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JK
Posts:
6
Registered:
12/9/12


Re: fit power curve with best exponent to data
Posted:
Jan 30, 2013 2:51 PM


"Tom Lane" <tlane@mathworks.com> wrote in message <kebk50$bq1$1@newscl01ah.mathworks.com>... > >> I'm attempting to fit the following equation to a set of data > >> characterizing something's autocorrelation function: > >> > >> y=e^(a*x)^n > > Your y seems to drop off exponentially, so you want the exponent to be > negative, and you're raising it to a power that may not be an integer. If I > change your function I can do the following to fit it: > > >> myexp = fittype('exp(a*(abs(xb)^n))') > myexp = > General model: > myexp(a,b,n,x) = exp(a*(abs(xb)^n)) > >> fit(x,y,myexp,'start',[20,4.47,1]) > ans = > General model: > ans(x) = exp(a*(abs(xb)^n)) > Coefficients (with 95% confidence bounds): > a = 103.6 (115.1, 92.15) > b = 4.475 (4.474, 4.475) > n = 1.065 (1.035, 1.094) > > While you may not want this function, I hope this illustrates what you can > try with a function that you choose yourself. > >  Tom
Hi Tom,
Yeah that's exactly what I was looking for, I'm just having trouble getting one type of model to work: an 'xexponential' form where f(x) = exp[(z/L)^x]. But thanks for the pointer towards 'fit'.
Jack



