Rg of clusters

[jude vishnu]

Hi everyone,

I just have a small confusion regarding what the gyration tensor and Radii_of_gyration returns in the cluster module. 

Is it returning $ Rg^2$ or  $ \sqrt(Rg^2 )$?

And correspondingly is the gyration tensor returning each component of  $ Rg^2$ or $ \sqrt(Rg^2 )$ ?

Right now I am assuming it returns $ Rg^2 $.

Please let me know if this is correct?

Regards,

Jude

[Bradley Dice]

Jude,

The gyration tensor is computed as described on Wikipedia: https://en.wikipedia.org/wiki/Gyration_tensor

The radii of gyration are computed here as the square root of the trace of the gyration tensor: https://github.com/glotzerlab/freud/blob/048caae9c842cb08b1eeeb45b9dcbd6c49febca0/freud/cluster.pyx#L240

In other words, the radius of gyration has units "length," rather than "length^2".

Particles are assumed to have the same mass. There is an open issue for allowing users to specify per-particle masses. https://github.com/glotzerlab/freud/issues/778

Best,

Bradley