Define a new fitting function

Hello everyone!

I need to define a new fitting function that is not in the matlab library. I've already tried to use the "fit App" but then I wasn't able to save the function and so re-use it. Now I'm trying in this way but it doesn't work.

model_1 = fittype('a*netOD_red+b*(netOD_red)^3','independent','netOD_red','dependent','dose')

fit_model_1 = fit(netOD_red, dose, model_1)

where my X vector is "netOD_red" and my Y vector is "dose".

The function I want to use is Y= a*X+b*(X)^3

Can someone help me? Thank you

[Steven Lord]

Can you clarify what "it doesn't work" means?

Does MATLAB throw an error? If so what is the full and exact text of the error message you receive -- all the text displayed in red?

Does MATLAB issue a warning? If so what is the full and exact text of the warning message you receive -- all the text displayed in orange?

Does MATLAB give you a different result than you expected? If so can you show us a (small) data set and the code you use to obtain the answer (the code in your original message only shows how you created the fit -- show us how you used that fit to get the numeric result) and explain what you expected?

This information may help us understand what went wrong and/or what you're trying to do.

[Ilaria Pintus]

This is what I obtain in the Command Window:

model_1 =

General model:

model_1(a,b,netOD_red) = a*netOD_red+b*(netOD_red)^3

Error using fit>iFit (line 135)

X must be a matrix with one or two

columns.

Error in fit (line 116)

[fitobj, goodness, output, convmsg]

= iFit( xdatain, ydatain,

fittypeobj, ...

Error in ALL (line 442)

fit_model_1 = fit(netOD_red, dose,

model_1)

Answer 1

[Steven Lord]

Is your data stored as row vectors? If so, transpose them (using the .' operator) to be column vectors in your call to fit.

[Ilaria Pintus]

Thank you so much!