lorentzian fit

In the attached file example i use "nlinfit", which can fit any kind of function that you want. the

Description

On the gaussian fit i used "polyfit" which gives you en absolut one solution, but have some problems fitting non-linear model.

In the attached file example i use "nlinfit", which can fit any kind of function that you want. the problem is that you need to give here a starting point.

"main.m" include the example code to use nlinfit.

"data.txt" is data (x,y) that needed to be fitted.

"fun.m" is the function to be fitted, in you case it's lorentzian.

• MATLAB release: MATLAB 7 (R14)
• Other requirements: the function "nlinfit"

[victor yashunsky]

 

[Oliver Chen]

This was very helpful in my understanding of the gaussian fit. thank you

[Arye Lerner]

Exellent. Thanks.

[ander zornoza]

when I introduce my data an error ocurs:

??? Error using ==> nlinfit at 129
MODELFUN should return a vector of fitted values the same length as Y.

Error in ==> main at 56
vEnd=nlinfit(x,yOrig,@fun,vStart);

Please I need Help

[Patrick Ledingham]

Excellent. Works really well. Thanks

[Chad Bircher]

When I attempt to use these programs I get the following error
Undefined function or method 'nlinfit' for input arguments of type
'function_handle'.
 Do you know why MatLab would respond to the programs this way?

[Eric Zilli]

Not terribly useful. This is an example, not a fitting function and it is not very well written. It is, however, slightly more useful than the poor documentation on the function nlinfit.

The code does not seem to be performing a fit to a Lorentzian, though, as the function fun.m (why not give it a more useful name?) is multiplied by 2 for some reason and the (x-x_0) term in the denominator is multiplied by 4 for some reason. Possibly this is a standard form in some field I have never come across, but this is certainly not the Lorentzian function I am interested in fitting. It is easy enough to fix, but worth pointing out to others who might use this.

[sohag khan]

your code don't work to fit my data in Lorentzian. Can u please help?
here is my data

a=[-1000*1e3 -100*1e3 -10*1e3 -5*1e3 -1*1e3 0 1*1e3 5*1e3 10*1e3 100*1e3 1000*1e3];
b=[-110 -90 -80 -70 -60 0 -60 -70 -80 -90 -110];
data in b is in dB
can u plz help me to find the fit.
thanks

Reza

[guo]

good