Why do I get Cannot fit Power functions to data where X has nonpositive values when using the curve fitting tool?

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Angelavtc 2022-1-26

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https://ww2.mathworks.cn/matlabcentral/answers/1636805-why-do-i-get-cannot-fit-power-functions-to-data-where-x-has-nonpositive-values-when-using-the-curve

评论： Angelavtc 2022-1-27

采纳的回答： Matt J

myfile.mat

Dear community,

Maybe my question is obvious, but I am trying to estimate a curve with negative values for x using the "power1" type curve fitting tool. However, Matlab shows me the following error: "Cannot fit Power functions to data where X has nonpositive values".

My question is, is there a way to get rid of this error, or by mathematical construction is it impossible?

I attach my x and y values.

Thank you in advance!

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Torsten 2022-1-27

编辑：Torsten 2022-1-27

I'm not aware that a power function tends to 0 as x approaches -Inf and at the same time tends to +Inf as x approaches +Inf. So the last thing I would choose as fitting function is the power function.

I'm not sure what you mean by" function transformation". Could you clarify ?

Angelavtc 2022-1-27

@TorstenThank you very much for all your help. I understand that you mean that an exponential function is a better fit for the data. With the transformation of the function, I meant just this. The answer is clear, the parameters will be different because we fit another function. I'm sorry for the obviousness of my question. Could your comment be an answer to accept it?

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