How can I perform multivariable polynomial curve fitting?

Question

Mitchell 2013-5-15

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https://ww2.mathworks.cn/matlabcentral/answers/75890-how-can-i-perform-multivariable-polynomial-curve-fitting

评论： Abdullah Danyal Saeed 2016-11-24

Hey Community! I am looking to perform a polynomial curve fit on a set of data so that I get a multivariable polynomial. I have successfully been able to fit a variable on an independent set using polyfit(). In my case, that was "voltage as a function of current." I want to be able to perform a fit that gives me a function for something like, "voltage as a function of current and temperature." Any ideas?

Cheers!

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Abdullah Danyal Saeed 2016-11-24

Hi you can use mvregress for the above mentioned task.

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Answer 1

Shashank Prasanna 2013-5-15

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You can use the curve fitting toolbox (cftool) or the statistics toolbox (regress, LinearModel.fit, NonLinearModel.fit) to perform multiple linear regression.

If you don't have any of those toolboxes then you can set up your own optimization problem to fit your function as below:

http://www.mathworks.com/help/matlab/math/example-curve-fitting-via-optimization.html

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Mitchell 2013-5-15

So surface fitting gives me a 3D graph with x,y,z axis. From the looks of the help cftool file it seems like it is z as a function of x and y? Am I interpreting this correctly?

On another note, the temperature vector (call it y) will not be the same length as the current vector (call it x) since the experiment will be performed a discrete temperatures (say 5) and current will be ramped giving thousands of data-points. Will this be a problem?

Shashank Prasanna 2013-5-15

编辑：Shashank Prasanna 2013-5-15

1) Yes Z = f(X,Y)

2) If you don't have same size data, you may have to interpolate.

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Answer 2

cr 2013-5-15

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I dont think basic Matlab has got that ability. You will need curve fitting toolbox to do surface fitting. See this link: http://www.mathworks.in/help/curvefit/surface-fitting.html

Regards.