[cctbxbb] reflection conditions for non-standard settings

[Ralf W. Grosse-Kunstleve]

Hi David,

cctbx does not include lists of reflection conditions as you find them in the International Tables.


It is very easy and fast to derive the reflection condition for a given hkl directly from the symmetry operations. See the code near the top of cctbx/sgtbx/miller.cpp. This is what we use for all practical applications. For example:

  from cctbx import sgtbx
  sg = sgtbx.space_group_info("19").group()
  print sg.is_sys_absent((1,2,3))

  print sg.is_sys_absent((0,0,3))


I have C code given to me by Maxim Larine and Slava Klimkovich in 1997 which computes the conditions, but it involves inefficient grid searches.

I think a good solution would be to tabulate the conditions for the 230 reference settings and figure out the transformation law to obtain the conditions for arbitrary settings via a change of basis. But I yet have
to find a practical motivation for spending the effort implementing this.


If you find that Phil has a solution, it would be nice to move it into
cctbx.

Ralf



>________________________________
>From: David Waterman <dgwaterman at gmail.com>
>To: cctbxbb at phenix-online.org
>Sent: Saturday, June 4, 2011 3:28 AM
>Subject: [cctbxbb] reflection conditions for non-standard settings
>
>
>Hi,
>
>
>I'm new to cctbx and to this mailing list, so please let me first apologise if the answer to this question should be obvious, or lies in the archive.
>
>
>I want a list of general reflection conditions for all space groups and settings listed in the CCP4 file syminfo.lib. At first I thought I could get this information from the online version of ITC vol A, but I soon realised that only certain standard settings are included. To avoid deriving them all by hand from the symop and cenop lines, I wonder if there is a foolproof way I can get this information from cctbx, but I don't know where to begin. Perhaps something in sgtbx?
>
>
>Many thanks
>
>-- David
>
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