Using tangos with yt

The core of tangos is agnostic about the way in which raw simulation data is loaded and processed. The developers of tangos use pynbody for this purpose but it can be adapted for other libraries with relative ease.

As a demonstration, embryonic yt support is included.

Initial set-up: tangos+yt

Make sure you have followed the initial set up instructions. Additionally, you will need to install yt version 3.4.0 or later.

Next, download the raw simulation data. Unpack the tar file either in your home folder or the folder that you pointed the TANGOS_SIMULATION_FOLDER environment variable to.

Finally, download the tutorial_changa_yt tar. Unpack the tar file in the same folder as you unpacked tutorial_changa. The tutorial_changa_yt folder contains a series of symlinks that present the dataset with a slightly different files structure that is compatible with yt. (Specifically, yt can’t cope with the AHF files being in the same folder as the tipsy files.)

Using yt to add a simulation

At the unix command line type:

tangos add tutorial_changa_yt --handler=yt.YtInputHandler

The process should take about a minute on a standard modern computer, during which you’ll see a bunch of log messages scroll up the screen.

Let’s pick this command apart

• tangos is the command-line tool to administrate your tangos database
• add is a subcommand to add a new simulation
• tutorial_changa_yt identifies the simulation we’re adding
• --handler=yt.YtInputHandler requests that tangos uses yt as the “handler” for raw simulation and halo files.

Verify the underlying data is being read by yt

For interest, you might like to check that the data really is now being handled by yt. Open a python session and type

import tangos
tangos.get_halo("tutorial_changa_yt/%960/halo_1").load()

You should see that the returned dataset is indeed a yt object. If you previously also ran the changa+AHF tutorial with pynbody, you can also verify that

tangos.get_halo("tutorial_changa/%960/halo_1").load()

continues to return a pynbody SimSnap as before. Tangos allows simulations loaded with different libraries to coexist.

Import some AHF-defined properties

At the unix command line type:

tangos import-properties Mvir Rvir --for tutorial_changa_yt

The process should take less than a minute on a standard modern computer, during which you’ll see a bunch of log messages scroll up the screen.

The example command line lists two properties, Mvir and Rvir to import from the stat files. The added directive --for tutorial_changa_yt specifies which simulation you want to apply this operation to. It’s not strictly necessary to add this if you only have one simulation in your database.

Add some more interesting properties

Add a density profile using:

tangos write dm_density_profile --for tutorial_changa

Here,

• tangos write is the same script you called above to add properties to the database
• dm_density_profile is an array representing the dark matter density profile; to see all available properties you can call tangos list-possible-properties.

You might note that dm_density_profile is also the name of a property that can be calculated using pynbody (see the changa+AHF tutorial). Tangos is able to select the correct piece of code to work with yt instead of pynbody. For more information on how this is accomplished, see the custom output handler documentation.