diff --git a/doc/RTD/source/ParameterFiles/index.rst b/doc/RTD/source/ParameterFiles/index.rst index ec938c6062056e1c1e081c10813ed61b8bfc936f..f87045797d8846a327066fcd3dc52c1eb5ff10fb 100644 --- a/doc/RTD/source/ParameterFiles/index.rst +++ b/doc/RTD/source/ParameterFiles/index.rst @@ -72,11 +72,11 @@ section. A list of all the possible parameters is kept in the file Internal Unit System -------------------- -This section describes the units used internally by the code. This is -the system of units in which all the equations are solved. All -physical constants are converted to this system and if the ICs use a -different system (see :ref:`ICs_units_label`) the particle quantities -will be converted when read in. +The ``InternalUnitSystem`` section describes the units used internally by the +code. This is the system of units in which all the equations are solved. All +physical constants are converted to this system and if the ICs use a different +system (see :ref:`ICs_units_label`) the particle quantities will be converted +when read in. The system of units is described using the value of the 5 basic units of any system with respect to the CGS system. Instead of using a unit @@ -132,7 +132,7 @@ exercise for the reader [#f1]_. Cosmology --------- -When running a cosmological simulation, this section set the values of the +When running a cosmological simulation, the section ``Cosmology`` sets the values of the cosmological model. The epanded :math:`\Lambda\rm{CDM}` parameters governing the background evolution of the Univese need to be specified here. These are: @@ -186,7 +186,7 @@ Gravity ------- 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 +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``, @@ -251,10 +251,64 @@ SPH Time Integration ---------------- +The ``TimeIntegration`` section is used to set some general parameters related to time +integration. In all cases, users have to provide a minimal and maximal time-step +size: + +* Maximal time-step size: ``dt_max`` +* Minimal time-step size: ``dt_min`` + +These quantities are expressed in internal units. All particles will have their +time-step limited by the maximal value on top of all the other criteria that may +apply to them (gravity acceleration, Courant condition, etc.). If a particle +demands a time-step size smaller than the minimum, SWIFT will abort with an +error message. This is a safe-guard against simulations that would never +complete due to the number of steps to run being too large. + +When running a non-cosmological simulation, the user also has to provide the +time of the start and the time of the end of the simulation: + +* Start time: ``time_begin`` +* End time: ``time_end`` + +Both are expressed in internal units. The start time is typically set to ``0`` +but SWIFT can handle any value here. For cosmological runs, these values are +ignored and the start- and end-points of the runs are specified by the start and +end scale-factors in the cosmology section of the parameter file. + +Additionally, when running a cosmological volume, advanced users can specify the +value of the dimensionless pre-factor entering the time-step condition linked +with the motion of particles with respect to the background expansion and mesh +size. See the theory document for the exact equations. + +* Dimensionless pre-factor of the maximal allowed displacement: + ``max_dt_RMS_factor`` (default: ``0.25``) + +This value rarely needs altering. + +A full time-step section for a non-cosmological run would be: + +.. code:: YAML + + TimeIntegration: + time_begin: 0 # Start time in internal units. + time_end: 10. # End time in internal units. + dt_max: 1e-2 + dt_min: 1e-6 + +Whilst for a cosmological run, one would need: + +.. code:: YAML + + TimeIntegration: + dt_max: 1e-4 + dt_min: 1e-10 + max_dt_RMS_factor: 0.25 # Default optional value + Initial Conditions ------------------ -This section of the parameter file contains all the options related to +This ``IntialConditions`` section of the parameter file contains all the options related to the initial conditions. The main two parameters are * The name of the initial conditions file: ``file_name``, @@ -306,9 +360,9 @@ be: InitialConditions: file_name: my_ics.hdf5 periodic: 1 - cleanup_h_factors: 1 - cleanup_velocity_factors: 1 - generate_gas_in_ics: 1 + cleanup_h_factors: 1 + cleanup_velocity_factors: 1 + generate_gas_in_ics: 1 cleanup_smoothing_lengths: 1 @@ -352,7 +406,7 @@ Restarts -------- SWIFT can write check-pointing files and restart from them. The behaviour of -this mechanism is driven by the options int he `Restarts` section of the YAML +this mechanism is driven by the options in the ``Restarts`` section of the YAML parameter file. All the parameters are optional but default to values that ensure a reasonable behaviour.