Re: [Ifeffit] General question

[Dimitar Popmintchev]

Thank you!

Dimitar

On Fri, Oct 14, 2016 at 6:54 AM, Bruce Ravel  wrote:

> On 10/13/2016 05:17 PM, Dimitar Popmintchev wrote:
>
>> I would like to ask, after a fit (in Artemis) which column in the output
>> file gives the uncertainty for peaks position dR (R+/-dR  i.e. 3+/-0.02
>> Angstroms)  ?
>>
>
> Error bars are not propagated in Artemis currently.  That's something you,
> the user, has to do using the math expression that relates your variable(s)
> to the delta R in question.
>
> The simplest common case is one where you have
>
>guess delr = 0
>
> then later, for some path,
>
>reff   = 3.0
>deltaR = delr
>
> In that case, delr is varied and the path length is 3.0 + delr.
>
> Propagating the uncertainty in this case is trivial:
>
>delta( 3.0 + delr) = delta(3.0) + delta(delr)
>
> 3.0 is a constant, so the error bar in the path length is the same as the
> error bar in the variable.
>
> HTH,
> B
>
>
>
> --
>  Bruce Ravel   bra...@bnl.gov
>
>  National Institute of Standards and Technology
>  Synchrotron Science Group at NSLS-II
>  Building 743, Room 114
>  Upton NY, 11973
>
>  Homepage:http://bruceravel.github.io/home/
>  Software:https://github.com/bruceravel
>  Demeter: http://bruceravel.github.io/demeter/
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Re: [Ifeffit] General question

[Bruce Ravel]

On 10/13/2016 05:17 PM, Dimitar Popmintchev wrote:

I would like to ask, after a fit (in Artemis) which column in the output
file gives the uncertainty for peaks position dR (R+/-dR  i.e. 3+/-0.02
Angstroms)  ?


Error bars are not propagated in Artemis currently.  That's something 
you, the user, has to do using the math expression that relates your 
variable(s) to the delta R in question.


The simplest common case is one where you have

   guess delr = 0

then later, for some path,

   reff   = 3.0
   deltaR = delr

In that case, delr is varied and the path length is 3.0 + delr.

Propagating the uncertainty in this case is trivial:

   delta( 3.0 + delr) = delta(3.0) + delta(delr)

3.0 is a constant, so the error bar in the path length is the same as 
the error bar in the variable.


HTH,
B



--
 Bruce Ravel   bra...@bnl.gov

 National Institute of Standards and Technology
 Synchrotron Science Group at NSLS-II
 Building 743, Room 114
 Upton NY, 11973

 Homepage:http://bruceravel.github.io/home/
 Software:https://github.com/bruceravel
 Demeter: http://bruceravel.github.io/demeter/
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