[Ifeffit] Question with FL Database

Matt Newville newville at cars.uchicago.edu
Tue Nov 8 10:14:39 CST 2005


Marco,

> A while ago I wrote asking about how to read the Farrel Lytle Database and I 
> get a pretty nice reply of Matt with the Ifeffit FAQ on "How to read the 
> Farrel Lytle database" :P (I forgot to read that before asking!!)
> However the FL database have several file headers, like the following; 
> 
> CUEDGE START STOP BEG FSCTS:  168620.  176900.  142200.    2000.       5.
>  DELTA:     200.      10.      40.      80.       0.
> DELEND:  169600.  167600.  159300.  142200.       0.
>    SEC:       1.       1.       2.       3.       1. 
> 
> I figure that the values first line values are still motor steps, but is 
> there a sort of "known" dspace and step/deg value for these cases?. Maybe 
> I'm in other edge?

Yes, there are a few different formats of data in the Lytle
database. As far as I can tell, the files with 
'CUEDGE START STOP BEG FSCTS: ...' 

do not include a "known"  d-spacing or steps-per-degree, but
tend to use Si(111) (dspace = 1.9202).   You didn't include the 
rest of the file or say which file you're trying to use, so it's 
impossible to tell what problem you're having.  

Many of the files like this in the Lytle database also have data
layed out in a fairly strange way, with steps,mu in pairs but 4
to a line.  These have to be read with a 'narrays=2' argument to
read_data(). Such files can usually be read with this macro:

# read Farrel Lytle data file, convert to mu(E)
macro read_lytle file group 4000
  " Read some Lytle datafiles : filename groupname steps-per-degree"
  read_data ($1, group=$2, narrays=2)
  set (dspace  = 1.92017,     stpdeg  = $3)
  set (r2d     = 57.29577951, hc      = 12398.61)
  set $2.energy =  hc / (2 * dspace) / sin($2.1 / (r2d * stpdeg))
  set $2.xmu    = $2.2
end macro

with 'steps-per-degree' usually either 4000, 8000, or 16000, and 
used as in:

Ifeffit> read_lytle cuzno.012 cuzno 8000

You may have to play with it some.

If that doesn't help, please ask a more specific question.

--Matt




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