.. index:: fix property/atom/tracer/stream

fix property/atom/tracer/stream command
=======================================

Syntax
""""""

.. parsed-literal::

   fix id group property/atom/tracer/stream mark_step s n_tracer n insert_stream ins-ID every e

* ID, group-ID are documented in :doc:`fix <fix>` command
* property/atom/tracer/stream = style name of this fix command
* mark_step = obligatory keyword
* s = step when atoms are marked (or started to be marked, depending on marker_style)
* n_tracer = obligatory keyword
* n = number of tracer atoms to be marked
* insert_stream = obligatory keyword
* ins-ID = ID of a :doc:`fix insert/stream <fix_insert_stream>`
* every = obligatory keyword
.. parsed-literal::

   e = 'once' or integer > 0



Examples
""""""""

.. parsed-literal::

   fix tracer all property/atom/tracer/stream mark_step 10000  insert_stream ins  n_tracer 20  every 10000

Description
"""""""""""

Fix property/atom/tracer/stream marks a given number of particles (as defined
by keyword *n_tracer*) which are generated by a :doc:`fix insert/stream <fix_insert_stream>`
command (as defined by keyword *ins-ID*. The first *n_tracer* particles which pass
the insertion face after time-step *mark_step* are being marked as tracers.
In case of **every** = once, this procedure is performed once, otherwise
the procedure is repeated for the first *n_tracer* particles which pass
the insertion face after step *mark_step* + *every*.

Note that even for option *once*, particles are the marking procedure can
extend over multiple packets of insertion by a :doc:`fix insert/stream <fix_insert_stream>`
in case that the number of particles inserted in a packet is smaller than the number
of particles to tag (as defined by keyword *n_tracer*).

An arbitrary number of :doc:`fix property/atom/tracer/stream <fix_property_atom_tracer_stream>`
commands can be used for a given :doc:`fix insert/stream <fix_insert_stream>`.

It is useful to combine this command with a
:doc:`compute nparticles/tracer/region <compute_nparticles_tracer_region>`
command to compute residence time distributions.

.. warning::

   Due to some parallel operation which needed to tag the particles, you need an
   atom map to be allocated, see the :doc:`atom_modify <atom_modify>` command for details.

Restart, fix_modify, output, run start/stop, minimize info
""""""""""""""""""""""""""""""""""""""""""""""""""""""""""

Information about this fix is written to :doc:`binary restart files <restart>` .

This fix computes a per-atom vector (the marker) which can be accessed by
various :ref:`output commands <howto_8>`. .
This fix also computes a global scalar indicating how many particles were
marked since the last time the global scalar was computed. This scalar
can also be accessed by various :ref:`output commands <howto_8>`. .

Restrictions
""""""""""""


Currently, this feature does not support multi-sphere particles.

Related commands
""""""""""""""""

:doc:`compute nparticles/tracer/region <compute_nparticles_tracer_region>`

**Default:** none


.. _liws: http://www.cfdem.com
.. _ld: Manual.html
.. _lc: Section_commands.html#comm