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Subject: Re: Couple of chess programming questions

Author: Vincent Diepeveen

Date: 12:33:30 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.

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.

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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