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On 10/11/2011 09:58 PM, Ethan Merritt wrote: > On Tuesday, October 11, 2011 12:33:09 pm Garib N Murshudov wrote: >> In the limit yes. however limit is when we do not have solution, i.e. when >> model errors are very large. In the limit map coefficients will be 0 even >> for 2mFo-DFc maps. In refinement we have some model. At the moment we have >> choice between 0 and DFc. 0 is not the best estimate as Ed rightly points >> out. We replace (I am sorry for self promotion, nevertheless: Murshudov et >> al, 1997) "absent" reflection with DFc, but it introduces bias. Bias becomes >> stronger as the number of "absent" reflections become larger. We need better >> way of estimating "unobserved" reflections. In statistics there are few >> appraoches. None of them is full proof, all of them are computationally >> expensive. One of the techniques is called multiple imputation. > > I don't quite follow how one would generate multiple imputations in this case. > > Would this be equivalent to generating a map from (Nobs - N) refls, then > filling in F_estimate for those N refls by back-transforming the map? > Sort of like phase extension, except generating new Fs rather than new phases? Some people call this the "free-lunch-algorithm" ;-) Tim > Ethan > [...] - -- - -- Dr Tim Gruene Institut fuer anorganische Chemie Tammannstr. 4 D-37077 Goettingen GPG Key ID = A46BEE1A -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.10 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iD8DBQFOlVi4UxlJ7aRr7hoRAlU+AKDo+c449pUQ/1cnQAl6SMRqzVkp6wCcDETj GHB8hFXt1McbxWHfpUAsHtE= =FOWk -----END PGP SIGNATURE-----
