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*To*: ccp4bb@dl.ac.uk*Subject*: [ccp4bb]: I to F*From*: Phil Evans <pre@mrc-lmb.cam.ac.uk>*Date*: Thu, 16 Nov 2000 10:18:46 +0000 (GMT)*In-Reply-To*: <3A13AD57.7831F894@holyrood.ed.ac.uk>*References*: <3A13AD57.7831F894@holyrood.ed.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 *** But truncate does all this stuff properly A comment on your mail, why did you send this plaintext message as an attachment? It just makes it harder to read, & is unnecessary & irritating Phil Dmitriy Alexeev writes: > What the weak F's are for? For better refinement, OK! What is the major > danger of including them? Artificially low sigF's - not to overweight > the arbitrary assigned poorly measured F's. The estimate sigF=sqrt(sigI) > is as fine as any other, except for few (but very important for ML > refinement) cases when sigI is accidently too small - it happens if the > data redundancy is low. I suggest to introduce a lower limit for sigF > and derive it from the well measured reflections. > Indeed, in absence of systematic errors and for well measured > reflections > > sigI->const*sqrt(I) and sigF=0.5*sigI/F. Then: > sigF->const*sqrt(I)/F=const, which is the estimate for min(sigF) > > I compute this constant and top sigF's up to this level. For good data > (statistical noise only) this const is really constant throughout all > the intensisty range (I tested it). Actually, the variability of > min(sigF) might be used as an indicator of systematic errors. > Dmitriy Alexeev, Edinburgh. > begin:vcard > n:Alexeev;Dmitriy > tel;fax:(44)01316507055 > tel;work:(44)01316507047 > x-mozilla-html:TRUE > adr:;;;;;; > version:2.1 > email;internet:dima@holyrood.ed.ac.uk > fn:Dmitriy Alexeev > end:vcard

**References**:**[ccp4bb]: I to F***From:*Dmitriy Alexeev <dima@holyrood.ed.ac.uk>

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