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*To*: Jan Abendroth <Jan.Abendroth@uni-koeln.de>, ccp4bb@dl.ac.uk*Subject*: Re: [ccp4bb]: unmeasured data in map-calculations*From*: "Eleanor J. Dodson" <ccp4@ysbl.york.ac.uk>*Date*: Thu, 21 Dec 2000 09:31:05 +0000*Organization*: Structural Biology Lab. , Dep. Of Chemistry, University of York*References*: <3A40F8C1.D69DA1A8@uni-koeln.de>*Reply-To*: E.Dodson@ysbl.york.ac.uk*Sender*: owner-ccp4bb@dl.ac.uk

*** For details on how to be removed from this list visit the *** *** CCP4 home page http://www.dl.ac.uk/CCP/CCP4/main.html *** Jan Abendroth wrote: > > *** For details on how to be removed from this list visit the *** > *** CCP4 home page http://www.dl.ac.uk/CCP/CCP4/main.html *** > > Dear all, > with many apologizes (because it's mostly a a cns-related question) I > like to submit a question to the ccp4bb. But it's soon x-mass and you > might forgive this. > > My data set is quite incomplete in the highest resolution shell. When I > calculate maps with the cns script model_map the sigmaA-weighted > fofc-map (mFoDFc) has many "unreasonable" peaks at 3sigma-level. When I > make cns to take Fc for the unmeasured Fo's the sigmaA-weighted fofc-map > shows much fewer and much more reasonable peaks, simply this map becomes > significanly better. > > This seems to make sense, but what is the physical/mathematical reason > for this? > How treats cns unmeasured hkl's in the "normal" mode in difference maps? > Is there a related ccp4-option in refmac/fft? > > Thanks for any reply, kind regards and merry christmas > > Jan Obv. if the cns solution is take unmeasured Fobs as = 0.0, then that will mean you are adding in terms -Fc, which would be bad.. But most programs I know leave out any term with Fobs unmeasured, which should be exactly the same as setting Fobs = Fc thus generating a difference of 0.00000 Refmac certainly does set unmeasured Fobs = Fc - the diff maps thus have terms ~ = 0.00 and the 2mFobs-DFc have terms = DFc It gets rid of ripples in the 2mFoDfc at the expense of introducing bias.. No perfect solution except to measure data.. Elranor> -- > ------------------------------ > Jan Abendroth > Institut fuer Biochemie > Universitaet Koeln > Zuelpicher Strasse 47 > D-50674 Koeln > > Tel: +49-(0)221 470 6455 (Labor) > 6445 (Buero) > Fax: +49-(0)221 470 5092 -- ------------------------------------------------------------------ Eleanor J.Dodson, Chemistry Department, University of York, U.K. Tel: Home +44 (1904) 42 44 49, work: +44 (1904) 43 25 65 ------------------------------------------------------------------

**References**:**[ccp4bb]: unmeasured data in map-calculations***From:*Jan Abendroth <Jan.Abendroth@uni-koeln.de>

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