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problem with nonlinear fit
Hi everybody, I have to fit the function e = (s/K)^(Na)*(t/a)^a (s = constant; t = variable; K,N,a = parameters) to a given set of datas. Then, I have used the NonlinearFit function (Statistics'NonlinearFit' package), but I have two problems: 1) I can't specify any start values or range using. I tried to give them as any forms, but I always got error messages concerning these parameters. 2) mathematica shows kind of a strange behavior when repeating the fit operation, sometimes it keeps old values and sometimes it reports different error messages. Any help welcome, Thanks in advance, Dragan.