Hello! I'm an undergraduate research student working at Boise State University. Keeping things brief, my job is to work on a project that aims to use the GNU Scientific Library to fit a large amount of data for scientific analysis.
We are using the gsl_multifit_nlinear module to fit each individual unit of data. There are three coefficients it uses that are of interest to me currently: xtol, ftol and gtol. To my knowledge, each of these are used in a separate calculation for error, each of which answer a different question about how close our current guess is to the actual data. To make things a little simpler, let's say the theoretical, ideal function for the data we are fitting is named f(x), and the function we are generating to approximate it is named g(x). - xtol roughly answers "How close are we to the original guess? Did we wander too far?" - gtol roughly answers "For every data point x, how close is f(x) to g(x)?" - ftol I'm not as certain about. I was hoping I could be provided with some insight on this coefficient. Also, I apologize if my vocabulary is a bit confusing here; as a Computer Science major, a lot of this is new to me. However, don't shy away from giving me a complex answer if that's what it takes to understand ftol, or anything about the fitter. I can decipher it with a textbook and some grit! Thank you for your time! -Spencer Fleming