[phenixbb] Why the correlation coefficient of the electron density with the model is never 1?

[Pavel Afonine]

Hi Murpholino,

reasons are similar to why crystallographic R factor never goes to zero.

Model-map CC is calculated between the map (the data, in case of cryo 
EM, or sort of data in case of Crystallography) and a model. As you know 
data always has errors and model is just an approximation to reality. So 
you have no chance to match them perfectly, unless overfit. Something 
along these lines..

Pavel

On 6/14/19 12:42, Murpholino Peligro wrote:
> The links below show a plot of the results of 
> phenix.real_space_correlation* for a nice lisozyme crystal and also 
> the coot view.
> https://drive.google.com/open?id=0B9tqXyDsq9YIdkRhcVFXU2dEdnhINXR6Y3hza2Y5NGpNM1hV
> https://drive.google.com/open?id=0B9tqXyDsq9YIREd1OFZhNGZtRnN4aldtVU1mdk84NExVX2Vn
>
> As you can see the electron density fits very well the model.
> Why not a single residue gets a perfect correlation coefficient? (i.e. 1)
>
>
> Just curious.
>
> Thanks
>
>
> * phenix.real_space_correlation pdbfile mtzfile --detail="residue" > outpu
>
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