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Best fit curve for non-linear data with 3 unknowns

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Shaunak Chandwadkar
回答： Alan Weiss 2017-3-8
Hello, I am trying to fit a curve on my experimental data. (.mat file attached) I am using only the time and and load data (column 1 and 5 respectively) The equation I need to curve fit is
load=(((8*sqrt(R)*((k)^(3/2))*(sqrt(tR1))*E1)./(2*((E1+E2)^2))).*((E2*(E1+E2).*tR1)-(((E1.*eta*(exp(-(E1+E2).*t./eta)))*((-exp((E1+E2)*tR1/eta))+1)))));
where the known variables are
R=2.5e-3;
k=2.5E-06;
tR=130.37; (first time step)
t= first column of data.mat (time step or instantaneous time)
Unknows are E1, E2 and ETA in the equation.
Starting values:
E1in=2.000000e+04
E2in=4.000000e+04
etain=1.000000e+05
How can I use Fmincon or nlinfit or some more appropriate function to fit the data and get the required E1, E2 and Eta?

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Alan Weiss
Alan Weiss 2017-3-8
Perhaps this example will help.
Alan Weiss
MATLAB mathematical toolbox documentation

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