Author: Juergen Wolf
Date: 09:42:05 08/15/03
Go up one level in this thread
On August 15, 2003 at 06:33:56, Bo Persson wrote: >This article is one step on the way to his thesis. There he explains it in more >detail, but the results are still shown only for a particular engine searching a >set of test positions to a fixed depth. The fixed depth part is also a >limitation. > >Generalizing the result is material for another thesis, or three. :-) > i would probably have used a different headline or put at least a questionmark behind the headline >> >>Nevertheless i think its an interesting idea worth to be tested . I like the >>simplicity of MTD. I read some previous threads and there seems to be some >>programs where MTD is not of any benefit. Is it correct to assume that those >>programs are using IID (question 3). My understanding is that IID is not useful >>in zero-window search and is used just in case no move was found in the >>transposition-table. Did somebody ever compare Negascout+transposition+IID vs >>MTD (question 4)? My thought is that IID might provide sufficient >>"compensation". > >I don't do IID, just ID. :-) you are using negascout ? > >> >>My program so far used a window of +/- 0.2pawns for the 1st search, in case of >>a fail high i redo another search with a window of 1.2 pawns and in case this >>still fails high i'm using the max-window. I implemented MTD (work of minutes >>and is working) and intend to do some extensive benchmarks. >> >>Plaat also mention that the MTD-grain is important. My program has an >>eval-grain/stepsize of 1/1000 pawn. Is there a benchmark comparing success of >>MTD (using different settings of step-size) wrt to grain of eval-function >>(question 5). > >I think he is right here. You could very well evaluate in millipawns, and then >truncate to the result to centipawns. This helped me reduce the number of steps. > >>For example if i have a grain of 1/1000 in eval - function , is a >>stepsize >>of 10 , 20 , 40 (1000 points = 1 pawn) better than "worst case" 1 ? > >Someone (lost the name right now, sorry) showed here a couple of years ago how >to use an exponentially growing/shrinking step size. > >I start at stepsize 16 (because that works better than 8 or 32:-) and then >double the size for each step, until the first overstep. I then reduce the >stepsize (stepsize /= 2 ) for each successive step, forwards or backwards, until >I zoom in on the final value. Here 1 pawn = 100 points. > thanks , i missed this thread. probably entered wrong keywords. i'll try again >> >> >>I read that in case of MTD its important to store lower-bound AND upper-bound. >>So far my program just stores one value. Did somebody compare these two >>approaches (question 6)? > >Yes, it works much better with both bound. Probably has the biggest effect if >you continuously overstep in both directions while zooming in on the score. > >However, for me Negascout also works better with two bounds! > >> >>Wrt to transposition table i read statements that using a move from a fail-low >>search should not be taken as preferred move. What are the general experiences >>on this (please describe feature set of program, question 7) ? > >If all moves fail low, which move should we prefer? currently i'm using the move with a result as close as possible to alfa. if the move was the hashmove of a previos search (fail-high-move) than this move does not get overwritten. > >> >>A read a long time ago an article proposing , in case that a Zero-window search >>provides a fail high (a better move found than the best-move-so-far), it might >>be worthwhile not to do a full research just to find the exact value. In case >>another move beats the best-value , both moves have to explored agained to >>decide whether move 2 or 3 is better. Are there any statistic/experiences >>available (question 7)? > >Guess it depends! :-) > >If you don't resolve the single fail high move, you might have a worse starting >point for the next depth. You win some, you lose some. > >Most people also want to see the evaluation displayed during and after the >search... > >> >>i intend to make those benchmarks with my own program in order to decide which >>is the best setting for my program, but would like to compare my results with >>the "rest of the world" ( or set my expectation right) >> >>kind regards juergen wolf > > >Bo Persson >bop2@telia.com
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