# GEAR RT¶

Warning

The radiative transfer schemes are still in development and are not useable at this moment. This page is currently a placeholder to document new features and requirements as the code grows.

## Compiling for GEAR RT¶

To compile swift to be able to run with GEAR RT, you need to configure with --with-rt=GEAR_N where N is the integer number of photon groups that you intend to use in your simulation.

## Runtime Parameters¶

You need to provide the following runtime parameters in the yaml file:

GEARRT:
photon_groups_Hz: [3.288e15, 5.945e15, 13.157e15]  # Photon frequency group bin edges in Hz
use_const_emission_rates: 1
star_emission_rates_LSol: [1., 1., 1., 1.]         # stellar emission rates for each photon
# frequency bin in units of solar luminosity


The photon_groups need to be N - 1 frequency edges (floats) to separate the spectrum into N groups. The outer limits of zero and infinity are assumed.

At the moment, the only way to define star emission rates is to use constant star emission rates that need to be provided in the parameter file. The star emission rates need to be defined for each photon frequency group individually. The first entry of the array is for the photon group with frequency [0, <first entry of photon_groups_Hz>). Each star particle will then emit the given energies, independent of their other properties. Furthermore, even though the parameter use_const_emission_rates is intended to be optional in the future, for now it needs to be set to 1.

## Initial Conditions¶

Optionally, you may want to provide initial conditions for the radiation field. To do so, you need to add the following datasets to the /PartType0 particle group:

PhotonEnergiesGroup1
PhotonEnergiesGroup2
.
.
.
PhotonEnergiesGroupN
PhotonFluxesGroup1
PhotonFluxesGroup2
.
.
.
PhotonFluxesGroupN


The PhotonEnergiesX datasets need to have dimension nparts, while the PhotonFluxesGroupX datasets need to have dimension (nparts, 3), where nparts is the number of hydro particles.