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Subject: Re: Couple of chess programming questions

Author: Vincent Diepeveen

Date: 14:10:10 09/10/02

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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
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.

>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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