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Hi Pete, In your example it would count as 4 restraints, not constraints, and certainly not 4 observations or 4 parameters. It is not clear to me how to quantify the information content in restraints, it probably depends on the type of restraint and surely on the weight. Maybe information theory has some ideas if you are really interested. For real constraints, which fix parameters of the model one way or another, it may be easier. For instance imposing exact NCS 2-fold symmetry reduces the parameters by a factor of 2. Bart Meyer, Peter wrote: > Hi, > > The recent discussion on Rwork/Rfree ratio reminded me of something I was wondering about (*). When counting constraints as observations for determining the observation to parameter ratio, is each unique constraint counted, or each time a given constraint is used. For example, if there are 4 carbon oxygen bonds (assuming the same parameters, let's say serine beta-carbon to serine gamma-oxygen), would this count as 4 constraints as observations, or 1? > > Intuitively, it seems to me like it should be counting unique constraints (although as near as I can tell these aren't listed in refmac5 logfiles). But I don't have a clear explanation for why, and of course I could be wrong on this. > > > Thanks, > > > Pete > > * Rough translation - I'm about to ask another stupid question. Not like it's the first time. > > -- ============================================================================= Bart Hazes (Assistant Professor) Dept. of Medical Microbiology & Immunology University of Alberta 1-15 Medical Sciences Building Edmonton, Alberta Canada, T6G 2H7 phone: 1-780-492-0042 fax: 1-780-492-7521 =============================================================================