Define a new fitting function

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Ilaria Pintus
Ilaria Pintus 2019-5-14
评论： Ilaria Pintus 2019-5-16
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
  2 个评论
Steven Lord
Steven Lord 2019-5-14
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
Ilaria Pintus 2019-5-15
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)

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采纳的回答

Steven Lord
Steven Lord 2019-5-15
Is your data stored as row vectors? If so, transpose them (using the .' operator) to be column vectors in your call to fit.

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