Hi The relations are in International Tables Vol A; in the 2006 edition you find them in section 9.2 by P.M. de Wolff, pp 750 - 755; the transformations for the 44 characteristic lattices (or lattice characters...) are in Table 9.2.5.1.
In Mosflm, the autoindexing penalties are based on the differences between the result of the transformations applied to the real triclinic basis and what you would get if the result was perfect. On 13 Nov 2012, at 09:55, vincent Chaptal wrote: > Dear all, > > I am not sure I understand point groups and relations between groups and > subgroups anymore, and would appreciate some guidance. > > I was under the impression that all point groups were related to an original > P1 cell, and that by applying specific lattice symmetries, one could "get" > higher point groups. Thus, if one knows the symmetry operators, one could > jump from one point group to another. Inspection of the reflections can then > determine the "real" point group and space group. > At least that's what I thought Mosflm was doing? Am I correct? > P1 +(symm-opp)>C2 + (symm-opp2)>P3 > same P1 +(symm-opp3)> P2 + (symm-opp4)>P222 .... > If that's the case, could someone point to me where to find these symmetry > opperators (International tables?), because it's not obvious to me. > > Or are these relations between groups and subgroups only true for certain > crystals where the cell parameters are specific, and allows a symmetry > operator to generate a higher symmetry point group? > > Thank you for your help. > vincent Harry -- Dr Harry Powell, MRC Laboratory of Molecular Biology, MRC Centre, Hills Road, Cambridge, CB2 0QH Chairman of European Crystallographic Association SIG9 (Crystallographic Computing)
