Author: Robert Hyatt
Date: 14:37:25 12/25/99
Go up one level in this thread
On December 25, 1999 at 13:27:45, John Hendrikx wrote: > >>>Now, I can think of the following four standard >>>enhancements to a search function (there are >>>probably some more): > >>>null move >>>killer move >>>extensions >>>hash tables > >>I don't see 'capture moves'. They are _critical_ and have to be done >>before any other move (except hash table move). > >As it happens, I've started playing around with move-ordering as well, >and giving priority to captures increased the speed by a factor of 3 >(I already made sure that the PV was the first move tried). > >I also found that trying pawn-moves (not captures) after all other moves >gave me another nice speed up (about 30%). Currently I have this order: > > 1. PV > 2. Captures (ANY captures -- no SEE algorithm involved (yet)) > 3. Piece moves > 4. Pawn moves > >No killer/history heuristic yet. > >I don't know if sorting Pawn Moves last will hold up in later stages of >the game (I only tested the beginning) -- I could give Pawn Moves scores >depending on how far up the board they are though... > >I've tried adding null-moves as well, but haven't been very succesful. I >need some more to go on before I can get it right, but I can't find good >examples or descriptions of them. So far what I've tried is to try a >null-move before doing any real moves at a certain level of the tree, and >searching the null-move to the same depth as usual; my problem is that I >don't know what to do with the returned score. From what I gathered one >should create a cut-off when the score is 'not so good' even while doing >two moves in a row.. it didn't work for me though. It was far slower (1.5 >times) with the same results, and only a few dozen null-move cutoffs at >6 plies orso. When I increased the cut-off point by half a pawn in favor of >more null-move cut-offs all I got was a bunch of very bad moves. > >What can one reasonably expect to win if one is allowed 2 moves in a row? >Should null-moves be tried for both black and white? The game. IE I would be more than willing to play Kasparov if at one point (of my choosing) in the game I can play two moves in a row. That is a really serious advantage. If you reach a position where two moves in a row doesn't cause you to fail high, your position is _bad_. > >>killers and history moves are similar. history is a more global concept, >>while killers are more local to specific parts of the tree. I use both as >>with killers you can try them before generating all the non-capture moves. > >>>If 1), how would you order the above in decreasing >>>order of effectiveness? >> >>I do the following: >> >>1. hash table move > >Is that the same as the Principle Variation? Yes and no. While searching the PV, it is the same. But in non-PV positions it is simply the move that was found best in this position when it was entered into the hash table... > >>2. captures with expected material gain >= 0 (using the classic SEE approach >>to determine expected material gain). moves are sorted by expected gain. >>3. killer moves >>4. 4 history moves >>5. remainder of move list. > >John.
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