@@ -191,12 +191,32 @@ The behaviour of the self-gravity solver can be modified by the parameters
provided in the ``Gravity`` section. The theory document puts these parameters into the
context of the equations being solved. We give a brief overview here.
* The Plummer-equivalent co-moving softening length used for all particles :math:`\epsilon_{com}`: ``comoving_softening``,
* The Plummer-equivalent maximal physical softening length used for all particles :math:`\epsilon_{max}`: ``comoving_softening``,
At any redshift :math:`z`, the Plummer-equivalent softening length used by the
code will be :math:`\epsilon=\min(\epsilon_{max},
\frac{\epsilon_{com}}{z+1})`. This is expressed in internal units.
* The Plummer-equivalent co-moving softening length used for all dark matter particles :math:`\epsilon_{\rm com,DM}`: ``comoving_DM_softening``,
* The Plummer-equivalent co-moving softening length used for all baryon particles (gas, stars, BHs) :math:`\epsilon_{\rm com,bar}`: ``comoving_baryon_softening``,
* The Plummer-equivalent maximal physical softening length used for all dark matter particles :math:`\epsilon_{\rm max,DM}`: ``max_physical_DM_softening``,
* The Plummer-equivalent maximal physical softening length used for all baryon particles (gas, stars, BHs) :math:`\epsilon_{\rm max,bar}`: ``max_physical_baryon_softening``,
At any redshift :math:`z`, the Plummer-equivalent softening length used by
the code will be :math:`\epsilon=\min(\epsilon_{max},
\frac{\epsilon_{com}}{z+1})`. The same calculation is performed
independently for the dark matter and baryon particles. All the softening
quantities are expressed in internal units. Calculations that only involve
DM or baryons can leave the unused quantities out of the parameter
file. For non-cosmological runs, only the physical softening lengths need
to be supplied.
In case of zoom simulations, the softening of the additional, more massive, background
particles is specified via the parameter
``softening_ratio_background``. Since these particles will typically have
different masses to degrade the resolution away from the zoom region, the
particles won't have a single softening value. Instead, we specify the
fraction of the mean inter-particle separation to use. The code will then
derive the softening length of each particle assuming the mean density of
the Universe. That is :math:`\epsilon_{\rm background} =
f\sqrt[3]{\frac{m}{\Omega_m\rho_{\rm crit}}}`, where :math:`f` is the
user-defined value (typically of order 0.05).
The accuracy of the gravity calculation is governed by the following two parameters:
* The opening angle (multipole acceptance criterion) used in the FMM :math:`\theta`: ``theta``,
* The time-step size pre-factor :math:`\eta`: ``eta``,
...
...
@@ -236,15 +256,17 @@ simulation:
# Parameters for the self-gravity scheme for the EAGLE-100 box
Gravity:
eta: 0.025
theta: 0.7
comoving_softening: 0.0026994 # 0.7 proper kpc at z=2.8.
max_physical_softening: 0.0007 # 0.7 proper kpc
rebuild_frequency: 0.01 # Default optional value
eta: 0.025
theta: 0.7
mesh_side_length: 512
a_smooth: 1.25 # Default optional value
r_cut_max: 4.5 # Default optional value
r_cut_min: 0.1 # Default optional value
comoving_DM_softening: 0.0026994 # 0.7 proper kpc at z=2.8.
