Hi Francisco,
I'll play devil's advocate, but a measurement without an estimate of its
error is closer to theology than to science. The fact that the standard
deviations are not used for calculating an electron density map via FFT is
only due to the hidden assumption that you have 100% complete, error-free
data set, extending to sufficient high (infinite) resolution. When these
assumptions do not apply (as is usually the case with physical reality),
then the simple-minded FFT is not the correct inversion procedure (and the
data do not univocally define a single map). Under these conditions other
inversion mathods are needed (such as maximum entropy) for which the
standard deviations are actively being used for calculating the map.
My twocents,
Nicholas
On Tue, 22 May 2012, Francisco Hernandez-Guzman wrote:
> Hello everyone,
>
> My apologies if this comes as basic, but I wanted to get the expert's
> take on whether or not the sigmaF values are required in the calculation
> of an electron density map. If I look at the standard ED equation,
> sigma's don't appear to be a requirement but all the scripts that I've
> looked at do require sigma values.
>
> I wanted to calculate the electron density for PDB id: 1HFS but the
> structure file only lists the Fo's, Fc's and Phases, but no sigmas.
> Would such structure factor file be considered incomplete?
>
> Thank you for your kind explanation.
>
> Francisco
>
--
Nicholas M. Glykos, Department of Molecular Biology
and Genetics, Democritus University of Thrace, University Campus,
Dragana, 68100 Alexandroupolis, Greece, Tel/Fax (office) +302551030620,
Ext.77620, Tel (lab) +302551030615, http://utopia.duth.gr/~glykos/
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