Peter, Bart Actually the restraint weight doesn't affect the restraint count one iota and as far as counting is concerned each restraint has exactly one 'vote' in the count. However there is an important proviso: the restraints must be completely independent to contribute fully to the count. Suppose you have a torsion restraint say on an methoxyphenyl group (an example close to my heart since we have endless debates about it!), and suppose the weight on the restraint is absolutely miniscule, but still non-zero (we'd better say it's > than the machine precision to avoid rounding problems). Provided no other restraint or observation (restraints and observations are of course essentially the same thing) affects that torsion angle it will have its full effect, in fact the effect won't depend on the weight. Of course as soon as you have other restraints which affect that same torsion angle they will compete with each other depending on their relative weights, and you can't count them as independent any more.
To answer Peter's original question each *active* restraint is counted. The question of inactive restraints becomes relevant when considering e.g. VDW restraints which normally only become active when the distance becomes less than a threshold. -- Ian > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Bart Hazes > Sent: 14 February 2008 15:53 > To: Meyer, Peter > Cc: CCP4BB@JISCMAIL.AC.UK > Subject: Re: [ccp4bb] counting constraints? > > 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 > > ============================================================== > ================ > > Disclaimer This communication is confidential and may contain privileged information intended solely for the named addressee(s). It may not be used or disclosed except for the purpose for which it has been sent. If you are not the intended recipient you must not review, use, disclose, copy, distribute or take any action in reliance upon it. If you have received this communication in error, please notify Astex Therapeutics Ltd by emailing [EMAIL PROTECTED] and destroy all copies of the message and any attached documents. Astex Therapeutics Ltd monitors, controls and protects all its messaging traffic in compliance with its corporate email policy. The Company accepts no liability or responsibility for any onward transmission or use of emails and attachments having left the Astex Therapeutics domain. Unless expressly stated, opinions in this message are those of the individual sender and not of Astex Therapeutics Ltd. The recipient should check this email and any attachments for the presence of computer viruses. Astex Therapeutics Ltd accepts no liability for damage caused by any virus transmitted by this email. E-mail is susceptible to data corruption, interception, unauthorized amendment, and tampering, Astex Therapeutics Ltd only send and receive e-mails on the basis that the Company is not liable for any such alteration or any consequences thereof. Astex Therapeutics Ltd., Registered in England at 436 Cambridge Science Park, Cambridge CB4 0QA under number 3751674
