[Ifeffit] data point limits in Athena?

[Bruce Ravel]

On 08/04/2013 01:49 PM, Göttlicher, Jörg wrote:
> thanks a lot for your fast reply.  I did not want to attach an
> example file immediately when submiting a question to the mailing
> list.  But there is no problem to send you some files. In the
> attachments you will now find the original data file for trying to
> reproduce my problems and hopefully to find a solution.

Jörg,

I know that it seems like you are being picked on just for asking an
innocent question and I really do apologize for any bad feelings.
However, your initial email is an example of a particularly
unproductive kind of question to ask on this (or any other) mailing
list.  While it may seem like I am being a jerk for no good reason, it
really would behoove you and *everyone* *else* reading this to think
harder about how you ask questions.

In this case, you made an incorrect assumption about the nature of the
problem.  You assumed the problem was the length of the file, when in
fact the problem was its width.  More specifically, Ifeffit and Athena
have no problems with data a few thousand data points long.  You
presumed otherwise and did not attach an example of the data that was
giving you trouble.  To reach a resolution required a snotty response
from me, a follow-up email from you, then -- finally -- useful
responses from Robert and Matt.  Had you simply attached an example of
the file giving you trouble, your problem would have been addressed
straight away and without all the attitude.

As has been explained many, many times on this mailing list, Ifeffit
(the library upon which Athena relies) is a rather old piece of
software.  It was written in an older dialect of Fortran which did not
have dynamic memory allocation.  This means that Ifeffit requests a
fixed amount of memory from the computer at start-up which cannot be
expanded upon at run-time.

The reason that the width of your file is a problem is that huge
amounts of that fixed memory are used to contain arrays that serve no
purpose to you.  Import a few of these files and **poof!** all of
Ifeffit's memory is gone.

It's either a really good thing or a really bad thing that the success
of Athena among its users is such that people feel that they can get
by without ever examining or even considering the content of their data
files.  Often that's OK.  Often it's not.

In this case, your beamline scientist isn't really doing you any favors
sending you home with such a needlessly complex data file.  Sigh....
Your best bet would be to somehow pre-process all of your data,
removing the unnecessary columns (as both Robert and Matt suggested).
This can either be done with a small, stand-along program or with a
plugin for Athena 
(http://bruceravel.github.io/demeter/aug/other/plugin.html)

B



-- 
  Bruce Ravel  ------------------------------------ bravel at bnl.gov

  National Institute of Standards and Technology
  Synchrotron Science Group at NSLS --- Beamlines U7A, X24A, X23A2
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