[IUCr Home Page] [CIF Home Page]

Index

Macromolecular dictionary (mmCIF) version 2.0.09

_refine_analyze.RG_free_work_ratio

Name:
'_refine_analyze.RG_free_work_ratio'

Definition:

   The observed ratio of RGfree to RGwork. The expected RG ratio
   is the value that should be achievable at the end of a structure
   refinement when only random uncorrelated errors exist in the data
   and the model provided that the observations are properly
   weighted. When compared with the observed RG ratio it may
   indicate that a structure has not reached convergence or a
   model has been over-refined with no corresponding improvement
   in the model.

   In an unrestrained refinement, the ratio of RGfree to RGwork with
   only random uncorrelated errors at convergence depends only
   on the number of reflections and the number of parameters
   according to

                     sqrt[(f + m) / (f - m) ]

   where f = the number of included structure amplitudes and
             target distances, and
         m = the number of parameters being refined.

   In the restrained case, RGfree is calculated from a random
   selection of residuals including both structure amplitudes
   and restraints.  When restraints are included in the refinement,
   the RG ratio requires a term for the contribution to the
   minimized residual at convergence, D~restr~, due to those
   restraints:

            D~restr~ = r - sum [w_i . (a_i)^t . (H)^-1 a_i]

   where

   r is the number of geometrical, displacement-parameter and
     other restraints
   H is the (m,m) normal matrix given by A^t.W.A
   W is the (n,n) symmetric weight matrix of the included
     observations
   A is the least-squares design matrix of derivatives of
     order (n,m)
   a_i is the ith row of A

              Then the expected RGratio becomes

      sqrt [ (f + (m - r + D~restr~))/ (f - (m - r + D~restr~)) ]

              There is no data name for the expected value of RGfree/RGwork yet.

   Ref: Tickle, I. J., Laskowski, R. A. & Moss, D. S. (1998).
        Acta Cryst. D54, 547-557.


Type: float

Mandatory item: no

Alias:
_refine_analyze.ebi_RG_work_free_ratio (ebi_extensions version 1.0)
The permitted range is [0.0, infinity)

Category: refine_analyze