Author: James Swafford
Date: 04:29:39 10/22/01
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On October 22, 2001 at 06:24:45, Rémi Coulom wrote: >On October 21, 2001 at 07:06:41, James Swafford wrote: > >>On October 21, 2001 at 02:37:09, Rémi Coulom wrote: >> >>>On October 21, 2001 at 00:11:23, James Swafford wrote: >>> >>>If your evaluation function is, say, f(w_1, w_2, ..., w_n), then the partial >>>derivative of f with respect to weight w_i is the limit of >>>(f(w_1, ..., w_i + epsilon, ..., wn) - f(w_1, ..., w_i, ..., w_n)) / epsilon >>>when epsilon goes to zero. In practice, you can estimate this value by measuring >>>the ratio above with a very small value of epsilon. >> >> >>That is starting to make sense, but I'll have to sit down and think >>about it later today. What is a reasonable value for epsilon? >> > >If your function and weights are integers, this is a not easy to make a good >choice. Maybe epsilon = 1 or epsilon = 2 would work. The trick is that epsilon >should be large enough so that changing w_i to w_i + epsilon changes the >evaluation function if the derivative is not zero. > >I have not implemented TD(lambda) for my own chess program yet, but I suppose I >would make a floating point evaluation function in that case. With a floating >point evaluation, things are much easier. For instance, taking epsilon to be >1/1000 of the typical weight value should work nicely. An optimal value for >epsilon could be found, but this really is no big deal. Accuracy is not >important at all. > >Remi > Thank you Remi... this helps quite a lot. -- James >Remi
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