MATLAB: Lsqcurvefit – multiple parameters – two variables

Question

Hello,

I'm currently working on a function of two variables of the type z=f(x,y), controlled by 4 parameters, and I would like to fit data I obtained to my theoretical function. I read detailed post about how to dit with lsqcurvefit, but a problem remains. This is how I did :

function Sigma = Sigma_funct(p,Var)
Sigma = f(p(1),p(2),p(3),p(4), x,y)
end

with lets say Var(1) = x and Var(2) = y. Then, I'm supposed to use the following syntax :

    p0 = [3,1,2,10] ;
    x = lsqcurvefit(@Sigma_funct,p0,[x y],Sigma_data) ;

However, my problem is that x and y have different size, meaning that Sigma_data isn't a squared matrix : I can't concatenate x and y. How am I supposed to do ?

Thanks for your answers !

P.S : Just to say it, f is linear neither in parameters nor in variables.

Answer 1

p0 = [3,1,2,10] ;
xdata = zeros(numel(x)*numel(y),1);
ydata = reshape(Sigma_data,[numel(x)*numel(y),1]);
p_sol = lsqcurvefit(@(p,xdata)Sigma_funct(p,xdata,x,y),p0,xdata,ydata);
function Sigma = Sigma_funct(p,xdata,x,y)
Sigma_mat = f(p(1),p(2),p(3),p(4),x,y)
Sigma = reshape(Sigma_mat,[numel(x)*numel(y),1]);
end

Best wishes

Torsten.