Author: Vincent Diepeveen
Date: 11:36:08 07/18/99
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On July 18, 1999 at 14:27:58, Dan Andersson wrote: >>We all don't doubt that MTD is a fine algorithm. Regrettably it only >>works for programs using an evaluation which gives very little deviation; >> >>See the score differences the first few ply in DIEP's lines: >> >>0.87 >>1.21 >>0.63 >>0.87 >>1.29 >>0.93 >>0.94 >>0.94 >>1.00 >>1.03 >>0.77 >>0.78 >>0.82 >>0.89 >>1.03 >>0.80 >>0.81 >>0.80 >>0.86 >>0.84 >>1.03 >>0.65 >>0.97 >>1.04 >>1.20 >>1.02 >>1.15 >>0.88 >>0.98 >>0.86 >> >>And those deviations still considering it's a position where there is >>not too much tactics. >> >>Getting the big fail low at 14 ply caused a jump from 1.03 to 0.65 >>which took 28.00M / 12.49 = 2.24 branching factor >> >>Just imagine the huge number of researches that MTD needs >>to get to 0.65! > >Probably one or a few re-searches only, I have not noticed that drawback in my >project. The problem is to implement lazy evaluation, thus the correlation >between pawn-values and evaluation as you mentioned. >I use a alpha-betaized evaluation function (it orders the evaluation factors in >a binary search and cuts off when it is out of alpha or beta boundaries and >returns alpha or beta) and save the state of the evaluation function in the hash >table if the position was not fully evaluated, to continue evaluating later if >needed. This way I get the benefits of MTD and lazy evaluation. i.e alpa-beta >evaluation cut evaluation time by 75% and it allows bootsrapping evaluation >values. A few researches is already more than the single research PVS needs at max! What lazy evalution are we talking about? I don't have lazy evaluation. Lazy evaluation doesn't work for me >> >>Because let's face it, what program *actually* use MTD currently: >> >>parallel version of fritz (?) : evaluation of it under 200 clocks >>cilkchess : evaluation also is very limited and >> definitely doesn't have huge scores, >> we all know that cilkchess evaluation is >> always very close to the number of pawns that >> it sees. >>SOS : same comment valid as for cilkchess >> >>So the programs using MTD currently have hardly anything in their evaluation >>not many things causing big scores, >>so claiming that MTD is doing a good job is only true when taking into >>account this restriction, which a lot of programs do not wish to have. >> >>Greetings, >>Vincent
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