[yt-dev] ramses length units

[Nathan Goldbaum]

This was last touched back in December:

https://bitbucket.org/yt_analysis/yt/pull-request/1335/ramses-unit-conversions/diff
https://bitbucket.org/yt_analysis/yt/issue/939/units-error-in-ramses-frontend

when I updated this, I attempted to set the units in exactly the same way
as pymses. Unfortunately since I'm not a ramses user and don't have access
to a diversity of test datasets, it's hard to get this exactly right in all
cases.

Is your dataset cosmological? I wouldn't be surprised if there are subtle
differences in the way units are set up for comoving and non-comoving
simulations.

On Thu, Jun 4, 2015 at 2:59 PM, Desika Narayanan <dnarayan at haverford.edu>
wrote:

> Hey YT-dev,
>
> I've discovered something that I think could maybe be a bug (though maybe
> not) in the Ramses front end but am unsure about the motivation behind the
> code so thought I'd check in and try to learn a bit.
>
> In frontends/ramses/data_structures.py, I think the length_unit is set to
> be the length_unit that comes from the info_xxx.txt file multiplied by the
> box length.   For the example yt data sets, this doesn't impact anything
> because the box lengths are unity.
>
> In examining some Agora snapshots, however the box lengths are not unity -
> one that I'm looking at for example has a boxlen of 600.  This results in
> length units that aren't similar to what the info_xxx.txt file says, and
> more dramatically, mass units that are very different.  For example, in one
> such snapshot, I read from the info file:
>
> boxlen      =  0.600000000000000E+03
> time        =  0.500035810875167E+00
> aexp        =  0.100000000000000E+01
> H0          =  0.100000000000000E+01
> omega_m     =  0.100000000000000E+01
> omega_l     =  0.000000000000000E+00
> omega_k     =  0.000000000000000E+00
> omega_b     =  0.000000000000000E+00
> unit_l      =  0.308656802500000E+22
> unit_d      =  0.157339152800000E-25
> unit_t      =  0.308687241173998E+17
>
> but if I load this snapshot in yt, I get:
>
> >In [2]: print ds.mass_unit
> 9.9935115109e+46 g
>
> >In [3]: print ds.mass_unit.in_units("Msun")
> 5.02586592269e+13 Msun
>
> >In [4]: print ds.length_unit
> 1.851940815e+24 cm
>
> which consequently results in derived quantities from the simulation (like
> stellar mass) that are totally off (by a factor boxlen**3).
>
> So, I'm writing (as a total Ramses novice) to try to understand the
> motivation behind multiplying the length unit by the boxlen in the
> frontend, and if I should be accounting for this factor of boxlen**3 in my
> analysis, or if this is a bona fide bug.
>
> Thanks,
> -desika
>
> ps I updated this morning:
>
> thundersnow:yt desika$ hg id
> 8d3663ac217d+ (yt) tip
>
> _______________________________________________
> yt-dev mailing list
> yt-dev at lists.spacepope.org
> http://lists.spacepope.org/listinfo.cgi/yt-dev-spacepope.org
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.spacepope.org/pipermail/yt-dev-spacepope.org/attachments/20150604/e35fe81c/attachment.html>