[Ifeffit] minimize function

On Tue, 28 Jan 2003, "Kelly, Shelly D." said:

SDK> Hi, I would like to use the minimize function to fit a line to SDK> some data points. I could not find documentation on the SDK> r-square factor that is referred to as the confidence level for SDK> the fit. I was just browsing through `iff_minimize.f'. I am sure that Matt will correct me if I am wrong, but it seems as though no R-factor is evaluated by a call to minimize() in ifeffit. Chi-square is essentially the sum of squares of the function that you minimize (which, in your case, presumably, is the data minus the line). It and a reduced chi-square (normalized by the number of points in the minimization function minus the number of variables) are evaluated and stored as program variables, but there appears to be no R-factor that is stored. I just did a minimize and that seems to be the case, despite what it says in chapter 7 of the Ifeffit tutorial on Matt's website. If you were to make an R-factor that is the real-array equivalent of Ifeffit computes when fitting (imaginary) R-space EXAFS data, it would be something like: Npts [function(i) - data(i)]^2 R = sum ---------------------------- i=i data(i)^2 That would be a sort of positive-definate, percentage misfit and would be trivial to compute using ifeffit's array manipulation. HTH, B -- Bruce Ravel ----------------------------------- ravel@phys.washington.edu Code 6134, Building 3, Room 222 Naval Research Laboratory phone: (1) 202 767 5947 Washington DC 20375, USA fax: (1) 202 767 1697 NRL Synchrotron Radiation Consortium (NRL-SRC) Beamlines X11a, X11b, X23b, X24c, U4b National Synchrotron Light Source Brookhaven National Laboratory, Upton, NY 11973 My homepage: http://feff.phys.washington.edu/~ravel EXAFS software: http://feff.phys.washington.edu/~ravel/software/exafs/