Best fit curve for non-linear data with 3 unknowns

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?

Answer 1

[Alan Weiss]

Perhaps this example will help.

Alan Weiss

MATLAB mathematical toolbox documentation