:orphan:

.. index:: compute_gas_collision_tally

.. _compute-gas-collision-tally:

.. _compute-gas-collision-tally-command:

###################################
compute gas/collision/tally command
###################################

.. _compute-gas-collision-tally-syntax:

*******
Syntax:
*******

::

   compute ID gas/collision/tally group-ID mix-ID value1 value2 ...

- ID is documented in :ref:`compute<compute>` command 

- gas/collision/tally = style name of this compute command

- group-ID = group ID for which grid cells to perform calculation on

- mix-ID = mixture ID to perform calculation on

- one or more values can be appended

- value = *id/cell* or *id1* or *id2* or *type1* or *type2* or *vx1/pre* or *vy1/pre* or *vz1/pre* or *vx2/pre* or *vy2/pre* or *vz2/pre* or *vx1/post* or *vy1/post* or *vz1/post* or *vx2/post* or *vy2/post* or *vz2/post*

::

     *id/cell* = grid cell ID
     *id1*, *id2* = particle IDs of two particles
     *type1*, *type2* = particle species of two particles
     *vx1/pre*, *vy1/pre*, *vz1/pre* = velocity components of first particle before collision
     *vx2/pre*, *vy2/pre*, *vz2/pre* = velocity components of second particle before collision
     *vx1/post*, *vy1/post*, *vz1/post* = velocity components of first particle after collision
     *vx2/post*, *vy2/post*, *vz2/post* = velocity components of second particle after collision

.. _compute-gas-collision-tally-examples:

*********
Examples:
*********

::

   compute 1 gas/collision/tally all all id id/cell time xc yc zc

This command will dump the tallies in the previous command to a dump
file every 10 steps:

::

   dump 1 tally all 10 tmp.tally c_1\[\*\]

.. _compute-gas-collision-tally-descriptio:

************
Description:
************

Tally various values for each gas-phase collision of two particles
during the current timestep.  Only gas collisions which do not result
in chemical reactions are tallied by this command.  See the related
:ref:`compute gas/reaction/tally<compute-gas-reaction-tally>` command
to tally collisions which induce reactions.  It provides different
tally value options than this compute.

Only collisions within grid cells in the grid group specified by
*group-ID* and pairs of particles with both species in the mixture
specified by *mix-ID* are included.  See the :ref:`group grid<group>`
command for info on how grid cells can be assigned to grid groups.

The results of this compute can be used by different commands in
different ways.  The values for a single timestep can be output by the
:ref:`dump tally<dump>` command.  Currently this is the only option for
accessing the tallied values.

The *id/cell* value is the ID of the grid cell in which the collision
takes place.

.. note::

  that particle IDs are generated randomly.  Thus multiple
  particles in the system can potentially have the same ID.  See
  :ref:`Section 6.17<>` for more details on particle IDs.

The *type1* and *type2* values are the integer index for the particle
species of the colliding particles.  They are values from 1 to
Nspecies. The values corresponds to the order in which species were
defined via the :ref:`species<species>` command.  See :ref:`Section 6.17<>` for more details on particle types.

The *vx1/pre*, *vy1/pre*, *vz1/pre*, *vx2/pre*, *vy2/pre*, *vz2/pre*
values are the velocity components of the two particles before the
collision.

The *vx1/post*, *vy1/post*, *vz1/post*, *vx2/post*, *vy2/post*,
*vz2/post* values are the velocity components of the two particles
after the collision.

.. _compute-gas-collision-tally-output:

************
Output info:
************

This compute calculates a per-tally array, with the number of columns
equal to the number of values.

The array can be accessed by any command that uses per-tally values
from a compute as input.  See :ref:`Section 6.4<howto-output-sparta-(stats,-dumps,>`
for an overview of SPARTA output options.

The per-tally array values will be in the :ref:`units<units>`
appropriate to the individual values as described above.  All the
velocity keywords are in velocity units.

.. _compute-gas-collision-tally-restrictio:

*************
Restrictions:
*************

none

.. _compute-gas-collision-tally-related:

*****************
Related commands:
*****************

:ref:`compute gas/reaction/tally<compute-gas-reaction-tally>`,
:ref:`compute surf/collision/tally<compute-surf-collision-tally>`,
:ref:`dump tally<dump>`

.. _compute-gas-collision-tally-default:

********
Default:
********

none