[cctbxbb] using scatterer flags?

[Richard Gildea]

Are the same scatterers contributing to f_calc for every calculation, or
will the scatterers that are contributing vary from calculation to
calculation? In the case of the former it might be simplest to create a new
copy of the xray_structure with only those scatterers.

It looks the "use" flag isn't actually respected in the structure factor or
gradient calculations as far as I can tell. If you feel you need something
like this rather than creating new copies of the xray_structure with only
the scatterers you need or alternatively setting the occupancy to zero,
then this is probably something we can add into the code. There is some
code in cctbx/xray/scatterer_flags.h for flags_set_grad_*() that will set a
selection of gradients all at once in C++, but I don't see an equivalent
for set_use_*(). I suspect that the overhead of looping through the
scatterers to set flags in Python would be small compared to the cost of
calculating the structure factors in the first place.

Cheers,

Richard


On 15 April 2013 10:40, Jan Marten Simons <marten at xtal.rwth-aachen.de>wrote:

> Am Montag 15 April 2013 18:33:00 schrieb Jan Marten Simons:
> > Hi,
> >
> > while working on a really fast way to calculate the structure factors of
> a
> > few millions of different modifications of a structure with only the
> > selected scatterers contributing to f_calc ....
>
> [...]
>
> > (I think building a larger structure and working with
> > selections might be faster than creating lots of different structures
> > containing only the desired scatterers, but I might be wrong on this.)
>
> I've found "flags" might be what I'm looking for. So if I could set the
> "use"
> flag for all scatterers at once and if it was taken into consideration
> during
> structure factor calculation then I think it would most likely be the
> fastest
> way to enable or disable the contribution of individual scatterers to the
> structure factors. Am I right on this and how would I best interface with
> the
> flags mechanism (from python)?
>
> Cheers,
>
> Jan
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