[sharp-discuss] missing ISYM

[Gerard Bricogne]

Dear Phil,

     I don't quite agree that the loss of the ISYM column is "not a huge
loss". It may not make a difference at the moment, but it is actually
critical in exploiting AAS (the anisotropy of anomalous scattering) in the
development version of SHARP, since this phenomenon breaks the equivalence
between symmetry-related reflections, and ISYM is essential in keeping track
of the symmetry relations between the various (then inequivalent) unmerged
measurements. Losing track of ISYM is this context is just as bad as losing
the distinction between I+ and I- in relation to anomalous scattering. 

     See M. Schiltz & G. Bricogne (2008). "Exploiting the anisotropy of
anomalous scattering boosts the phasing power of SAD and MAD experiments", 
Acta Cryst. D64, 711-729.

     Also, in the recent special issue of Acta D containing the Proceedings
of the 2009 CCP4 Study Weekend: M. Schiltz & G. Bricogne (2010). "Broken
symmetries in macromolecular crystallography: phasing from unmerged data", 
Acta Cryst. D66, 325-338.

     I am "surprised and disappointed" that decisions to drop information
can be taken by CCP4 developers without at least some consultation to ensure
that a full and up-to-date scientific picture is taken into account. This
clearly needs to be fixed!


     With best wishes,
     
          Gerard.


--
On Tue, May 18, 2010 at 04:20:55PM +0100, Phil Evans wrote:
> 
> ctruncate does not generate the ISYM column, not a huge loss. In [auto]sharp if you leave the ISYM assignment blank it works for me, I think 

> 
> Phil
> 
> On 18 May 2010, at 15:54, mark.vanraaij at usc.es wrote:
> 
> > Dear all,
> > 
> > As a first-time use, I appear to get stumpe at one of the first  
> > hurdles. My truncate output files do not have the ISYM column, and I  
> > don't see how to "generate" or "keep" the ISYM column in CCP4i.
> > 
> > Mark
> > 
> > _______________________________________________
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> 
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