[sharp-discuss] missing ISYM

Phil Evans pre at mrc-lmb.cam.ac.uk
Tue May 18 18:45:58 CEST 2010


I agree it should be fixed (one way would be to use F+ & F- instead of <F> and DANO). The reason it is a bit marginal is that in most datasets the number of reflections without both F+ and F- measurements is small

Phil

On 18 May 2010, at 17:38, Gerard Bricogne wrote:

> 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
>>> 
>>> _______________________________________________
>>> sharp-discuss mailing list
>>> sharp-discuss at globalphasing.com
>>> https://www.globalphasing.com/mailman/listinfo/sharp-discuss
>> 
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> 
> -- 
> 
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>     *                                                             *
>     * Gerard Bricogne                     gb10 at GlobalPhasing.com  *
>     *                                                             *
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