[Ifeffit] Another R-factor question

[Wayne Lukens]

Hi Matt,

Thanks again for clearing up my confusion over the origin of the R 
factor for
fits in R-space.  I now have a different and unrelated question about 
the R factor.
 From looking through the ifeffit code, it appears that the R factor is 
defined as
sum(data-fit)/sum(data).  Is this correct?

The reason that I am asking is that I would like to use Hamilton's test 
(Acta Cryst 1965, V18, p.502)
to determine whether adding additional shells to a fit actually results 
in
a better fit.  Hamilton's test uses the "crystallographic R factor", 
which is
sqrt(sum(data-fit)/sum(data)), so I would like to know whether or not 
to take
the square root of the R-factor ratios in Hamilton's test.  Thanks 
again for
the help!

Sincerely,

Wayne

---
Wayne Lukens
Scientist
Lawrence Berkeley National Laboratory
email: wwlukens at lbl.gov
phone: (510) 486-4305
FAX: (510) 486-5596