Path: news.mathworks.com!not-for-mail From: <HIDDEN> Newsgroups: comp.soft-sys.matlab Subject: Re: fit power curve with best exponent to data Date: Wed, 30 Jan 2013 19:51:08 +0000 (UTC) Organization: The MathWorks, Inc. Lines: 33 Message-ID: <kebtjc$kp3$1@newscl01ah.mathworks.com> References: <kebg5v$p8c$1@newscl01ah.mathworks.com> <kebj07$79o$1@newscl01ah.mathworks.com> <kebk50$bq1$1@newscl01ah.mathworks.com> Reply-To: <HIDDEN> NNTP-Posting-Host: www-01-blr.mathworks.com Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Trace: newscl01ah.mathworks.com 1359575468 21283 172.30.248.46 (30 Jan 2013 19:51:08 GMT) X-Complaints-To: news@mathworks.com NNTP-Posting-Date: Wed, 30 Jan 2013 19:51:08 +0000 (UTC) X-Newsreader: MATLAB Central Newsreader 3913165 Xref: news.mathworks.com comp.soft-sys.matlab:787774 "Tom Lane" <tlane@mathworks.com> wrote in message <kebk50$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(x-b)^n))') > myexp = > General model: > myexp(a,b,n,x) = exp(a*(abs(x-b)^n)) > >> fit(x,y,myexp,'start',[-20,4.47,1]) > ans = > General model: > ans(x) = exp(a*(abs(x-b)^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 'x-exponential' form where f(x) = exp[-(|z|/L)^x]. But thanks for the pointer towards 'fit'. Jack