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#Galaxy Analysis Toolkit

A collection of scripts and analysis tools used in my thesis research.

This also includes the text and version history of two as yet unpublished papers that were the primary research result of the code.

The code is split up into two main pieces. The galanyl “library” lives in the galanyl directory, while helper_scripts contains a number of scripts that make use of yt and galanyl to process simulation data.

#Using these scripts

First, you must download the data you would like to analyze. Right now the helper scripts are written in a such a way that they expect the full simulation dataset to be present, but they should be easily modifiable or adaptable if you only want to look at one or a few simulation outputs.

The data for Paper I are available at

The data for Paper II are available at

##Generating uniform resolution grid slabs

Note: you can skip this step if you want to download the processed data. This is only necessary if you would like to generate the processed data from the raw simulation outputs.

For example, if you would like to regenerate the processed data for the nofeedback_20pc simulation, you will need to download one or more of the simulation outputs, unzip the tarball, and place the simulation outputs in a directory named nofeedback_20pc.

Once you have downloaded the simulation outputs you would like to analyze, you need to create the needed ancillary data in two steps:

` $ python nofeedback_20pc `

This script uses yt to convert the raw simulation outputs into uniform resolution “covering grids” that the subsequent analysis scripts need. This will only generate covering grid data for the fields present in the simulation outputs. To generate the gravitational potential covering grids, you will need to do:

` $ python nofeedback_20pc `

This script needs a copy of the Enzo executable (see [here]( for information about compiling the Enzo code) since the script uses the -g option of the Enzo executable to to solve the Poisson equation.

Finally, you can run the script verify the integrity of the covering grid data after it is written to disk. This script merely checks to make sure all hdf5 files have the same internal structure, so don’t completely trust it against all possible data corruption. I created it originally to avoid errors after creating incomplete covering grid files when the generation script crashes or the filesystem hangs.

Note that if you are doing this for the full simulation dataset it will take a long time even if you are running on multiple cores. Note that both and are MPI parallelized, so you can them using e.g. mpirun on multiple cores to parallelize the analysis over multiple datasets. Note that this won’t scale very well unless you are running on a parallel filesystem since both scripts are largely IO bound.

##Generating final processed data

Finally, to generate the final processed data, including maps of surface densities, velocity dispersions, and Toomre Q parameters, you should use the script. This script uses the covering grid data generated in the previous step to create GalaxyAnalyzer objects – the main analysis class provided by the galaxy analysis toolkit. The GalaxyAnalyzer class offers a number of analysis options to process a subset of the abailable data but also offers an interface to calculate all the derived data that it knows how to calculate. This is the interface that uses. The script can be easily modified to only calculate a subset of the data if you do not want all of the processed data. To run the script, simply do:

` $ python `

Like the covering grid generators, this script is also MPI-parallel, so run it with mpirun to speed up the analysis. This script is also largely IO-bound, so you will liekly not see a very good scaling unless you are running on a parallel filesystem.

Note also that some of the expensive calculations are parallelized using OpenMP so long as your operating system and compiler supports it. Right now, that means you will need gcc although supposedly LLVM/Clang is also getting OpenMP support soon. I optimized to iterate over the data on a single node, using MPI parallelism to iterate over the datasets, but breaking up the work necessary to process a given dataset using OpenMP. As a rule of thumb, I used a node with 16 cores and used 4 MPI tasks, so each MPI task used 4 OpenMP threads in the OpenMP-parallelized sections of the analysis.

#Loading and working with the data

The available data can be accessed via an open-source python analysis environment. The raw simulation data are written to disk in Enzo’s HDF5-based data format. The processed data are written to disk in a directory structure containing many simple hdf5 files that contain a single dataset.

##Simulation outputs

For the raw simulation outputs, the recommended way to load them for analysis and visualization is using yt. You will need to install yt using either the installation script, conda, or pip, depending on whether you have a python environment set up and how you set it up. See for more details.

Once you have yt installed, download one of the raw datasets, unzip it, and then load it:

` $ wget $ tar xzvf DD0600.tar.gz $ python >>> import yt >>> ds = yt.load('DD0600/DD0600') `

You can then pass the ds object to yt’s plotting commands or access yt data objects through it to get at any on-disk or derived fields.

##Processed Data

The easiest way to deal with the processed data is via the galaxy analysis toolkit. This can be installed via pip or from the source code. To install via pip:

$ pip install galanyl

To install from the source code:

` $ hg clone $ cd galaxy_analysis $ python develop `

Note that the latter version will make the source code the “live” version that the python interpreter imports, so edits there will be immediately available the next time you import the toolkit.

To load one of the example datasets, you will need to download it, unzip it, and then load it in memory:

` $ wget $ tar xzvf DD0600_toomre.tar.gz $ python >>> from galanyl import GalaxyAnalyzer >>> from matplotlib import pyplot as plt >>> g = GalaxyAnalyzer.from_hdf5_file('DD0600_toomre') >>> print g.gas.surface_density >>> print g.stars.velocity_dispersion >>> plt.imshow(g.gas.total_toome_q) `

All of the data will be available via attributes of the GalaxyAnalyzer instance, as in the above example. All quantities are in CGS units. The easiest way to explore the various attributes of these objects is via tab completion in IPython or by reading the GalaxyAnalyzer source code.

Alternatively, the data are also split up into one hdf5 file per dataset, so any hdf5 reader should be able to access the data without going through GalaxyAnalyzer.

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