MATLAB: Least Square Minimization (Levenberg-Marquant method) of damped oscillation curves

damped oscillationsleast square minimzationMATLAB and Simulink Student Suite

Hi,

My goal is to fit my experimental data (attached) with the following equation with Levenberg Marquant method :

A*exp(-c*t)*sin(2*pi*f*t+phi), where A is the amplitude, t is time, c is the damping coefficient and f the frequency and phi the phase coefficient.

As my skills are weak in least square minimzation in Matlab, thanks in advance for your help,

Louise.

Best Answer

You can use lsqcurvefit with the 'levenberg-marquardt' Algorithm setting

https://www.mathworks.com/help/optim/ug/lsqcurvefit.html#buuhcjo-options

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MATLAB: I get matlab error :Failure in initial user-supplied objective function evaluation. FMINCON cannot continue.

1. Input vector for the objective function F is only x, not x and xdata.
2. I don't see that you define "xdata".
3. Since I suspect that "xdata" will be a vector, take care that F returns a scalar. As it stands, F returns a vector.

Best wishes

Torsten.

MATLAB: Lsqcurvefit nonlinear model: experimental data with model prediction

how can i fit two data simultaneously (same xdata but different ydata, for each ydata same function but i just want to change the value "80").

Just concatenate the data together and write a bigger model function with more variables that describes both.

https://www.mathworks.com/matlabcentral/answers/431697-make-curve-fitting-faster

For a small number of fits, however, it's usually not worthwhile.

How can I get a better fit

I find that fitting the log of the data gives better results,

[x] =  lsqcurvefit(@(p,xd)log(fun(p,xd)),x0,xdata,log(ydata),lb,ub,options);

Best Answer

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MATLAB: I get matlab error :Failure in initial user-supplied objective function evaluation. FMINCON cannot continue.

MATLAB: Lsqcurvefit nonlinear model: experimental data with model prediction

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