Hi Bernhard
Oh dear we're getting into naming issues again!! I'm not clear what's the
distinction you're making between 'A Rice function' and 'THE Rice function'
since my understanding was that there was only one form of Rice distribution,
i.e. the one defined here: http://en.wikipedia.org/wiki/Rice_distribution .
As for the 'Sim function', one problem seems to be that crystallographers
appear to have used this to mean two different things: 1) the PDF of the
*(complex) structure factor*, which is really just a 2-D Gaussian, and 2) the
PDF of the *(real) structure amplitude*, which is the Rice distribution, and
which is the result of integrating out of the phase (which gives the I0
component of the Rice distribution) from the structure factor distribution.
I don't have Sim's original paper to hand so I don't know know how he defined
it, or even whether he ever called his function a 'Rice function'. However it
would seem more logical to call the integrated (Rice) form of Sim's function
'the Sim distribution' and not use this term to mean the 2-D Gaussian.
As for ACNSFD CCNSFD, I'm not clear what you mean, could you be more
specific, in particular do you mean the *structure amplitude* distributions?
Cheers
-- Ian
-Original Message-
From: owner-ccp...@jiscmail.ac.uk [mailto:owner-ccp...@jiscmail.ac.uk] On
Behalf Of Bernhard Rupp
Sent: 09 April 2009 07:06
To: CCP4BB@jiscmail.ac.uk
Subject: Rice vs Sim vs ACNSFD
Dear All,
I am unsure about the likelihood function nomenclature.
I have seen the Sim function called the Rice function, and
aIso have read the acentric conditional normalized structure factor
distribution (ACNSFD)
called the Rice function (the centric conditional normalized structure
factor distribution
consistently seems to be the Woolfson distribution).
Looking at both the Sim and ACNSFD, they look like the
pdf in figure 6 of Rice ( who interestingly, attributes the function
to a Mr Bennett in 'some unpublished work'. So I guess Rice made the
Race).
So believe that
a) both the Sim distribution and the ACNSFD
are A Rice function, not THE Rice function. Agreeable?
b) is there a proper name for the ACNSFD or generally
for the acentric conditional structure factor distribution?
Thx, BR
-
Bernhard Rupp
001 (925) 209-7429
+43 (676) 571-0536
b...@qedlife.com
b...@ruppweb.org
http://www.ruppweb.org/
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