Re: Masking

[Edward Berry <eaberry@lbl.gov>]

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Fred. Vellieux wrote:
> In fact, you will be using the mask in the INITIAL cycle.
> 
And using the mask, or an improved mask, in all subsequent
cycles, I presume? Then I think you agree with Dave Schuller,
> > there is no such thing as maskless averaging.


And I agree with everything else you said, including that this
single cycle of maskless averaging, without calculating phases,
would provide improved density for auto-generation of a mask.
And I realize now this is what Jim Naismith must have been
suggesting:
> Is there a way to harness the averaging to generate a better map from 
> which to derive the solvent mask?
> 
> Effectively a single run of maskless averaging.

	(this would be trivial to implement, using 
	RAVE with a huge spherical mask or a rectangle 
	the size of the cell)

But I think most of us, when we think of density averaging, think
of an iterative procedure including phase calculation, whereby
the averaging step is used to impose the constraints Michael Rossman 
invoked due to redundancy of information resulting from  NCS or 
multiple crystal forms, and thus improve the phases. For that
I agree with Dave Schuller that there has to be a mask, whether 
user-supplied or autogenerated.

Ed