Re: [cctbxbb] using scatterer flags?

16 Apr 2013


      I added "use" flag (at the time when I was adding all other scatterer 
flags) rather as a placeholder for a future use, so yes, indeed, 
currently it is not respected in fcalc and gradients calculation (though 
it should be respected!). Perhaps it's time to start using it...

Pavel

On 4/15/13 11:58 AM, Richard Gildea wrote:
...
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 mailto:[email protected]> 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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Re: [cctbxbb] using scatterer flags?

Pavel Afonine