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Subject: Re: Couple of chess programming questions

Author: Omid David

Date: 15:28:20 09/10/02

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On September 10, 2002 at 17:10:10, Vincent Diepeveen wrote:

>On September 10, 2002 at 16:03:35, Omid David wrote:
>>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".
>draughts is more commonly called: "international checkers". It is the only
>checker variation which gets played in several nations. checkers has
>all kind of forms and rules.
>draughts: 10x10 board
>checkers: 8x8 board
>draughts: you start with 20 pieces
>checkers: you start with 12 pieces
>draughts: capturing the longest string is a forced move
>checkers: you may chose
>draughts: if i capture a long string and do not end at the promotion
>          square, then my piece doesn't change into a queen. Only when you
>          LAND.
>checkers: if your piece gets over a promotion square, then you automatically
>          change into a queen (i do not know whether you capture further
>          LIKE a queen though).
>draughts: capturing backwards is legal.
>checkers: capturing backwards is not a legal move, except with queens
>so example in chess terms. white pawn on d4, black pawn on c3. In draughts
>white is forced to capture backwards (if no longer strings can get
>captured). In checkers this move is not a legal one. Only capturing forwards
>is legal with pieces. That removes major strategic problems in checkers
>when compared to draughts.
>the boardsize and the capturing backwards is really the most important
>difference, because it means that a queen is like unbeatable in checkers.
>In draughts promoting to a queen is way less interesting. In general
>3 pieces (and you start with plenty of them) is worth more than a queen.
>Of course loads of exceptions here especially near the endgame.
>The boardsize means not only that in checkers the fight starts way sooner,
>as the distance to promote from a1 to h8 is just 7 steps, in draughts
>it is 9 steps.
>The boardsize has more surprises than just that. For example when
>you have 3 queens versus 1 queen left on the board, in the general case
>that's a draw in draughts. It is a win in checkers if i understood well,
>with probably 1 exception if you are on the long diagonal.
>So the endgame in draughts is way way harder to win than it is in checkers.
>Another interesting difference is perhaps that the first 2 moves or something
>if i understood well are played at random in checkers by the arbiter.
>In draughts it is like chess: you start with the 20 pieces in a row and
>you make your own openings.

Thanks Vincent, for your thorough description.

>>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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