New issue 1237: HaloMassFcn units (or coments) inconsistent https://bitbucket.org/yt_analysis/yt/issues/1237/halomassfcn-units-or-coment...

spthm:

Disclaimer: I'm not particularly experienced in HMFs. The below may not actually be a bug (just confusing/incorrect comments); if it is, I imagine it relates to issue #1228. It should possibly be a comment on that issue, but I can't confirm the two are related.

For reference, I'm going to link to the current stable yt, 3.2.3.

Based on comments in halo_mass_function.py, I do not believe the stated output units are correct.

halo_mass_function.py:403 multiplies rho_crit_g_cm3_h2 by hubble0**2, resulting in units of Msolar/Mpc^3 for rho0 _if the comment at physical_ratios.py:103 is to be believed_. But line 402 directly above states rho0 in units of h^2 Msolar/Mpc^3.

This error carries through to line halo_mass_function.py:432. It is claimed that dndM_dM_analytic has units of h^3, but it is actually h.

Finally, at halo_mass_function.py:436 we multiply through by h^3, resulting units of h^-2 for dndM_dM_analytic and n_cumulative_analytic (while it is claimed that all h are cancelled out).

Note that halo_mass_function.py:368 has a similar issue, in that h^2 units are claimed, but rho0 has no h dependence. The proceeding usage of rho0 at halo_mass_function.py:390 implies that rho0 indeed should have units h^2 to achieve a h^-1 for thisradius. I think this has a non-trivial impact on the values in sigmaarray, but I gave up trying to track it.

The masses do not appear to be affected, but both analytic output arrays seem to have erroneous factors of h, and I believe the sigma values are also computed with incorrect R values. Since I gave up trying to track how incorrect R impacts sigma, I don't know if this all agrees with the behaviour described by @ioodderskov in #1228.

All that said, if I make the obvious change of not multiplying rho by hubble0**2, the analytic fits do a much worse job of fitting haloes in some of my Gadget-2 snapshots, whereas before agreement with P-S was very good. But I have no idea if this is a fluke, and the simulations are faulty, or whether all of the above is a misunderstanding on my part.

The multiplication by hubble0**2 was introduced in ab0d4e0.