Author: Tony Werten
Date: 00:40:47 09/13/02
Go up one level in this thread
On September 12, 2002 at 18:30:07, martin fierz wrote: >On September 12, 2002 at 16:50:38, Dieter Buerssner wrote: > >>On September 12, 2002 at 16:10:38, martin fierz wrote: >> >>>bestvalue = -mate; >>>for all moves do >>> { >>> value = -search(-beta,-alpha,etc); >>> bestvalue = max(value, bestvalue); >> alpha = max(value, alpha); >>> if(value>beta) >>> break; >>> } >>>return bestvalue; >>> >>>is there anything wrong with this? >> >>Pehaps you left it out on purpose - but this code snipped is missing an update >>of alpha. For example at the place, I suggested above. > >hi dieter, > >you are right, i left it out, half on purpose i guess. it just seemed irrelevant >to the return value. but it's in my code - although it's really unnecessary: in >MTD you always fail, so you never have to update alpha. but i have a compile >switch to go from a windowed search to MTD, and i never bothered to write an >MTD-only negamax function, although i could save an if or two there :-) > >>I see the same problem as you. Even when using strict fail soft search (I also >>consider other points mentioned in this thread, like lazy eval), I typically >>(but not allways) get back a score of X+1 for search, that fails high in the >>window X, X+1. I think, your suggestions "alpha-beta tries to do the least work" >>explains this. With a deep depth, and a complicated search tree, the X+1 score >>will be easiest to prove and most probably be proven first. > >i just made some more tests in positions where the score really swings much >(equivalent to winning a pawn in chess) and now i have seen jumps of more than >the eval grain, although only 2 or 3* eval grain, like the (0.00,0.01) search >returns 0.03. but most of the time it jumps as little as possible. This seems quite normal. I sometimes manage to get checkmate scores back to the root, but it doesn't happens very often. The deeper the searchtree below a move, the more likely the checkmatescore is "lost" somewhere. Tony > >cheers > martin > >>Regards, >>Dieter
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