Example data

swiftgalaxy comes with utilities to generate some schematic example data on the fly, and to download some more realistic example datasets. This is implemented via two helper objects in the demo_data module, generated_examples and web_examples. You can view the available example data sets with:

from swiftgalaxy.demo_data import generated_examples, web_examples

print(generated_examples)
print(web_examples)

Each example can be accessed as an attribute, for example generated_examples.snapshot creates an example snapshot file. The helper class is set up so that the path to the example file(s) is returned when the attribute is accessed. This means that we can pass the examples directly to swiftgalaxy classes that expect file paths as arguments - the needed input files will be created/downloaded (unless they already exist) and their location passed automatically. The example data is stored in a directory demo_data/ in the current working directory, and this directory is created if it does not exist.

The example data generated on the fly is very simplistic: the snapshot consists of a cubic volume with uniform randomly distributed dark matter and gas particles. Two “galaxies” are superimposed on this by placing additional particles forming a sphere of dark matter and a disc of stars and gas for each. The halo catalogue examples contain two objects (the two galaxies) but their properties are mostly written in “by hand” rather than calculated from the particle distributions. These examples are useful for demonstrating or verifying the functionality of swiftgalaxy, but not much more.

The example data available for download (about 700 MB for the entire set) is more realistic. The sample snapshot is taken from a run of the EAGLE_6 example simulation included with SWIFT. The halo catalogues come from running Velociraptor, SOAP (with HBT-Herons backend) and Caesar on the snapshot.

Usage

The following code snippets set up a SWIFTGalaxy object with example data generated on the fly:

# a synthetically created snapshot with a minimalist implementation of a halo catalogue

from swiftgalaxy import SWIFTGalaxy
from swiftgalaxy.demo_data import generated_examples, ToyHF

SWIFTGalaxy(
    generated_examples.snapshot,
    ToyHF(index=0),
)

# a synthetically created snapshot with a synthetically created SOAP catalogue

from swiftgalaxy.demo_data import generated_examples
from swiftgalaxy import SWIFTGalaxy, SOAP

SWIFTGalaxy(
    generated_examples.virtual_snapshot,  # notice virtual_snapshot, not snapshot
    SOAP(generated_examples.soap, soap_index=0),
)

# a synthetically created snapshot with a synthetically created Velociraptor catalogue

from swiftgalaxy.demo_data import generated_examples
from swiftgalaxy import SWIFTGalaxy, Velociraptor

SWIFTGalaxy(
    generated_examples.snapshot,
    Velociraptor(generated_examples.velociraptor, halo_index=0),
)

# a synthetically created snapshot with a synthetically created Caesar catalogue

from swiftgalaxy.demo_data import generated_examples
from swiftgalaxy import SWIFTGalaxy, Caesar

SWIFTGalaxy(
    generated_examples.snapshot,
    Caesar(generated_examples.caesar, group_type="galaxy", group_index=0),
    # can also use group_type="halo"
)

The following code snippets set up a SWIFTGalaxy object with downloaded example data:

# a small EAGLE snapshot with a SOAP catalogue

from swiftgalaxy.demo_data import web_examples
from swiftgalaxy import SWIFTGalaxy, SOAP

SWIFTGalaxy(
    web_examples.virtual_snapshot,  # notice virtual_snapshot, not snapshot
    SOAP(web_examples.soap, soap_index=0),
)

# a small EAGLE snapshot with a Velociraptor catalogue

from swiftgalaxy.demo_data import web_examples
from swiftgalaxy import SWIFTGalaxy, Velociraptor

SWIFTGalaxy(
    web_examples.snapshot,
    Velociraptor(web_examples.velociraptor, halo_index=0),
)

# a small EAGLE snapshot with a Caesar catalogue

from swiftgalaxy.demo_data import web_examples
from swiftgalaxy import SWIFTGalaxy, Caesar

SWIFTGalaxy(
    web_examples.snapshot,
    Caesar(web_examples.caesar, group_type="galaxy", group_index=0),
    # can also use group_type="halo"
)

The example data can be removed with generated_examples.remove() and web_examples.remove().