Question

I’m trying to do some fitting with lsqcurvefit. I have a function like that:

function F = cdf_3p_model(a,data)
F=1-((1-a(5)-a(6)).*(exp(-abs(data)./a(1)))+((1-a(4)-a(6)).*(exp(-abs(data)./a(2))))+((1-a(4)-a(5)).*(exp(-abs(data)./a(3)))));

and

function [a residual] = cdf_fit_3p(x,y)
a0 = [10 1 0.1 0.3 0.3 0.3];
lb = [0 0 0 0 0 0];
ub = [];
curvefitoptions = optimset('Display','final','MaxFunEvals',100000,'MaxIter',50000);
[a, residual] = fmincon(@cdf_3p_model,a0,x,y,lb,ub,curvefitoptions);
end

I set the initial parameters, ub, lb but how do I also declare that:

a(1) > a(2) > a(3)
a(5) + a(6) +a(7) = 1

Answer 1

I think you have better chance using one of the minimization routines such as fmincon which allows you to specify constraints you might otherwise be unable to do. You can easily incorporate least-squares by taking the L2-norm of the difference between model and data