Options when drawing using the Curve Fitting tool

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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?

Accepted Answer

Alex Sha
Alex Sha on 23 Aug 2020
Hi, post your data and function in txt format, if possible.
Alex Sha
Alex Sha on 24 Aug 2020
The fitting result is not so good if the function is: z=a*x+b*log10(y+c)
Root of Mean Square Error (RMSE): 0.115584191368428
Sum of Squared Residual: 0.654625559420376
Correlation Coef. (R): 0.855538827407886
R-Square: 0.731946685202461
Adjusted R-Square: 0.714076464215958
Parameter Best Estimate
---------- -------------
a 0.0741121571659251
b -0.283418916981476
c -9.47213514559854

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