: Saturday, 11 April, 2009 2:25:00 AM
Subject: Re: [Ifeffit] High SO2
Scott,
I read Abhijeets's
But what I know about fitting is that we have to first fit the
first shell and then
keeping the first shell parameter constant , we go for the next shell
and Jeremy's
I typically p
Scott,
I read Abhijeets's
But what I know about fitting is that we have to first fit the
first shell and then
keeping the first shell parameter constant , we go for the next shell
and Jeremy's
I typically perform the fitting as you suggest, at least in
complicated systems, one shell at
Sorry, I wasn't trying to be provocative or confusing.
I was following up on Abhijeet's original thread, which was about
fitting a copper foil, presumably as practice for similar kinds of
materials, such as alloys. I have seen many people in workshops
proceed as he suggests with systems like
Hi Scott,
Sorry, I'm a little bit confused about what you are recommending for
and against. Earlier today you said
Well, I do know that many people do it that way, so it's not
"wrong." But there are a number of problems with it:
and
By doing that [not fitting the 1st shell with the 2nd],
On Apr 10, 2009, at 12:28 PM, Matt Newville wrote:
> In these cases, It is generally better to tell the fit to look only at
> the higher shell so that the inherent misfit in the first shell
> (inevitable, and generally of little importance to the result) does
> not dominate the total fit uncertain
Scott,
For many cases, I think it makes very little difference if you first
fit the first shell and then fit the second shell keeping "the first
shell" fixed. That is, for many cases, the two are nearly completely
separated. If they are not well separated, then you pretty much have
to fit them t
Jeremy,
I'm curious to understand this approach better. Just to confirm, as I
understand it you do something like this:
1) Fit the first shell
2) Set the first-shell parameters to their best-fit values, expand the
R-range and paths to include the second shell, and guess parameters
related t
sis using Ifeffit
Subject: Re: [Ifeffit] High SO2
Hi Abhijeet,
Well, I do know that many people do it that way, so it's not "wrong."
But there are a number of problems with it:
* You're locking in errors, rather than using additional data to
improve your fit. After all,
Hi Abhijeet,
Well, I do know that many people do it that way, so it's not "wrong."
But there are a number of problems with it:
* You're locking in errors, rather than using additional data to
improve your fit. After all, the fit to the first shell has
uncertainty, given by the error bars. B
Hello Scott Sir,
I got that ifeffit basically works on the principle
of making the theoretical data look similar to experimental data. But what
I know about fitting is that we have to first fit the first shell and then
keeping the first shell parameter constant , we go for
Hi Abhijeet,
There is no reason to fit the S02 separately for all shells. You
should use the same S02 parameter for all shells.
Ifeffit's job is to adjust the squiggly curve that comes out of the
model until it looks like the squiggly curve that comes from the data.
That's it. It doesn't kn
Hi all,
I am fitting a copper foil. I fit the first shell by using first
ss path and got it fitted nicely. Then keeping the parameters for the first
shell to be fixed , I tried to fit the second shell by taking first and
second ss but it is always coming a littel displaced and not fitting
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