[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
>>>
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>>
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> --
>
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