@@ -60,34 +60,86 @@ CGS. Entries in the file look like:
.. code:: YAML
SelectOutput:
# Particle Type Gas
Coordinates_Gas: 1 # Co-moving positions of the particles. ::: Conversion to physical CGS: a U_L [ cm ]
Velocities_Gas: 1 # Peculiar velocities of the stars. This is (a * dx/dt) where x is the co-moving positions of the particles. ::: Conversion to physical CGS: U_L U_t^-1 [ cm s^-1 ]
Masses_Gas: 1 # Masses of the particles. ::: Conversion to physical CGS: U_M [ g ]
SmoothingLengths_Gas: 1 # Co-moving smoothing lengths (FWHM of the kernel) of the particles. ::: Conversion to physical CGS: a U_L [ cm ]
Users can select the particle fields to output in snapshot using the
YAML parameter file. In section ``SelectOutput``, users can demand to
remove a field by adding a parameter formatted in the following way
``field_parttype`` where ``field`` is the name of the field that is to
be removed (e.g. ``Masses``) and ``parttype`` is the type of particles
that contains this field (``Gas``, ``DM``, ``Stars`` or ``BH``). For
a parameter, the only values accepted are ``0`` (skip this field when
writing) or ``1`` (default, do not skip this field when writing). By
default all fields are written.
This field is mostly used to remove unnecessary output by listing them
with 0's. A classic use-case for this feature is a DM-only simulation
(pure n-body) where all particles have the same mass. Outputting the
mass field in the snapshots results in extra i/o time and unnecessary
waste of disk space. The corresponding section of the ``yaml``
parameter file would look like:
Default:
# Particle Type Gas
Coordinates_Gas: off # Co-moving positions of the particles : a U_L [ cm ]
Velocities_Gas: on # Peculiar velocities of the stars. This is (a * dx/dt) where x is the co-moving positions of the particles : U_L U_t^-1 [ cm s^-1 ]
Masses_Gas: on # Masses of the particles : U_M [ g ]
SmoothingLengths_Gas: on # Co-moving smoothing lengths (FWHM of the kernel) of the particles : a U_L [ cm ]
...
Users can select the particle fields to output in snapshot using a (separate)
YAML parameter file. By default, you can define a section `Default` at the
top level of this file (in the exact same way as the file dumped by using the
`-o` option in SWIFT). By default, all fields are written, but by using the
"off" string, you can force the code to skip over unwanted outputs.
You must then, in the regular SWIFT parameter file, select the following
options:
.. code:: YAML
SelectOutput:
Masses_DM: 0
Snapshots:
select_output_on: 1
select_output: your_select_output_yaml.yml
This field is mostly used to remove unnecessary output by listing them with
0's. A classic use-case for this feature is a DM-only simulation (pure
n-body) where all particles have the same mass. Outputting the mass field in
the snapshots results in extra i/o time and unnecessary waste of disk space.
The corresponding section of the YAML file would look like:
.. code:: YAML
Default:
Masses_DM: off
Entries can simply be copied from the ``output.yml`` generated by the
``-o`` runtime flag.
Combining Output Lists and Output Selection
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
It is possible to combine the behaviour of the output list and the select
output file. To do so, you will need to enable both the ``select_output`` and
``output_list`` options in your main ``parameter_file.yml`` as follows:
.. code:: YAML
Snapshots:
output_list_on: 1
output_list: "output_list.txt"
select_output_on: 1
select_output: "select_output.yml"
A typical use case for such a scenario is the dumping of 'snapshots' and
so-called 'snipshots', containing less information than their full snapshot
cousins. To do this, we will define two top-level sections in our
``select_output.yml`` file as follows:
.. code:: YAML
# Only turn off DM masses in snapshots, everything else is turned on
Snapshot:
Masses_DM: off
# Turn off lots of stuff in snipshots!
Snipshot:
Metal_Mass_Fractions_Gas: off
Element_Mass_Fractions_Gas: off
...
To then select which outputs are 'snapshots' and which are 'snipshots', you
will need to add the ``Select Output`` column to the ``output_list.txt`` as
follows::
# Redshift, Select Output
100.0, Snapshot
90.0, Snipshot
80.0, Snipshot
70.0, Snipshot
60.0, Snapshot
...
This will enable your simulation to perform partial dumps only at the outputs
