lorenz

This is a lorenzian function of the form:

f (x) = $\displaystyle {\frac{{a_2 a_1}}{{4(x-a_0)^2 + a_1}}}$.

I chose not to use the usual form, because I thought making the form simple in regards to the parameters might make for more robust fitting. You have to think to eyeball the initial paremeters though. If your data is a lorenzian, it will converge without much trouble. If your data is not really a lorenzian you may have trouble. The gaussian is a better choice to fit peaks that are not well characterized by a particular function.