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Error fit: Complex value computed by model function

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Pietro Scapolo
Pietro Scapolo 2022-5-12
评论： Alex Sha 2022-5-13
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
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
Alex Sha 2022-5-13
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

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回答（1 个）

Torsten
Torsten 2022-5-12
编辑：Torsten 2022-5-12
Fit under the constraint
b^2-a^2 >= 0

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