[Ifeffit] Athena normalization and deglitching bugs

[Bruce Ravel]

On Saturday 29 May 2004 02:43 pm, Scott Calvin wrote:
SC> First of all, on any file, including the copper data that comes with
SC> Athena, there is a bug. To see it, go to the deglitch screen, and
SC> change Emax by picking a point off the plot. Then replot. From now
SC> on, the green "tolerance" lines extend from Emax up to the end of the
SC> plot, rather than from Emin to Emax. This seems to affect only the
SC> screen display (i.e. it still deglitches the intended range), but it
SC> does make it harder to see what will get deglitched.

OK.  I'll look into this and put it on the to do list.  

SC> In the project I am giving you, the data is very glitchy (lots of
SC> Bragg peaks). Go down to the group labeled SBT/B Bi LIII Merge and
SC> plot in E-space with the post-edge line. Does it look right to you?
SC> It looks like the normalization line is considerably higher than it
SC> should be given the normalization range chosen, with only a few
SC> glitches above it. Is that something I don't understand about the way
SC> the post-edge line is chosen, or is it displaying the line wrong, or
SC> is it calculating it wrong?

I looked at your data and I don't believe anything is wrong.  The data
after the big white line is somewhat concave downward, thus you would
expect the post edge line to be similarly concave downward.  However,
you chose a value for the lower end of the normalization range that
was well up into the white line.  Having a fairly large number of
points in the normalization range and in the white line biased the
regression (and it IS a regression and not a fit) such that the post
edge line was, as you say, "above the data".  When I chose a lower end
of the normalization range that was completely beyond the white line,
the post edge line went right through the data as expected.

B

-- 
 Bruce Ravel  ----------------------------------- ravel at phys.washington.edu
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