Matt, Can you explain what ifeffit does when it reads a mu(E) data file which has non-monotonically increasing energy values. Specifically what happens to data like this: # energy xmu # ---------------- 1 0.1 2 0.15 2 0.15 3 0.18 4 0.2 end so on. Ifeffit throws up one of these two sets of error messages: spline: energy data appears out of order pre_edge: energy data appears out of order or spline: energy and xmu are different length? I understand that non-monotonic data will give problems in the intepolations and elsewhere, but what does ifeffit actually do in this case? FWIW, I plan to have athena check data as it is read in to verify that the energy array is monotonic up (or down, in which case the data will be reversed) before trying to do anything with it. But I remain curious about what ifeffit chooses to do. B -- Bruce Ravel ----------------------------------- ravel@phys.washington.edu U.S. Naval Research Laboratory, Code 6134 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/