Uncertainty in Exponential Decay Fitting?

Hi All,

I am fitting a set of data to an exponential decay curve using the fitnlm() function. The results are nice, the data clearly represents exponential decay and the algorithm works. The formula is y(x) = ae^(-bx) + c. I need uncertainties on a, b, and c, and in particular b (the one I really care about. I can't seem to find a good formula for this – does anyone have a suggestion?

Furthermore, is there a Matlab function that will do this for me?

Thank you!