30 Jun
2010
30 Jun
'10
4:29 p.m.
Hi Kenneth,
If I set the coordinate_sigma in de .def file to zero will this result in constrained NCS-refinement?
No, sorry, we don't have "strict NCS" in phenix.refine. It is on the list of things to do in the next grant cycle. Some background: phenix.refine uses gradient-driven local minimization, which minimizes a sum of a penalty terms of the form weight * penalty. Examples of "penalty" are (f-obs - f-calc)**2 or (distance_ideal - distance_model)**2, or differences between NCS-related coordinates. weight = 1 / sigma**2, so if sigma is zero you have a divistion by zero. Therefore we use sigma=0 as a flag to turn off the corresponding penalty term. A constraint system is generally much more complicated than a restraint system. Ralf