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Re: Neutron diffraction experiments

  • To: Multiple recipients of list <coredmg@iucr.org>
  • Subject: Re: Neutron diffraction experiments
  • From: Howard Flack <Howard.Flack@cryst.unige.ch>
  • Date: Wed, 25 Feb 1998 18:14:34 GMT
Since everyone is allowed at least two tries:

>         The _refine_diff_density_ fields are used for diagnostic purposes
> to ensure that the refined model gives an adequate fit to the
> measurements. 

For this type of diagnostic field why not make the values dimensionless.
Divide the experimental value by a "standard" value in the same units. I
would not recommend such a technique for values that have real
quantitative significance.

> In CIF one would need some other syntactic device, e.g.
>    _refine_diff_density(units=fm/A^3^)   0.903

     _refine_diff_density  0.903 [fm A^-3^]
  is the most natural and corresponds to the way the children are taught
to do things in school around here. It is in a style identical to that
used for the standard uncertainties, in fact one can have both. The data
item might be defined as having a default unit or no default.

Howard Flack        http://www.unige.ch/crystal/ahdf/Howard.Flack.html
Laboratoire de Cristallographie               Phone:(+41 22) 702 62 49
24 quai Ernest-Ansermet             mailto:Howard.Flack@cryst.unige.ch
CH-1211 Geneva 4, Switzerland                   Fax:(+41 22) 781 21 92

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