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> -----Original Message----- > From: Kevin Cowtan [mailto:[EMAIL PROTECTED] > Sent: 21 October 2005 14:16 > To: Ian Tickle; [email protected] > Subject: Re: [ccp4bb]: Phase columns in SigmaA & Refmac. > > csigmaa (the clipper util) does it too. > > The reason is that when you are outputting map coefficients, the > convention is that when a coefficient calculated with > difference terms > (2mFo-DFc), (mFo-DFc) goes negative, you invert the phase instead of > giving a negative coefficient. So the phases, while usually the same, > are occasionally different. (You could argue that this is a dumb > convention). Yes, there's usually some rationale behind conventions, but in this case I can't see what it could be: it has no upside and it has a big downside of allowing the possibility of disastrous mistakes. Negative numbers work just as well as positive ones in polar co-ords! > > In the csigmaa case, there is an additional reason: it outputs column > groups instead of columns. You can't output a map coefficient > without a > phase, or share a phase between several groups. That objection would be answered by my suggestion of outputting 3 phase columns with different labels but identical phase values, since there are several reasons why we can't simply delete 2 of the phase columns. -- Ian ********************************************************************** CONFIDENTIALITY NOTICE This email contains confidential information and may be otherwise protected by law. Its content should not be disclosed and it should not be given or copied to anyone other than the person(s) named or referenced above. If you have received this email in error, please contact [EMAIL PROTECTED] **********************************************************************
