[Chimera-users] Principal axis of inertia

A. Di Fenza armida.difenza at sns.it
Thu May 14 06:42:55 PDT 2009

Hi Tom,
I saw your message on the web and I tried to use your script on Chimera 1.3. 
Unfortunately it does not work, it give me the following message:

0 models opened

Do you think it is because of the Chimera version? Do you have suggestion?

Thank you very much,

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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