Author: Omid David
Date: 15:28:20 09/10/02
Go up one level in this thread
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 >>>>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. >>>> >>>>>(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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