Author: scott farrell
Date: 20:54:31 11/30/02
Go up one level in this thread
On November 30, 2002 at 23:38:44, Russell Reagan wrote: >On November 30, 2002 at 20:55:54, scott farrell wrote: > >>if it was 3.03-3.77 as you suggest, a few things would need to have happened: >> >>Nf6 would have needed to fail low >>Possibly several other moves would have needed to fail low >>Nf4 failed high >> >>So what I am saying is that, for this analysis only, that a wider window would >>reduce the chance of Nf6 to fail low, and hence why I think it was a >>narrow/narrower window. > >Ok I'm still learning and trying to understand this better. Let's take an >example. Let's say that in this example from Monsoon, we got the result after 10 >plies of Nf6 with a score of +3.02. Now when we do our 11 ply search, what do we >set the aspiration window to? If 'score' is the score from the previous ply >(which is +3.02 in this case), and 'n' is the width of the search window, then >do you set your aspiration window to (score, score+n)? Bob gave the example of >using (0,2*score). Obviously there are a lot of ways you could set your >aspiration window. How do you know what is safe and what is not? For example, I >suggested (3.02,3.77) and you said that it might be unsafe, and other things >would have needed to happen for this to be safe. So how do you determine how to >set the upper and lower bounds for your aspiration window? I dont think I said it was 'unsafe' I said it didnt explain the output of Monsoon. I think Robert says in crafty he does alpha=value-0.3, and beta=value+0.3. Anyway, there is clearly no 'correct' value for this (nor anything else in chess programming). It largely depends on what your strategy is, ie. what are you going to do on a fail-low or fail-high, are you trying to work out/infer anything else? I am setting the alpha value to a low enough figure, so if I get 5 fail-lows, I panic on the clock, and request more time to find some sort of solution. So the value I choose needs to be enough to set off my panic, without too many false alarms. I have been using 1/3 of pawn (which is similar to Roberts 0.3 by co-incidence). If the score drops for the same move by 0.3, then that is my partial panic mode, if it is 1 pawns, 5 pawns etc, just panic more !!! For fail-highs I am planning to take the move without re-searching, if time is low. So I need to set it high enough, that if I get a fail high it is probably a really good move. The higher you set it, the less fail-highs you get, so it helps less. So it comes back to what is your strategy , and what are you going to do with the fail-low, fail-high situations. I only started working on this today, so I am no genius on it or anything, I am interested in other people's ideas. I am currently trying an idea of margin= max(0.1 pawns, abs( value of N-2 - value of N-1)) alpha= value of N-1 - margin beta= value of N-1 + margin So when the score is flakey and bouncing around from iteration to iteration, I use a larger bound, and when it is stable it uses a minium of 0.1 pawns. Thus I am trying to minimise my 'false alarms'.
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