[Ifeffit] Asymmetric error bars in IFeffit

[Scott Calvin]

Yes; it's a case of trying to distinguish between a few boulders and  
lots of pebbles; the total volume isn't the issue.

What I'm looking at is something like surface/volume ratio, but with  
"surface" being path-dependent and gradual. For a nearest-neighbor  
path, only the top monolayer of atoms are on the surface. For a 5  
angstrom path, the transition region from "surface" to "core" extends  
5 angstroms in.

But that more sophisticated definition of "surface" doesn't change the  
fact that the dominant dependence is 1/R, so that should address the  
issue.

--Scott Calvin
Sarah Lawrence College

On Oct 25, 2010, at 4:43 AM, Matt Newville wrote:

> Hi Scott,
>
> That's a pretty amazing use case.
>
> But I'm not sure I understand the issue exactly right.   I would have
> thought the volume (r**3) was the important physical parameter, and
> that a 1000nm particle would dominate the spectra over 3nm particles.
>   Or is it that you are trying to distinguish between 1 very large
> crystal  or 100s of smaller crystals?   Perhaps the effect you're
> really trying to account for is the surface/volume ratio?  If so, I
> think using Matthew Marcus's suggestion of using 1/r (with a safety
> margin) makes the most sense.
>
> --Matt
>