1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Lorenzian and gaussian pdf-function fitting with Matlabs nlinfit, confidence interval

  1. Nov 27, 2009 #1
    I have data that I want to fit to both Gaussian and Lorentzian (Cauchy) distribution. I have been using Matlab's nlinfit as follows:

    gaus = @(p,xdata) (p(1)/(sqrt(2*pi*p(2)))*exp(-(xdata-p(3)).^2/(2*p(2)))+min).*weights;
    [g_pfit,g_residual,g_J]=nlinfit(data(:,1), data(:,2).*weights, gaus, [4030 2 -5]);

    loren = @(p,xdata) p(1)./(pi*p(2)*(1+((xdata-p(3))./p(2)).^2))+p(4);
    [l_pfit,l_residual,l_J]=nlinfit(data(:,1), data(:,2), loren, [10030 0.5 -5 4]);

    The strange thing, however, is that my data is more like Gaussian-shaped and Gaussian curve, is by eye way more better fit. Still I get smaller errors for the width of Lorentzian fit than Gaussian (using the nlparci function).

    Why would I get smaller errors for the width of the Lorentzian curve than for the width of the Gaussian curve, which is a better fit?

  2. jcsd
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Can you offer guidance or do you also need help?
Draft saved Draft deleted