On Wednesday 07 April 2004 03:24 pm, Matt Newville wrote:
What is the "three-lines trick"? It sounds like Iraida ran several different fits with kweight of 1, 2, or 3, stepping through set values for S02 ranging between 0.7 and 1.1, and fitted sigma2 (and possibly other parameters???). Is that right?
Sorry to be so dense, but what lines are supposed to cross and what is this supposed to tell you?
See page 37 (with a figure on page 38, which has a caption that I am not thrilled with on the re-reading) of http://leonardo.phys.washington.edu/~ravel/course/notes.pdf If you step through those values of S02 and fit sigma^2 at each step then make a plot, for any k-weight the plot will be close to a line. One hopes that the lines for three different k-weightings cross to form a small triangle. Presumably, that triangle is somewhere near the values for S02 and sigma^2 that you would get by floating both in a multiple k-weight fit, albeit after doing much more tedious work. B -- Bruce Ravel ----------------------------------- ravel@phys.washington.edu Code 6134, Building 3, Room 405 Naval Research Laboratory phone: (1) 202 767 2268 Washington DC 20375, USA fax: (1) 202 767 4642 NRL Synchrotron Radiation Consortium (NRL-SRC) Beamlines X11a, X11b, X23b 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/