Probably because in the classic implementation it is redundant, D being derived directly from sigmaa.

Some programs refine D and sigmaa (or equivalent terms, such as Lunin's alpha and beta) separately. This is conceptually equivalent to deriving D from sigmaa and refining the scale between Fo and Fc simultaneously with sigmaa.

Kevin


Meyer, Peter wrote:
Slightly off-topic from the original question, but is there a reason that most 
programs don't output D for sigma_a coefficients?

Pete


-----Original Message-----
From: CCP4 bulletin board on behalf of Mayer, Mark (NIH/NICHD) [E]
Sent: Sat 7/5/2008 2:39 PM
To: [email protected]
Subject: [ccp4bb] Definition of Fourier coefficients
Hi,

What do m and D indicate in the Fourier coefficients for a 2mFo-DFc map?

I've dug a bit in web and CCP4 doc  but not found an explanation, though I'm 
sure its there.

Thanks,

Mark



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