Is there any tensor that gives the radius of a sphere?

[cozycoz]

Can I calculate a tensor of a system( lots of particles) shaped like a sphere, then get exactly the radius of the system?

(I want to get lengths of three axes of ellipsoid, and I'm trying to examine the way with a sphere. )

 

[Orodruin]

I’m sorry, but I think it is not at all clear what you are after. Can you perhaps elaborate?