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Hi Pietro,

I would use pointless for this - it will correctly reindex the
reflections and sort them to boot. You can specify the correct
pointgroup and reindex operator to reindex the reflections, and (I am
99% sure) pointless will compute the correct unit cell...

You can find recent versions of pointless which do this, and
documentation on how to do this, on the ccp4 prerelease pages.

Cheers,

Graeme 

-----Original Message-----
From: CCP4 bulletin board [mailto:[log in to unmask]] On Behalf Of
Pietro Roversi
Sent: 07 March 2008 18:18
To: [log in to unmask]
Subject: [ccp4bb] MTZ cell troubles after sortmtz reindexing from P321
to C2

Dear all,
               after much sweat and grief I managed to index my data in
P321 but looking at the symmetry I think they might be C2: reindexing
from P321 to C2 with the 2h+k, k, l operator in sortmtz produces the
right cell (and yes I did tick the "Reduce reflexions to the asymmetric
unit" button so that noreduce is not among the sortmtz keywords): 

P321 209.3168  209.3168   40.6822   90.0000   90.0000  120.0000
C2 362.5473  209.3168   40.6822   90.0000   90.0000   90.0000

But: scala then decides that the asymmetric unit is not the right one
and it mysteriously changes cell parameters (which I think points to a
bug in the sortmtz process of reindexing):

Reciprocal space symmetry: 
Space group: "C 1 2 1" Point group: "PG2" Laue group: "2/m" 
Reference asymmetric unit: "k>=0 and (l>0 or (l=0 and h>=0))" 
  (change of basis may be applied) 

and I end up with this C2 cell in the mtz output from scala:

285.9320  285.9320   40.6824   90.0000   90.0000   90.0000

I have tried OUTPUT ORIGINAL ans some such in scala but to no avail.

Now please don't all tell me to go back and reindex-reintegrate these
images - although I might have to do it to get the best out of these
data once I am convinced they are monoclinic. 

Rather, I would appreciate suggestions on what program to feed the
multirecord mtz to sort its asymmetric unit in C2 so that scala does not
play tricks on me; or what keyword to feed scala to keep reflexions in
the current asymmetric unit (and use cad or sftools afterwards on the
scaled/merged file)

Thanks

Pietro  



--
Pietro Roversi
Sir William Dunn School of Pathology, Oxford University South Parks
Road, Oxford OX1 3ER, England UK Tel. 0044-1865-275385