How to fit a set of curves where each curve depends on the value of one parameter?

Hi, guys!

I have the following function:

 y_m(i,:) = coeff_0*(1 - w_m(i))*x_m(i,:).*exp(abs(x_m(i,:)).^(1/2));

with 2 parameters ("coeff_0" and "w_m"). For a set of "x_m" measured data I get a set of "y_m" data, resulting in a set of curves. "coeff_0" is fixed but I need to calculate it. "w_m" must be calculated for each "i" curve. I tried to use the "nlmefit" function but the following error is prompted: "After the initial refinement of the fixed effects with the Levenberg-Marquardt algorithm the Jacobian at BETA0 is ill-conditioned. Some fixed effects may not be identifiable resulting in a poor estimation. Check for possible aliased parameters of your model, or try setting 'RefineBeta0' to FALSE."

Do you have some suggestion for me? Is there any better function to fit the curves?

Thanks in advance!

Luiz Alberto

[dpb]

Have you done the first step of plotting your data to see if it really looks like anything?