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

[Sam Geen]

Yes and no. NVAR must be big enough, but it can be bigger than necessary 
(I think); it's a Makefile setting when compiling Ramses. You can 
guarantee that the first 4 variables are the same, but after that I 
suspect the best approach is to use boolean flags to specify whether the 
run contains MHD, RHD, metals, etc. Normally it's a good guess that 5 is 
pressure and 6 (if it exists) is metals, but as I said it seems like MHD 
puts the B-field before pressure and metallicity.

On 25/11/13 17:36, Nathan Goldbaum wrote:
> Does that mean that it should be possible to infer the field list from 
> NVAR alone?
>
>
> On Mon, Nov 25, 2013 at 8:29 AM, Sam Geen <samgeen at astro.ox.ac.uk 
> <mailto:samgeen at astro.ox.ac.uk>> wrote:
>
>     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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