Error fit: Complex value computed by model function

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data.mat

Hi I want to fit my data through the equation:

but it appears the error: Complex value computed by model function, fitting cannot continue. Try using or tightening upper and lower bounds on coefficients.

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Pietro Scapolo 2022-5-12

The equation I put in the fitting tool is:

5.*e.^(-a.*x)./(sqrt(b.^2 - a.^2)) .*(a.*sin(x.*sqrt(b.^2-a.^2))+sqrt(b.^2-a.^2).*cos(x.*sqrt(b.^2-a.^2)))

Alex Sha 2022-5-13

在 MATLAB Online 中打开

There are two parameters (a and b) only, the result will not be good:

Sum Squared Error (SSE): 779.783298373557
Root of Mean Square Error (RMSE): 0.279246002365935
Correlation Coef. (R): 0.843000031198818
R-Square: 0.710649052601208
Parameter	Best Estimate
----------	-------------
a	3714.9148653265
b	-572016.731340392