[yt-users] RFC: RAMSES field aliases in yt-3.0

[Sam Geen]

For MHD, the variables stored are the B-field strengths on the faces of 
each cell - the fields in order are: (1) density, (2-4) [x,y,z] 
velocity, (5-7) [x,y,z] B-field left, (8-10) [x,y,z] B-field right, (11) 
pressure (thermal + MHD), then (12+) any passive scalars (metals, etc) - 
see mhd/output_hydro.f90. Note that the MHD module adds 3 variables, so 
the number of variables will be nvar+3.

For RHD (Joki Rosdahl's M1 method implementation, at least - someone 
else will have to help with the ATON version), there is a separate "rt_" 
output file for each CPU (like the hydro/amr/particles), as well as a 
separate info file (there is a bitbucket link on the Ramses homepage if 
you want to see what the latest version of the code does in detail). The 
RHD module divides photons into "nGroups" different flux bins; for each 
bin, it writes a photon density and then a flux vector. nGroups is 
stored in the rt info file; nrtvar is written to the rt_ binary file, 
but this is (I think) a Makefile setting and not guaranteed to be 
nGroups/(1+ndim) (the user is, I believe, normally free to waste memory 
by allocating more variables than they need). For details it might be 
easiest to download the latest code and look at the code in the folder 
rt/, or ask Romain or Joki Rosdahl directly.

(Feel free to correct me if any of this is wrong!)

I agree that setting the default to the standard five (perhaps some 
boolean variables for common configurations such as metals, RHD, MHD, 
etc) and then letting users set or add their own fields by hand if they 
need to is a good approach.

On 25/11/13 16:23, Matthew Turk wrote:
> Hi all, especially RAMSES users,
>
> I'm setting up aliases to make it easier to load RAMSES datasets that
> have different field configurations.
>
> Right now, to specify a different set of fields, you have to do:
>
> pf = load( ... , fields = [ "Density", "x-velocity", ...])
>
> I am going to change this to add on different field configurations
> that can be specified with just a string.  For instance:
>
> pf = load(..., fields = "standard_five")
>
> I'm wondering what the different configurations are.  I have these two:
>
> standard_five: Density, x-velocity, y-velocity, z-velocity, Pressure
> standard_six: Density, x-velocity, y-velocity, z-velocity, Pressure, Metallicity
>
> But for MHD and RHD, what are the additional fields that should be
> added, and in what order?  And are there other common configurations
> that should be aliased?
>
> If we can come up with a set of aliases that match most use cases,
> that'd work quite well.  I'm going to issue a PR for this shortly, and
> hopefully it will make everybody's life a bit easier.
>
> -Matt
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