OriginLab create curve fitting

Question

I need to fit the following equation onto a plot in origin,

y = y_0 + (ka)/(((x-x_c)^2 + a^2)^(3/2))

where a is known to be 0.105, y_0 is the baseline, x_c is the peak centre. Can anyone enlighten me on how to create such a fitting function?

Thanks!

Answer 1

If the answer is still of interest:
It can be done with the nonlinar fitting tool using a user-defined function. (See Origin-Help: NLFit for an overview)
To sum up the steps:

1. Open NLFit dialog box (Ctrl + Y)
2. For function select 'new ...' and follow dialog
3. Select 'Explicit' and 'Expression', press 'Next'
4. Set y_0, ka, and x_c as parameters and add a as constant. Press 'Next'
5. Copy Function y_0 + (ka)/(((x-x_c)^2 + a^2)^(3/2)) in the function box
6. Give reasonable start values for your parameters and set the constant a to 0.105
7. In the next pages you can set limits and more, but this is optional. You can 'Finish' at this point
8. Back in the fit dialog the data should be already set, if the corresponding plot to fit was active during opening of the dialog.
9. Change to the 'parameter' tab to see the results and start the fitting with the 'fit til convergence' button to the left of the 'Fit' button
10. If it does not converge, start playing around with the start values of the parameters