# fix property/atom/tracer/stream command

## Syntax

    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 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 fix insert/stream
- every = obligatory keyword

    e = 'once' or integer > 0

## Examples

    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 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 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 fix property/atom/tracer/stream commands can be used for a given fix insert/stream.

It is useful to combine this command with a 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 atom_modify command for details.

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

Information about this fix is written to binary restart files .

This fix computes a per-atom vector (the marker) which can be accessed by various output commands. . 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 output commands. .

## Restrictions

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

## Related commands

compute nparticles/tracer/region

Default: none