From:   SMTP%"Fraser.Rowan@awe.co.uk"  9-JAN-2001 17:30:13.43
To:     cockcroft@gordon.cryst.bbk.ac.uk
CC:     
Subj:   PD00 Assignment


Jeremy,
                Sorry to be bothering you again, but I have a query about an
example which is set in the course notes. Release 5, Symmetry I, Rotation
Symmetry sub-sect.II Symmetry operators, third last paragraph ending "Thus
the symmetry operator for a twofold rotation axis at, for example, (0,1/4,z)
is -x,1/2-y,z." 

                When proving a symmetry operator I would plug in values of a
hypothetical position (e.g. 1,1,1). If, however, you perform a two fold
rotation about point (0,1/4,z) originating from (1,1,1) the final point will
be (-1,-3/4,1), however, the symmetry operator dictates that the final point
should be (-1,-1/2,1). Is this is typo in the course notes or have I
completely got the wrong end of the stick? (As you may have gathered I am
having big troubles with question 5 - I put it down to not being able to
think in 3-dimensions.)

Best regards,
                        Fraser
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