Hi all, This is a continuation of the discussion from help-gsl on computing the R^2 "coefficient of determination" for multi-parameter fits. I think it would be a useful thing to have and I propose that the best way to add it in would be to compute it in gsl_multifit_linear and gsl_multifit_wlinear and store it in the gsl_multifit workspace. Then provide a function like gsl_multifit_linear_Rsq to return the value to the user. This way we wouldn't need to change the api and the multifit_linear routines would remain backwards compatible.
Computing the value would require adding about 4-5 lines of code and it can be computed at the same time as chisq so there doesn't have to be an extra loop added in. Patrick Alken
