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*To*: ccp4 bulletin board <ccp4bb@dl.ac.uk>*Subject*: Re: NCS worries*From*: "Hazes B." <bart@mrc-lmb.cam.ac.uk>*Date*: Tue, 29 Jun 1999 16:40:52 +0100 (BST)*Reply-To*: "Hazes B." <bart@mrc-lmb.cam.ac.uk>*Sender*: owner-ccp4bb@dl.ac.uk

*** For details on how to be removed from this list visit the *** *** CCP4 home page http://www.dl.ac.uk/CCP/CCP4/main.html *** Two people have pointed out to me that calculating a "self-Patterson" using your observed intensities and all phases set to zero" is strange since intensities don't have phases. I agree. However, to calculate a Patterson you have to generate map coefficients by multiplying the structure factor with its complex conjugate which gives coefficients that are the square of the original structure factor amplitude and a phase of zero. Since the square of the structure factor amplitude is proportional in magnitude to the measured intensity this means that you can use the intensity for this calculation, but of course you can use F-squared if you prefer (perhaps your preference depends on the FFT program you are using to calculate the map?). It may be useful to calculate your "self-Patterson" at relatively low resolution (e.g. 6 to 999 Angstrom) because you will then be able to spot pseudo translational symmetry even if it is very pseudo. Bart

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