Hello Stephen, This is part 2 of the ellipsoid parameter finding. The method is outlined mainly in the Dubinski and Carlberg 1991 paper. But since we are doing this in YT and we already know the particle list to begin with, I put in the option that the user can specify if they want all the particles in the region to be taken into account or only the particles found by the halo finder algorithm. This is an option that I think should be amended to the first ellipsoid parameter finder. The script form is linked here: http://paste.enzotools.org/show/1782/ Once I have written out the methodology for myself, I'll work on the YT documentation, will probably need some help in this area when it comes to it. Doron Lemez has used this method in his paper and helped me tested the accuracy of this script. I was wondering do I need to ask him if he wants his name in the credits, or just mention his name as a special thanks? One thing he did in the paper that was especially useful is defined the starting sphere to have 2x the virial radius. Without that specification, I run into non-convergence sometimes, where after many iterations I end up with no particles. And I want to mention again that there's no guarantee that any or all the haloes will converge with this method. I tried to adhere to the PEP8 formatting, but old habits die hard so I'm sure I made mistakes in the formatting, let me know if you see them. From G.S.