[Chimera-users] Principal axis of inertia

Tom Goddard goddard at cgl.ucsf.edu
Fri Mar 21 23:55:22 PDT 2008

Oops.  That script I posted for calculating the inertia of a molecule 
had some problems.  The printed matrix of axes was transposed though the 
correct axes were used for the displayed ellipsoid.  Also I was using 
inertia matrix I_ij = sum_over_k(m_k*r_ki*r_kj) omitting the diagonal 
term.  Should have been I_ij = sum_over_k(m_k*(|r_k| - r_ki*r_kj)).  And 
finally I incorrectly computed the ellipsoid size along each axis.  
Everything was a little bit wrong.  Here's the fixed version.  Tested in 
Chimera version 1.2500 but should work with earlier versions.


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