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[ccp4bb]: I to F

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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


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.
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 > 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