Error in fitting two parameters with lsqnonlin

Question

Cynthia Struijk 2019-9-18

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https://ww2.mathworks.cn/matlabcentral/answers/480977-error-in-fitting-two-parameters-with-lsqnonlin

编辑： Cynthia Struijk 2019-9-20

I want to fit two parameters using lsqnonlin. I have set up my system of ODE and want to solve them with my new parameters that are found after I performed the lsqnonlin.

I think the problem has to do with the fact that my parameters are in parameter struct par and that I don't want to fit on all of these parameters, but just on basis of two of those.

This is my main script for performing the curve fitting % initial guesses for model parameters, no. of indeces is number of fitted % parameters k0 = [0.028 0.002];

Note that I want to fit for par.kb and par.kf

The error I get is:

I know my initial guesses are close enough. Does anyone know what my problem is?

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Answer 1

Matt J 2019-9-18

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https://ww2.mathworks.cn/matlabcentral/answers/480977-error-in-fitting-two-parameters-with-lsqnonlin#answer_392467

[curve_fit_parameters,RESNORM,RESIDUAL,EXITFLAG,OUTPUT,LAMBDA,JACOBIAN] = 
...
lsqnonlin(@(k) fitcrit(k,time_exp, conc_exp, par, init),k0,LB,UB,options)

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Cynthia Struijk 2019-9-18

Thank you very much, I do not get any errors anymore. However, the outcoming fitted parameters seem to be my initial guessed values, but I will try to fix this myself first!

Bjorn Gustavsson 2019-9-18

In addition it seems the ODE-function in the ode45-call needs to be modified to something like:

[time_model_fit,conc_model_fit] = ode45(@(t,c) CSTRSinSeries(t,c,par),time_exp,init, 
[]);

The call-sequence used was the old-style method of sending in additional parameters, but since it is not to be found in the documentation (as far as I could see) it is a functionality that Mathworks might remove arbitrarily soon.

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