I am trying to characterize the chi^2 merit surface for the non-linear fitting of a set of data to a sum of exponential decays:
I do this by providing a list of vaules for tau1 and fitting for everything else with NonlinearRegress, and plotting the final chi^2 value from the individual fits as a function of tau1. I've been calculating the chi^2 values with a separate statement (squaring and summing residuals) because I can't figure out how to extract the final chi^2 value from Mathematica's fit. Does anybody know how to do this? I'd like to avoid the separate statement because it slows the computation (the data set is ~12000 points long).