[Yt-dev] minimum halo mass

[Matthew Turk]

> 1.  Given the cosmological parameters from the Enzo parameter file,
> calculate the theoretical halo mass function using Press-Schechter or
> the equivalent (the Warren et al. mass function is actually the best
> one to use).
> 2.  Figure out what the largest halo is that has at least a 50%
> probability of being inside the halo volume (in other words, what is
> the largest halo mass where you get 0.5 halos/box?)
> 3.  Use the relationship between virial mass and virial radius to
> calculate a radius, and then scale it into box units.
> 4.  Double that number and call that the padding.

This is a good idea.  I like this idea.  It's straightforward and
*easy to justify*.

> 1.  One needs to assume a value of \sigma_8, since it's not actually
> in the Enzo parameter file.  This isn't a big deal - it's somewhere
> between 0.8 and 0.9 for pretty much any simulation.  For safety, I'd
> suggest we just pick 0.9, since that gives an overall higher mass
> function (and is thus the more conservative choice).

I agree.

> 2.  This method of estimating padding only works for cosmology
> simulations.  If one does non-cosmology particle simulations (which I
> could see happening in the future, if Enzo is adopted more widely)
> then people will have to specify their own padding.  We can always
> cross that bridge when we get to it.

I do agree, and I think that specifying one's own padding is
acceptable, it just should be a reasonable guess for cosmo runs, I
felt.

> I have a press-schechter code that I am happy to donate to the cause.
> It's written in C, though, so somebody's going to have to mess around
> with it a bit.  I don't have time, sadly, so I'd have to ask for
> somebody else to volunteer...

I'll take care of it; if you can send it my way, I'll take a look at
it, and it can ferment my mind grapes for a little while and I'll hit
it hard mid-April.  Until then, I think everyone who needs parallel
hop has already figured out the padding issue, so we should be set.  I
think this could be a useful set of code to include in any event!

Thanks, Brian!

-Matt