@@ -49,14 +49,32 @@ final time is specified in the list.
Output Selection
~~~~~~~~~~~~~~~~
With SWIFT, you can select the particle fields to output in snapshot
using the parameter file. In section ``SelectOutput``, you can remove
a field by adding a parameter formatted in the following way
``field_parttype`` where ``field`` is the name of the field that you
want to remove (e.g. ``Masses``) and ``parttype`` is the type of
particles that contains this field (e.g. ``Gas``, ``DM`` or ``Star``).
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
Users can generate a ``yaml`` file containing all the possible fields
available for a given configuration of SWIFT by running
``./swift --output-params output.yml`` or equivalently ``./swift -o
output.yml``. The file generated contains the list of fields that a
simulation running with this config would output in each snapshot. It
also lists the description string of each field and the unit
conversion string to go from internal comoving units to physical
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
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@@ -64,10 +82,12 @@ 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 this::
parameter file would look like:
.. code:: YAML
SelectOutput:
Masses_DM: 0
You can generate a ``yaml`` file containing all the possible fields
available for a given configuration of SWIFT by running ``./swift --output-params output.yml``.
Entries can simply be copied from the ``output.yml`` generated by the
time_first:0.# (Optional) Time of the first output if non-cosmological time-integration (in internal units)
delta_time:0.01# Time difference between consecutive outputs (in internal units)
invoke_stf:0# (Optional) Call VELOCIraptor every time a snapshot is written irrespective of the VELOCIraptor output strategy.
compression:0# (Optional) Set the level of compression of the HDF5 datasets [0-9]. 0 does no compression.
compression:0# (Optional) Set the level of GZIP compression of the HDF5 datasets [0-9]. 0 does no compression. The lossless compression is applied to *all* the fields.
distributed:0# (Optional) When running over MPI, should each rank write a partial snapshot or do we want a single file? 1 implies one file per MPI rank.
int_time_label_on:0# (Optional) Enable to label the snapshots using the time rounded to an integer (in internal units)
UnitMass_in_cgs:1# (Optional) Unit system for the outputs (Grams)