead?
>Another question. What do you do in your qsearch for checkers?
>>>(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
>>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
>>>(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.
>>  martin

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