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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
> 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.
> fn:Dmitriy Alexeev