[cctbxbb] Best way to compare incomplete f_hkl to calculated f_hkl

[Ralf W. Grosse-Kunstleve]

Hi Jan,

There are two steps to think about: .map_to_asu() and .common_set()
or .common_sets(). Look for these methods in
cctbx/regression/tst_miller.py, then add print statements to see
how they work (run the command with e.g. "P31" so that it only
exercisesone space group).

However, the best way to compute f_calc given an array of f_obs
is via

  f_calc = f_obs.structure_factors_from_scatterers(
    xray_structure).f_calc()

This way the f_calc are directly compatible with the f_obs array.


Ralf



>________________________________
>From: Jan Marten Simons <marten at xtal.rwth-aachen.de>
>To: cctbxbb at phenix-online.org
>Sent: Monday, April 11, 2011 3:00 AM
>Subject: Re: [cctbxbb] Best way to compare incomplete f_hkl to calculated f_hkl
>
>Hi,
>
>I'm looking at the best (=fastest) way to compare a (possibly incomplete) list 
>of observed reflections f_hkl_obs (or fo2_hkl_obs) to the f_hkl_calc of  
>calculated structure factors or intensities from a model structure.
>
>in miller.py there is a function to calculate a difference between f_obs and 
>f_calc, but it asserts that all reflections are present in f_obs:
>
>def f_obs_minus_f_calc(self, f_obs_factor, f_calc):
>assert f_calc.is_complex_array()
>assert self.indices().all_eq(f_calc.indices())
>assert self.anomalous_flag() is f_calc.anomalous_flag()
>...
>
>In my case it's possible that some reflections could not be observed so they 
>should either be skipped or be assumed to be of zero intensity. As I could not 
>locate the definition for .all_eq(...), yet I'm not sure if this is already 
>handled and if it is how it is done.
>
>Then there is f_obs_minus_xray_structure_f_calc in miller.py as well. Would 
>this be a better approach if the model structure changes quite often? What if 
>I just got f_calc from another source (like doing some custom sped-up partial 
>structure factor calculation)?
>
>In general: What would be your advice on this with cctbx?
>
>
>With regards,
>
>Dipl. Phys.
>  Jan M. Simons
>
>Institute of Crystallography
>RWTH Aachen University
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>
>
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