On Apr 16, 2009, at 2:29 AM, James Stroud wrote:
On Apr 16, 2009, at 1:18 AM, Leiman Petr wrote:
I am not sure if it possible to understand _anything_ in
crystallography if it is not clear how to calculate an angle
between two vectors!
More difficult is deciding exactly how to define said vectors in the
first place, especially when one is attempting to define said
vectors for helices "of different subunit[s] in different
orientation[s]".
On second thought it's only slightly less trivial than the angle
calculation: (1) decide the C-alphas of the helix (e.g. DSSP) (2) do
PCA on their coordinates (3) the first principle component defines the
direction of the helix.
