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fix lb/momentum command :h3

[Syntax:]

fix ID group-ID lb/momentum nevery keyword values ... :pre

ID, group-ID are documented in the "fix"_fix.html command :ulb,l
lb/momentum = style name of this fix command :l
nevery = adjust the momentum every this many timesteps :l
zero or more keyword/value pairs may be appended :l
keyword = {linear} :l
  {linear} values = xflag yflag zflag
    xflag,yflag,zflag = 0/1 to exclude/include each dimension. :pre
:ule

[Examples:]

fix 1 sphere lb/momentum
fix 1 all lb/momentum linear 1 1 0 :pre

[Description:]

This fix is based on the "fix momentum"_fix_momentum.html command, and
was created to be used in place of that command, when a
lattice-Boltzmann fluid is present.

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.

NOTE:  This fix only considers the linear momentum of the system.

By default, the subtraction is performed for each dimension.  This can
be changed by specifying the keyword {linear}, along with a set of
three flags set to 0/1 in order to exclude/ include the corresponding
dimension.

[Restart, fix_modify, output, run start/stop, minimize info:]

No information about this fix is written to "binary restart
files"_restart.html.  None of the "fix_modify"_fix_modify.html options
are relevant to this fix.  No global or per-atom quantities are stored
by this fix for access by various "output commands"_Howto_output.html.
No parameter of this fix can be used with the {start/stop} keywords of
the "run"_run.html command.  This fix is not invoked during "energy
minimization"_minimize.html.

[Restrictions:]

Can only be used if a lattice-Boltzmann fluid has been created via the
"fix lb/fluid"_fix_lb_fluid.html command, and must come after this
command.

This fix is part of the USER-LB package.  It is only enabled if LAMMPS
was built with that package.  See the "Build
package"_Build_package.html doc page for more info.

[Related commands:]

"fix momentum"_fix_momentum.html, "fix lb/fluid"_fix_lb_fluid.html

[Default:]

Zeros the total system linear momentum in each dimension.
