From e7d2480cbb50d9bcb25e7eeaef0392b5cbe8a0e6 Mon Sep 17 00:00:00 2001
From: Matthieu Schaller <schaller@strw.leidenuniv.nl>
Date: Sat, 3 Nov 2018 22:34:55 +0100
Subject: [PATCH] Added description of the gravity related parameters to the
RTD.
---
doc/RTD/source/ParameterFiles/index.rst | 58 ++++++++++++++++++++++++-
1 file changed, 56 insertions(+), 2 deletions(-)
diff --git a/doc/RTD/source/ParameterFiles/index.rst b/doc/RTD/source/ParameterFiles/index.rst
index 507e188b30..ae5451d71b 100644
--- a/doc/RTD/source/ParameterFiles/index.rst
+++ b/doc/RTD/source/ParameterFiles/index.rst
@@ -185,9 +185,63 @@ The behaviour of the self-gravity solver can be modifed by the parameters
provided in this section. The theory document puts these parameters into the
context of the equations being solved. We give a brief overview here.
-* The co-moving softening used for all particles :math:`\epsilon_{c}`: ``comoving_softening``
-* The
+* 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 opening angle (multipole acceptance criterion) used in the FMM :math:`\theta`: ``theta``,
+* The time-step size pre-factor :math:`\eta`: ``eta``,
+
+The time-step of a given particle is given by :math:`\Delta t =
+\eta\sqrt{\frac{\epsilon}{|\overrightarrow{a}|}}`, where
+:math:`\overrightarrow{a}` is the particle's acceleration. Power et al. (2003) recommend using :math:`\eta=0.025`.
+The last tree-related parameter is
+
+* The tree rebuild frequency: ``rebuild_frequency``.
+
+Thqe tree rebuild frequency is an optional parameter defaulting to
+:math:`0.01`. It is used to trigger the re-construction of the tree every time a
+fraction of the particles have been integrated (kicked) forward in time.
+
+Simulations using periodic boundary conditions use additional parameters for the
+Particle-Mesh part of the calculation. The last three are optional:
+
+* The number cells along each axis of the mesh :math:`N`: ``mesh_side_length``,
+* The mesh smoothing scale in units of the mesh cell-size :math:`a_{\rm
+ smooth}`: ``a_smooth`` (default: ``1.25``),
+* The scale above which the short-range forces are assumed to be 0 (in units of
+ the mesh cell-size multiplied by :math:`a_{\rm smooth}`) :math:`r_{\rm
+ cut,max}`: ``r_cut_max`` (default: ``4.5``),
+* The scale bewlo which the short-range forces are assumed to be exactly Newtonian (in units of
+ the mesh cell-size multiplied by :math:`a_{\rm smooth}`) :math:`r_{\rm
+ cut,min}`: ``r_cut_min`` (default: ``0.1``),
+
+For most runs, the default values can be used. Only the number of cells along
+each axis needs to be sepcified. The remaining three values are best described
+in the context of the full set of equations in the theory documents.
+
+As a summary, here are the values used for the EAGLE :math:`100^3~{\rm Mpc}^3`
+simulation:
+
+.. code:: YAML
+
+ # 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
+ 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
+
+
+
SPH
---
--
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