@@ -60,34 +60,89 @@ CGS. Entries in the file look like:
...
@@ -60,34 +60,89 @@ CGS. Entries in the file look like:
.. code:: YAML
.. code:: YAML
SelectOutput:
Default:
# Particle Type Gas
# Particle Type Gas
Coordinates_Gas: 1 # Co-moving positions of the particles. ::: Conversion to physical CGS: a U_L [ cm ]
Coordinates_Gas: off # Co-moving positions of the particles : 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 ]
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: 1 # Masses of the particles. ::: Conversion to physical CGS: U_M [ g ]
Masses_Gas: on # Masses of the particles : 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 ]
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 the
YAML parameter file. In section ``SelectOutput``, users can demand to
Users can select the particle fields to output in snapshot using a (separate)
remove a field by adding a parameter formatted in the following way
YAML parameter file. By default, you can define a section `Default` at the
``field_parttype`` where ``field`` is the name of the field that is to
top level of this file (in the exact same way as the file dumped by using the
be removed (e.g. ``Masses``) and ``parttype`` is the type of particles
`-o` option in SWIFT). By default, all fields are written, but by using the
that contains this field (``Gas``, ``DM``, ``Stars`` or ``BH``). For
"off" string, you can force the code to skip over unwanted outputs.
a parameter, the only values accepted are ``0`` (skip this field when
writing) or ``1`` (default, do not skip this field when writing). By
You must then, in the regular SWIFT parameter file, select the following
default all fields are written.
options:
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:
.. code:: YAML
.. code:: YAML
SelectOutput:
Snapshots:
Masses_DM: 0
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
Entries can simply be copied from the ``output.yml`` generated by the
``-o`` runtime flag.
``-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
labelled as ``Snipshot``. The name of the output selection that corresponds
to your choice in the output list will be written to the snapshot header as
