[phenixbb] Twin refinement issues?

[Bryan W. Lepore]

On Fri, 10 Apr 2009, Peter Zwart wrote:
> Twin fractions above 0.5 are physically reasonable! the twin fraction is 
> the size of the twin domain. When you have a twin fraction of alpha, you 
> always have a twin fraction of 1-alpha that goes with it.

this assumes two domains, right?  IIRC, every discussion of twinning i 
have read treats the problem in terms of two domains.  what is the basis 
for only having two domains (besides simplicity)?

someone mentioned a three-domain twinning problem (maybe ccp4 or phenix 
bb, last week or so) - wouldn't that need "1-alpha-(third domain 
fraction)"?

-bryan