:orphan:

.. index:: compute_surf_collision_tally

.. _compute-surf-collision-tally:

.. _compute-surf-collision-tally-command:

####################################
compute surf/collision/tally command
####################################

.. _compute-surf-collision-tally-syntax:

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

::

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

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

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

- group-ID = group ID for which surface elements to perform calculation on

- mix-ID = mixture ID to perform calculation on

- one or more values can be appended

- value = *id/surf* or *id* or *type* or *time* or *xc* or *yc* or *zc* or *vx/pre* or *vy/pre* or *vz/pre* or *vx/post* or *vy/post* or *vz/post*

::

     *id/surf* = surface element ID
     *id* = particle ID
     *type* = particle species
     *time* = time of collision (within timestep, see below)
     *xc*, *yc*, *zc* = coordinates of collision point
     *vx/pre*, *vy/pre*, *vz/pre* = velocity components before collision
     *vx/post*, *vy/post*, *vz/post* = velocity components after collision

.. _compute-surf-collision-tally-examples:

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

::

   compute 1 surf/collision/tally all all id id/surf 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-surf-collision-tally-descriptio:

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

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

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

This compute can be used for simulations with either explicit or
implicit surface elements.  See :ref:`Section 6.13<>` for
more discussion of explicit and implicit surfaces.

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/surf* value is the ID of the surface element.  For explicit
surfaces, surface element IDs are unique.  For implicit surfaces, the
surface ID of all the surface elements within a grid cell are the grid
cell ID.  See :ref:`Section 6.13<>` for more discussion of
explicit and implicit surfaces.

.. 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 *type* value is an integer index for the particle species.  It is
a value from 1 to Nspecies. The value 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 *time* value is the point in time within the timestep when the
collision occured.  Thus if the timestep size is DT, as set by the
:ref:`timestep<timestep>` command, the *time* values will all be within
the range of 0.0 to DT, for all collisions tallied by this compute on
each timestep it is invoked.

The *xc*, *yc*, and *zc* are the coordinates of the collision point
between the particle and the surface element.

The *vx/pre*, *vy/pre*, *vz/pre* values are the velocity components of
the incident particle before it collides with the surface element.

The *vx/post*, *vy/post*, *vz/post* values are the velocity components
of the particle after it collides with the surface element.

.. _compute-surf-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.  *Time* is in
time units; see above for details.  *Xc*, *yc*, and *zc* are in
distance units.  *Vx/pre*, *vy/pre*, *vz/pre* are in velocity units, as
are *vx/post*, *vy/post*, *vz/post*.

.. _compute-surf-collision-tally-restrictio:

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

none

.. _compute-surf-collision-tally-related:

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

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

.. _compute-surf-collision-tally-default:

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

none