[Yt-dev] yt-hop configuration improvements?

[Matthew Turk]

Hi Stephen,

I started looking over the code, and the parameters you list below,
and I'm not sure most of them are really terribly relevant to the
depression in the halo count you see.  I'll see if I can change the
code in the next little while, but for my own curiosity, what was the
density threshold you ran with versus the density threshold of the
plot you're trying to reproduce?  And have you run with identical
density thresholds, to see if that alone fixes it?  That parameter is
already tunable.

The other one that I think could be of relevance is the saddle joining
parameter, which is passed as "-dsaddle" to regroup in the standard
Eisenstein distribution.  If you look in hop_regroup.c, though, you
can see that it's been hard-coded by "GLB."  Since I got the code from
the enzo/anyl distribution, not from the Eisenstein distribution, I
think we can safely say that's Greg.  :)

-Matt

On Mon, Mar 23, 2009 at 7:02 AM, Stephen Skory <stephenskory at yahoo.com> wrote:
>
> In hop.c these are the defaults:
>
>    nBucket = 16;
>    nDens = 64;
>    nHop = -1;
>    fDensThresh = -1.0;
>    bSym = 1;
>    bTopHat = 0;
>    nMerge = 4;
>
> bSym and bTopHat are 0/1, nBucket,nSmooth,nDens,nHop, and nMerge are ints, fDensThresh is a float. if fDensThresh is to be >0, it needs to be multipled by the same ratio that the threshold is in SS_HopOutput for it to be correct.
>
> nBucket - Performance tuning in kd-tree search.
> nDens - N_dens -- # of particles to smooth for density, default 64.
> nHop - N_hop -- # of particles over which to look for density max, default 16.
> fDensThresh - Density below which we don't assign to any group, default none.
> bSym - Use gather-only for spline kernal, else gather-scatter.
> bTopHat - Use tophat kernal for density, else cubic spline.
> nMerge - N_merge -- # of particles to catalog group boundaries, default 4.
>
> in regroup.c:
>
>    c->peak_thresh   = 3.0*dens_outer;
>    c->saddle_thresh = 2.5*dens_outer;
>    c->densthresh    = dens_outer;
>    c->mingroupsize = -1;
>
> The defaults are fine here, which puts c->peak_thresh and c->saddle_thresh at a fixed ratio of c->densthresh, but sometimes we want to make them different. Also, the mingroupsize makes a large difference and needs to be adjustible.
>
> c->mingroupsize -- Minimum group size.
> c->peak_thresh - Density required at group center
> c->saddle_thresh - Density required at boundary
> c->densthresh - Density required for a particle to be in a group
>
>
> Let me know if you want help, Matt!
>
>  _______________________________________________________
> sskory at physics.ucsd.edu           o__  Stephen Skory
> http://physics.ucsd.edu/~sskory/ _.>/ _Graduate Student
> ________________________________(_)_\(_)_______________
>
>
>
> ----- Original Message ----
>> From: Matthew Turk <matthewturk at gmail.com>
>> To: yt-dev at lists.spacepope.org
>> Sent: Sunday, March 22, 2009 10:30:24 PM
>> Subject: Re: [Yt-dev] yt-hop configuration improvements?
>>
>> Stephen, why don't you post the list of parameters here, and I'll add
>> them all as keywords inside the C function?  I don't mind doing it.
>> :)
>>
>> -Matt
>>
>> On Sun, Mar 22, 2009 at 10:04 PM, Stephen Skory wrote:
>> >
>> >> I'll try to add these options tomorrow.
>> >
>> >
>> > I'll post the changes to codereview before committing...
>> >
>> >  _______________________________________________________
>> > sskory at physics.ucsd.edu           o__  Stephen Skory
>> > http://physics.ucsd.edu/~sskory/ _.>/ _Graduate Student
>> > ________________________________(_)_\(_)_______________
>> >
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