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Well an R factor is generally defined as Sum |Xobs - Xcalc| / Sum |Xobs| where X can be replaced throughout by almost anything you like (within reason), so if you wanted to you could replace X by the dispersive difference and quite possibly get a meaningful quantity: but please don't call it 'anomalous R_Cullis' or you will confuse the hell out of everybody! But clearly replacing X by a quantity which is always zero is completely pointless. -- Ian > -----Original Message----- > From: William Scott [mailto:[EMAIL PROTECTED] > Sent: Thursday, May 18, 2006 3:11 PM > To: Philippe DUMAS > Cc: Ian Tickle; [email protected] > Subject: RE: [ccp4bb]: Anomalous Cullis Rfactor > > > I thought the only difference between the magnitude > of F+ and the magnitude of F- would come from the > imaginary component to F, which centrics won't have. > If dispersion contributes, the contribution is the real component > to the vector, and hence the same magnitude resultant > for both F+ and F-. > > > > > On Thu, 18 May 2006, Philippe DUMAS wrote: > > > Hi everybody > > > > Centric reflections have no anomalous signal at a single > wavelength; that's > > true ! > > But they are sensitive to dispersive effects. So a > "dispersive R_Cullis" > > should be meaningful. > > Am I wrong ? > > > > Philippe Dumas > > IBMC-CNRS, UPR9002 > > 15, rue René Descartes 67084 Strasbourg cedex > > tel: +33 (0)3 88 41 70 02 > > [EMAIL PROTECTED] > > > > > > > > > > -----Message d'origine----- > > De : [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] > la part de > > Ian Tickle > > Envoyé : jeudi 18 mai 2006 15:41 > > À : [EMAIL PROTECTED] > > Cc : [email protected] > > Objet : RE: [ccp4bb]: Anomalous Cullis Rfactor > > > > > > *** For details on how to be removed from this list visit the *** > > *** CCP4 home page http://www.ccp4.ac.uk *** > > > > > > > > Hi Bill > > > > Which program is reporting anomalous R_Cullis for centrics? > If that's > > really what it's doing then it's not defining anomalous > R_Cullis in the > > 'conventional' way, i.e.: > > > > Sum |delta_anom_obs - delta_anom_calc| > > -------------------------------------- > > Sum |delta_anom_obs| > > > > For centrics all these terms are, or should be zero, so you > would get > > 0/0 - not a well-defined quantity! > > > > -- Ian > > > >> -----Original Message----- > >> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On > >> Behalf Of William Scott > >> Sent: Wednesday, May 17, 2006 6:41 PM > >> To: [email protected] > >> Subject: [ccp4bb]: Anomalous Cullis Rfactor > >> > >> *** For details on how to be removed from this list visit the *** > >> *** CCP4 home page http://www.ccp4.ac.uk *** > >> > >> > >> Hi everyone: > >> > >> How is an anomalous Cullis R defined for centric reflections? > >> (If it > >> is the F+ - F-, how can that be meaningful?) > >> > >> Thanks. > >> > >> Bill Scott > >> > >> > >> > >> > > > > Disclaimer > > > > This communication is confidential and may contain > privileged information > > intended solely for the named addressee(s). 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