[Ifeffit] path-sensitive math expressions

Bruce Ravel ravel at phys.washington.edu
Fri Sep 5 13:13:44 CDT 2003

Hi Matt,

I have some questions about a subtle detail in ifeffit.  It is
possible to make a def parameter which is path sensitive in the sense
that it will evaluate differently for different paths.  Any def
parameter which includes reff, eins(), or debye() in its math
expression will be that way.

Here is a simple, if slightly silly, example:
   def  rrr = reff/10
   path(1, feff=feff0001.dat, dr=rrr)
   path(2, feff=feff0002.dat, dr=rrr)
   show rrr
will report 1/10 the R_eff of the *second* path.
So here are my questions:

1.  Are all def parameters reevaluated every time a new path is
    evaluated?  Or only if the path uses the def parameter in one of
    its math expressions?  (I think the answer is the former.)

2.  Is it possible to ask ifeffit which def parameters are path
    sensitive?  Of course, I can scan the def parameters at the level
    of perl to see if any of them obviously are, but ifeffit might
    already know that.

3.  If you do
       show ss
    the value is the value of the last path evaluated.  Doing
       show @path N
       show ss
    will indeed display the value of the def parameter appropriate to
    the Nth path.  Is there another way of forcing ss to be evaluated
    appropriate to a desired path?

 Bruce Ravel  ----------------------------------- ravel at 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/

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