[Ifeffit] Re: from I.Demchenko ...

[Bruce Ravel]

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


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