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<CENTER><A HREF = "http://lammps.sandia.gov">LAMMPS WWW Site</A> - <A HREF = "Manual.html">LAMMPS Documentation</A> - <A HREF = "Section_commands.html#comm">LAMMPS Commands</A>
</CENTER>
<HR>
<H3>fix ave/time command
</H3>
<P><B>Syntax:</B>
</P>
<PRE>fix ID group-ID ave/time Nevery Nfreq compute-ID flag file
</PRE>
<UL><LI>ID, group-ID are documented in <A HREF = "fix.html">fix</A> command
<LI>ave/time = style name of this fix command
<LI>Nevery = calculate property every this many timesteps
<LI>Nfreq = write average property to file every this many steps
<LI>compute-ID = ID of compute that performs the calculation
<LI>flag = 0 for scalar quantity, 1 for vector quantity, 2 for both
<LI>file = filename to write results to
</UL>
<P><B>Examples:</B>
</P>
<PRE>fix 1 all ave/time 100 1000 myTemp 0 temp.stats
</PRE>
<P><B>Description:</B>
</P>
<P>Calculate one or more instantaneous quantities every few timesteps,
average them over a longer timescale, and print the results to a file.
This can be used to time-average any "compute" entity in LAMMPS such
as a temperature or pressure.
</P>
<P>The <I>compute-ID</I> specifies a <A HREF = "compute.html">compute</A> which calculates
the desired property. The compute can be previously defined in the
input script. Or it can be a compute defined by <A HREF = "thermo_style.html">thermodynamic
output</A> or other fixes such as <A HREF = "fix_nvt.html">fix
nvt</A> or <A HREF = "fix_temp_rescale.html">fix temp/rescale</A>. Users
can also write code for their own compute styles and <A HREF = "Section_modify.html">add them to
LAMMPS</A>.
</P>
<P>In all these cases, the fix ave/time style uses the global scalar or
vector calculated by the compute. See the <A HREF = "fix_ave_spatial.html">fix
ave/spatial</A> command if you wish to average
spatially, e.g. via a compute that calculates per-atom quantities.
</P>
<P>The <I>Nevery</I> and <I>Nfreq</I> arguments specify how the property will be
averaged. The property is calculated once each Nevery timesteps. It
is averaged and output every Nfreq timesteps. Nfreq must be a
multiple of Nevery. In the example above, the property is calculated
every 100 steps. After 10 calculations, the average result is written
to the file, once every 1000 steps.
</P>
<P>The <I>flag</I> argument chooses whether the scalar and/or vector
calculation of the compute is invoked. The former computes a single
global value. The latter computes N global values, where N is defined
by the compute, e.g. 6 pressure tensor components. In the vector
case, each of the N values is averaged independently and N values are
written to the file at each output.
</P>
<P>Since the calculation is performed by the compute which stores its own
"group" definition, the group specified for the fix is ignored.
LAMMPS prints a warning if the fix group and compute group do not
match.
</P>
<P>If the compute calculates pressure, it will cause the force
computations performed by LAMMPS (pair, bond, angle, etc) to calculate
virial terms each Nevery timesteps. If this is more frequent than
thermodynamic output, this adds extra cost to a simulation. However,
if a constant pressure simulation is being run (<A HREF = "fix_npt.html">fix npt</A>
or <A HREF = "fix_nph.html">fix nph</A>), LAMMPS is already calculating virial terms
for the pressure every timestep.
</P>
<P><B>Restrictions:</B> none
</P>
<P><B>Related commands:</B>
</P>
<P><A HREF = "compute.html">compute</A>, <A HREF = "fix_ave_spatial.html">fix ave/spatial</A>
</P>
<P><B>Default:</B> none
</P>
</HTML>
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