MATLAB: Options when drawing using the Curve Fitting tool

curve fitting toolnonlinear regression graph

I am inputting x y z data and using 'Curve Fitting tool' to create a nonlinear regression graph.

I am trying to find the coefficients a,b,c,d suitable for the data using the 'Custom Equation' formula, but the graph is too different from the data.

I tried changing Robust and Algorithm, but the graph is not similar to the data.

What additional work should I do to get the graph?

Best Answer

Hi, post your data and function in txt format, if possible.

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MATLAB: Options when drawing using the Curve Fitting tool

Your datapoints seem to have a polynomial relationship, not logarithmic. I think your should change your model. In addition, visual check is not enough for curve fitting. There are lots of things to check after fitting the model in order to reach a good model. Please read:

https://www.mathworks.com/help/curvefit/curve-fitting.html

Especially fit potsprocessing > residual analysis.

MATLAB: How to fit a custom equation

I get good results with this:

yf = @(b,x) b(1).*(1-exp(-b(2)*(b(3)+x)));
B0 = [5000; 0.01; 10];
[Bm,normresm] = fminsearch(@(b) norm(y - yf(b,x)), B0);
SSE = sum((y - yf(Bm,x)).^2)
Bm =
          6677.76372320411
        0.0084077646869843
          47.1622210493944
normresm =
          195.173589996072
SSE =
          38092.7302319547

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MATLAB: Options when drawing using the Curve Fitting tool

MATLAB: How to fit a custom equation

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