[Ifeffit] RE: Plots of apodization Windows in Athena 0.8.005 and artemis.0. 5.004

SCHLEGEL Michel 177447 schlegel at azurite.cea.fr
Tue Jan 7 05:06:17 CST 2003


Hello,

> I hope you don't mind that I am sending my responses to your questions
> to the Ifeffit mailing list.  They seem of sufficiently general
> interest that I think the Ifeffit list would be interested.

I don't. :)
 

>  MS> Another detail which kind of puzzles me: whenewever I use a
>  MS> Kaiser-Bessel window and increase the weight, the *plotted*
>  MS> limits of the apodization window shift away from the positions
>  MS> defined in the command window (e.g., for positions set to 2 and
>  MS> 13 Å-1 in the command window and a weight dk = 1, the plotted
>  MS> apodization limits are shifted to 1 and 14 Å-1).
> 
> I am a bit confused by the numbers you give in that they are not
> consistent with what I observe when I make a plot displaying a
> Kaiser-Bessel window.  Here is what I observe:

> 
>   For a window defined by kmin=2, kmax=18, and dk=2, the first
>   non-zero value of the window is at k=1 and the last non-zero value
>   is at k=19.  In general terms, the first non-zero value of the
>   Kaiser-Bessel window is at kmin-dk/2 and the last is at kmax+dk/2.

OK, I wanted to make the distinction between the first and last non-zero
values as they *appear* in the graphic window, and the numerical values as
stored as internal values in the software. I assumed that these values were
not the same. This assumption, but was -partly - justified by the wollowing
reason: If I keep kmin and kmax constant and increase dk, I increase the
k-range covered by the K.B. window, and this should result in an increase of
the number of independent points. What I observe is that the number of
independent points calculated by artemis is *not* affected by dk, suggesting
that the FT range remains limite to [kmin, kmax]. 


> The bottom line is that you may want to set kmin a bit higher so that
> kmin-dk/2 is at the point where you want the window to start.  Note
> that setting dk to 0 is probably *not* what you want to do, although
> it is probably worth doing so just once to see what happens to the K-B
> window.

I did: the first and last non-zero values plot exactly at kmin and kmax. 

>  MS> A final 'cosmetic' suggestion: would it be possible in future
>  MS> versions of artemis, to plot both the amplitude and real part, or
>  MS> amplitude and imaginary parts of experimental and simulated
>  MS> chi(R) together?
> 
> 
> You are not the first person to ask for this, Michel, but the last
> time this came up, Artemis was much less far along.  

Sorry for being late...

> So, let me put it up to discussion among the folk on this mailing
> list.  What should Artemis do?
> 
>   1.  Allow the user to select one or more parts of chi(R) (or chi(q)
>       for that matter) and plot each of those parts for each of the
>       things selected in the "Paths" list.
>   2.  Allow the user to somehow specify which parts of chi(R) to plot
>       for the data, the fit, and each path individually.  (This would
>       make the interface somewhat more complex.)
>   3.  Continue to work exactly as it works now.
>   4.  Something else entirely.

Basically in a simulation, both the amplitude and the phase of selected
paths may be (shoud be?) compared.  Therefore, I would select (1) (but let
me reiterate that this is not a priority to me). 

Thanks in advance, and happy new year,

Michel Schlegel 



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