Nonlinear Least Squares Fitting

[Brian Gough]

Andreas Gros writes:
 >  In the section "Providing the function to be minimized" where the
 > function gsl_multifit_function_fdf is described, you mention the
 > function f that should store the distance between the values
 > calculated by the algorithm and the provided values.  As I tested
 > the algorithm I've found, that this distance is not taken as a
 > "square", instead the algebraic sign of the distance seems to be of
 > some importance. My results were quite different, whenever I took
 > (y[i]-Yi) instead of (Yi-y[i]) (as it is shown in the example).
 >  Taking the latter the solver works fine, taking the first distance
 > the results have been quite funny.

Hi,
The sign of the jacobian needs to match the sign of the function.
If you change one you need to change the other.
I think this will fix your problem.
regards
Brian