Phil, It also affects centred monoclinic: to avoid some cases of beta > 120 you have to use the I121 setting instead of C121 (and it is a conventional setting, see IT vol. A pp.126-7). For example the conventional (but non-standard) I121 setting: a=50 b=60 c=51 beta=90.2 would I think be re-indexed by pointless to the unconventional (but standard) C121 setting: a=71.3 b=60 c=50 beta=134.3.
Trigonal, tetragonal & hexagonal settings with a or b unique are definitely not only non-standard but also non-conventional: they violate Table 9.3.4.1 in IT Vol. A and they don't appear in the diagrams, so let's not go there! The point about the IUCr convention is that the cell is determined by the rules in Table 9.3.4.1 so you would never get into that situation. For the oP lattice the cell is determined once and for all by the rules in exactly the same way: the systematic absences are not taken into account because they are not always reliable, e.g. it may be only after you've solved the TF that you can assign the SG correctly, or at least beyond reasonable doubt, and re-indexing at that point makes no sense. To summarise my POV: I don't really care which convention you use, but I think gratuitous re-indexing (i.e. without the user specifically asking for it) is just very confusing, and this is what can happen if you stick to the standard settings. I'm all for educating users, and re-indexing 1 or 2 datasets can be very educational, but if you have lots of datasets to deal with it's no longer amusing! Sometimes re-indexing *is* needed, e.g. because you already have isomorphous protein-ligand structures and you want to be able to compare them easily, but this should *only* be done to conform to a reference dataset. I don't see any point in re-indexing just to conform to the 'standard setting' 'non-convention' which is derived from a mis-reading of the 1952 ed of IT (my guess is they didn't list all the conventional settings because the publisher wanted to save money! - but at least they saw sense for the 1983 ed.). In any case this will only affect users of Arp/Warp, all other CCP4 programs (and most non-CCP4 programs, e.g. Shel-X, CNS etc) can handle non-standard settings, and if you use Mosflm and always specify SG P222 for all oP cases (which I always do anyway), you would have to re-index anyway. -- Ian > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Phil Evans > Sent: 24 September 2007 16:58 > To: CCP4BB@JISCMAIL.AC.UK > Subject: Re: [ccp4bb] arp/warp in p22121: what to do in Pointless > > I think this is only a problem in the primitive orthorhombic system > (at least I assume people don't want hexagonal axes along a, A & B > centred lattices etc, although there is no reason in > principle why not). > > Following some earlier discussions with Ian, Pointless now honours > (and preserves) a reference file (HKLREF) in eg P 2 21 21, and also > explicit reindex operations, but an initial indexing will still > enforce the "standard" setting eg P 21 21 2, because I accept the > "reference" setting from the cctbx library > > ie suppose you have a crystal which when indexed with a <= b > <= c and > Pointless decides unambiguously for the sake of argument) that the > axis along a is a 2-fold and the other two are 2(1) screws, ie space > group P 2 21 21. > > At present this will be reindexed to the "standard" setting P 21 21 > 2, but is that what you want, or should it be left as a<b<c? Which > criterion takes precedence? > > Phil > > > On 19 Sep 2007, at 17:54, Ian Tickle wrote: > > > Hi Sue > > > > It's certainly true that the convention in the 1935 and 1952 > > editions of > > IT Volume 1 *appeared* to be the 'standard setting' > convention that > > you > > describe because only the 'standard' settings were listed, > and this > > was > > the way that many crystallographers interpreted it (actually only > > macromolecular crystallographers, the small molecule people stick > > to the > > IUCr convention), so this is probably where you're coming from. > > However > > the 1983 edition of Volume A clarified the situation and > made it clear > > that this was never the intention, so all the conventional > settings > > are > > now shown on the SG diagram pages. P22121 & P21221 certainly are > > defined in IT Vol. A - look on the diagram page for SG no. > 18 & you'll > > see them. > > > > The 'standard symbol' for a space group is merely the heading on the > > page used only for indexing purposes, so space groups P22121, > > P21221 and > > P21212 all have the same standard symbol P21212; hence the standard > > symbol is not unique and can't be used to unambiguously define the > > space > > group. The 'standard setting' is merely the space group > setting that > > has the same name as the standard symbol. Even if that weren't > > true do > > we really want to be still sticking to a convention that > was abandoned > > 25 years ago and doesn't a later convention override an earlier one > > anyway? > > > > Actually the convention in use is not the issue anyway, I don't care > > which convention is used as long as all programs use the same > > convention! - then I'll never need to permute axes (just as > > fundamentally I don't care which co-ordinate format is used > as long as > > all programs use the same one, then I'll never need to > reformat). So > > Mosflm uses the IUCr convention (i.e. a<=b<=c for primitive > > orthorhombic), and therefore any program which doesn't support that > > convention for any space group forces you to permute the axes > > completely > > unnecessarily. > > > > -- Ian > > > >> -----Original Message----- > >> From: Sue Roberts [mailto:[EMAIL PROTECTED] > >> Sent: 19 September 2007 16:38 > >> To: Ian Tickle > >> Subject: Re: [ccp4bb] arp/warp in p22121 > >> > >> Hi Ian > >> > >> But there's an older convention, which is to use the space groups > >> settings defined in the International Tables - and P22121 is not a > >> standard setting. > >> > >> Sue > >> > >> > >> On Sep 19, 2007, at 8:18 AM, Ian Tickle wrote: > >> > >>> I'm confused now, sticking to the IUCr convention should not > >>> require any > >>> axis permutation. My beef is specifically against > unnecessary axis > >>> permutations! Surely it's when the program doesn't support the > >>> convention that you are forced to permute the axes? > >>> > >>> Besides I did solve a structure in P22121 with Phaser so > >> I'm even more > >>> confused! > >>> > >>> -- Ian > >>> > >>>> -----Original Message----- > >>>> From: [EMAIL PROTECTED] > >>>> [mailto:[EMAIL PROTECTED] On Behalf Of Airlie McCoy > >>>> Sent: 19 September 2007 15:09 > >>>> To: CCP4BB@JISCMAIL.AC.UK > >>>> Subject: Re: [ccp4bb] arp/warp in p22121 > >>>> > >>>>> The problem is specifically that ARP/wARP *doesn't* > >> support the IUCr > >>>>> convention as given in IT (Vol. A, >= 1983 edition, Table > >>>> 9.3.4.1, p.758 > >>>>> in 5th ed.) regarding choice of cell in primitive > >> orthorhombic space > >>>>> groups, and I suspect in centred monoclinic ones also. > >>>> AFAIK ARP/wARP > >>>>> and pointless are the only two CCP4 programs that currently > >>>> don't fully > >>>>> support the IUCr convention > >>>> > >>>> Phaser doesn't "support" the IUCr convention, and if it was > >>>> used for the > >>>> original MR in this case (I don't know whether it was or > >>>> not), then it > >>>> would have caused the "problem". We have had user requests to > >>>> change the > >>>> output to the IUCr convention, but other people get confused > >>>> if the axes > >>>> are permuted. So the choice will be made an output option - > >>>> Frank von Delft > >>>> suggested the keyword "IUCR [ON/OFF]"! Vote for your choice > >>>> of default > >>>> now... > >>>> > >>>> Airlie McCoy > >>>> > >>>> > >>> > >>> > >>> 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 > >>> > >> > >> Sue Roberts > >> Biochemistry & Biophysics > >> University of Arizona > >> > >> [EMAIL PROTECTED] > >> > >> > >> > >> > >> > > > > > > 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 > > 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
