[cctbxbb] reflection conditions for non-standard settings

Ralf W. Grosse-Kunstleve rwgk at yahoo.com
Sat Jun 4 13:03:44 PDT 2011

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


>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
>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
>cctbxbb mailing list
>cctbxbb at phenix-online.org
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