[Ifeffit] spline clamps in ifeffit code

Jan Stoetzel j.stoetzel at uni-wuppertal.de
Tue Dec 15 02:22:06 CST 2009


I compared the background subtracted data of my code with the data I  
got with Athena and with my code the data always looked as if the  
spline clamps did not work, since the chi(k) curve was diverging at  
the border at high k-values...
However since you said the syntax is correct I tried it again today  
with a new script and now it works fine so probably there was some  
other stupid error.

So sorry for bothering you and thanks for the answer which was very  
helpful :),


Zitat von Bruce Ravel <bravel at bnl.gov>:

> On Monday 07 December 2009 05:37:41 am you wrote:
>> Hi Bruce,
>> I have a question concerning the spline clamps in ifeffit. Is there
>> any possibility to set them directly in the spline() command? I tried
>> to do it with spline(..., clamp1=0, clamp2=24,...) but it did not work
>> and by default both spline clamps seem to be zero. Unfortunately I
>> found nothing about it in the reference guide either. So how can I
>> configure the clamps in the Ifeffit code?
>> Thanks and kind regards,
> Hi Jan,
> I am CCing this to the Ifeffit mailing list, which is the better place
> to ask a question of this sort.  I was out of town all of last week --
> had you sent this to the mailing list rather than to me directly, you
> probably would already have received an answer.
> You seem to have the syntax correct.  That is, if you follow along in
> Athena's Ifeffit buffer, you see that "spline(..., clamp1=0,
> clamp2=24,...)" is exactly what she does.  Anything you see in the
> Ifeffit buffer should be directly transplantable to an Ifeffit
> script.  Indeed, that is the very purpose of making the Ifeffit buffer
> available to the user.
> So, what do you mean that the clamps both seem to be zero?  How do you
> know that?  Can you show us an example data file and a short example
> ifeffit script that demonstrates the problem?  It is quite possible
> that changing the clamp strength will have no significant impact of
> the background removal.  To refresh my memory as I am writing this
> email, I loaded an iron foil spectrum into Athena.  Indeed, changing
> clamp 2 has little impact on the background removal.  But I know from
> experience that, in general, it does.
> Just to tell the whole story, I'll point out that the numeric values
> of the clamp strengths in Athena are configurable.  If you go to Edit
> preferences, then open the clamp group, you will be able to assign new
> values to the 5 named clamp strengths.
> HTH,
> B
> --
>  Bruce Ravel  ------------------------------------ bravel at bnl.gov
>  National Institute of Standards and Technology
>  Synchrotron Methods Group at NSLS --- Beamlines U7A, X24A, X23A2
>  Building 535A
>  Upton NY, 11973
>  My homepage:    http://xafs.org/BruceRavel
>  EXAFS software: http://cars9.uchicago.edu/~ravel/software/exafs/

Dipl.-Phys. Jan Stötzel
Fachbereich C / Physik, Bergische Universität Wuppertal
Gaußstr. 20, D-42097 Wuppertal, Germany

E-mail: j.stoetzel at uni-wuppertal.de
phone: +49 202 439-3105, fax: -3101, secretary: -3102

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