>If we have an atom that is seen by one
>radiation and not by the other there will be a degradation in the quality of
>the parameters by combining the refinement in the current fashion.
Do you mean for example that we might degrade the parameters of a V atom
by introducing neutron data ?
I don
Alan,
I am not suggesting removing reflections. But, I think that we should make
sure that we are combining the data in the best possible way. If we know have
strong information on a vanadium position from X-rays and (extrapolate again)
have only noise from neutrons, then stastically introducing
Oops, forgive the typos! I haven't found a coffee yet :-)
Andrew
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Hi all,
Am I right in thinking there are roughly two camps in this dicussion?
Those who think that adding more data degrades the refinement if that data
is not useful and those who think it makes no difference. (I say 'not
useful' in the context of Vanadium in neutron data or deuterium in x-ray
d
Hi all,
..following a bit the last posting on the topic...
> << I start to be a little bit concerned about all those people claiming and
> pointing out that diffraction don't measure a residual stress but a
> residual strain.
> ..
>
> So, my own idea is that people who don't
Jon Wright wrote:
>I guess the degradation which is found would come from parameters which
>are determined by both datasets and come out with different values in each
>separate refinement.
Not necessarily. In order to get the ESD, the variance-covariance matrix is
multiplied by chi^2, and the
Dear All,
I fully agree with a lot that has been said about at least at increased
ESD's when you combined neutrons with X-ray's. Still there are more than
just a few cases where this is not the case but that is not the point. The
point 'how correct is the ESD?'. I think nobody knows the answer,
As chi^2 is a function of the number of data points included in the
refinement, combined refinements have considerably improved values for a
total chi^2 when compared with refinements carried out against individual
data sets.
Correspondingly the ESDs in the combined refinement output should be
>>I guess the degradation which is found would come from parameters which
>>are determined by both datasets and come out with different values in each
>>separate refinement.
If they come out differently it is because they are differently biased by
different systematic errors in the data not des
On Tue, 25 May 1999 [EMAIL PROTECTED] wrote:
> Not necessarily. In order to get the ESD, the variance-covariance matrix is
> multiplied by chi^2, and the roots of the diagonal elements are taken.
The justification for multiplying by chi^2 is to assume that the
systematic errors are really just
On Tue, 25 May 1999, Alan Hewat, ILL Grenoble wrote:
> >>I guess the degradation which is found would come from parameters which
> >>are determined by both datasets and come out with different values in each
> >>separate refinement.
>
> If they come out differently it is because they are differ
On Tue, 25 May 1999, Alan Hewat, ILL Grenoble wrote:
>
> Mainly because the ESD's are only correctly calculated if the model
> is CAPABLE of fitting the data. This is not usually true when systematic
> errors are important compared to statistical errors, since the model is
> usually not capabl
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