How to fit data with an arbitrary lorentzian function

I created a function:

x0=1960

y=10

x=linspace(x0-100,x0+100,200)

F=(1/pi*y)*(y^2./(x-x0).^2+y^2)

plot(x,F,'LineWidth',1)

PlotLorentzian = [x', F']; % compile into data format

writematrix(PlotLorentzian,'plotlorentzian.m','filetype','text')

Now I want to fit data from OneLorentzian.txt to this function. OneLorentzian.txt has x in the first column and the output is F; the values of x0 and y are different than the values in the above function but the equation is the same. I need to write a code to fit this spectrum to the function I made, and determine the x0 and y values. The data has a Lorentzian curve shape.

data=load('OneLorentzian.txt')

fitx=data(:,1)

L=data(:,2)

plot(fitx,L)

Lorentzian=fittype(@(fitx,fity)(1/pi*fity)*(fity^2./(fitx-x02).^2+fity^2))

The last line of code isn't working and I'm stuck. Any help is appreciated.

Answer 1

[Keerthana Chiruvolu]

Hi,

The error in last line of code can be eliminated by,

• Specifying the independent parameters in the function
• Proper use dot operator( .^, .*)
• Identifying any missing operators in x02. In case x02 is a variable, check if its defined in the code or MATLAB Workspace

Sample code:

Lorentzian=fittype(@(fitx,fity)(1/pi*fity).*(fity.^2./(fitx-x0*2).^2+fity.^2),'independent','fity')

Please refer the link for more information on creating fittypes with Anonymous functions.