How to set a parameter lower bound during curve fitting?

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Alexandria Will-Cole
评论： Alexandria Will-Cole 2018-7-25
Hello, I want to set the lower bound for my p2 variable as 0, because a negative value is unphysical for my data set.
Here is my code:
rho=Resistivityohmcm; T=TemperatureK;
plot(T,rho,'-o')
x=T; y=rho;
fnPolySq=@(p1,p2,x) p1*x.^2 + p2; %fit(x,y,fnPolySq) mask = x > 135 ; %restricts the data fit to before the upturn
f = fit(x(mask), y(mask), fnPolySq ); plot(f, T, rho)
plot(f,T,rho) disp (f)
Thanks!

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Adam Danz
Adam Danz 2018-7-25
编辑：Adam Danz 2018-7-25
Here's how you set bounds using fit()
https://www.mathworks.com/help/curvefit/fit.html#bto2vuv-1-fitOptions
See 'Lower'.
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Adam Danz
Adam Danz 2018-7-25
In the line of code you shared, I don't see where you've implemented the 'Lower' parameter. See the link again and read the section, " 'Lower' — Lower bounds on coefficients to be fitted"

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