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<HTML>
<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 lb/momentum command
</H3>
<P><B>Syntax:</B>
</P>
<PRE>fix ID group-ID lb/momentum nevery keyword values ...
</PRE>
<UL><LI>ID, group-ID are documented in the <A HREF = "fix.html">fix</A> command
<LI>lb/momentum = style name of this fix command
<LI>nevery = adjust the momentum every this many timesteps
<LI>zero or more keyword/value pairs may be appended
<LI>keyword = <I>linear</I>
<PRE> <I>linear</I> values = xflag yflag zflag
xflag,yflag,zflag = 0/1 to exclude/include each dimension.
</PRE>
</UL>
<P><B>Examples:</B>
</P>
<PRE>fix 1 sphere lb/momentum
fix 1 all lb/momentum linear 1 1 0
</PRE>
<P><B>Description:</B>
</P>
<P>This fix is based on the <A HREF = "fix_momentum.html">fix momentum</A> command, and
was created to be used in place of that command, when a
lattice-Boltzmann fluid is present.
</P>
<P>Zero the total linear momentum of the system, including both the atoms
specified by group-ID and the lattice-Boltzmann fluid every nevery
timesteps. This is accomplished by adjusting the particle velocities
and the fluid velocities at each lattice site.
</P>
<P>NOTE: This fix only considers the linear momentum of the system.
</P>
<P>By default, the subtraction is performed for each dimension. This can
be changed by specifying the keyword <I>linear</I>, along with a set of
three flags set to 0/1 in order to exclude/ include the corresponding
dimension.
</P>
<P><B>Restart, fix_modify, output, run start/stop, minimize info:</B>
</P>
<P>No information about this fix is written to <A HREF = "restart.html">binary restart
files</A>. None of the <A HREF = "fix_modify.html">fix_modify</A> options
are relevant to this fix. No global or per-atom quantities are stored
by this fix for access by various <A HREF = "Section_howto.html#4_15">output
commands</A>. No parameter of this fix can be
used with the <I>start/stop</I> keywords of the <A HREF = "run.html">run</A> command.
This fix is not invoked during <A HREF = "minimize.html">energy minimization</A>.
</P>
<P><B>Restrictions:</B>
</P>
<P>Can only be used if a lattice-Boltzmann fluid has been created via the
<A HREF = "fix_lb_fluid.html">fix lb/fluid</A> command, and must come after this
command.
</P>
<P>This fix is part of the USER-LB package. It is only enabled if LAMMPS
was built with that package. See the <A HREF = "Section_start.html#start_3">Making
LAMMPS</A> section for more info.
</P>
<P><B>Related commands:</B>
</P>
<P><A HREF = "fix_momentum.html">fix momentum</A>, <A HREF = "fix_lb_fluid.html">fix lb/fluid</A>
</P>
<P><B>Default:</B>
</P>
<P>Zeros the total system linear momentum in each dimension.
</P>
</HTML>
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