<li>zero or more keyword/arg pairs may be appended</li>
<li>keyword = <em>region</em> or <em>norm</em> or <em>units</em> or <em>ave</em> or <em>file</em> or <em>overwrite</em> or <em>title1</em> or <em>title2</em> or <em>title3</em></li>
</ul>
<preclass="literal-block">
<em>region</em> arg = region-ID
region-ID = ID of region atoms must be in to contribute to spatial averaging
<em>norm</em> arg = <em>all</em> or <em>sample</em>
<em>units</em> arg = <em>box</em> or <em>lattice</em> or <em>reduced</em>
<em>ave</em> args = <em>one</em> or <em>running</em> or <em>window M</em>
one = output new average value every Nfreq steps
running = output cumulative average of all previous Nfreq steps
window M = output average of M most recent Nfreq steps
<em>file</em> arg = filename
filename = file to write results to
<em>overwrite</em> arg = none = overwrite output file with only latest output
<p>Use one or more per-atom vectors as inputs every few timesteps, bin
their values spatially into spherical shells based on current atom
coordinates, and average the bin values over longer timescales. The
resulting bin averages can be used by other <aclass="reference internal"href="Section_howto.html#howto-15"><spanclass="std std-ref">output commands</span></a> such as <aclass="reference internal"href="thermo_style.html"><spanclass="doc">thermo_style custom</span></a>, and can also be written to a file.</p>
<p>The group specified with the command means only atoms within the group
contribute to bin averages. If the <em>region</em> keyword is used, the atom
must be in both the group and the specified geometric
<aclass="reference internal"href="region.html"><spanclass="doc">region</span></a> in order to contribute to bin averages.</p>
<p>Each listed value can be an atom attribute (position, velocity, force
component), a mass or number density, or the result of a
<aclass="reference internal"href="compute.html"><spanclass="doc">compute</span></a> or <aclass="reference internal"href="fix.html"><spanclass="doc">fix</span></a> or the evaluation of an
atom-style <aclass="reference internal"href="variable.html"><spanclass="doc">variable</span></a>. In the latter cases, the
compute, fix, or variable must produce a per-atom quantity, not a
global quantity. If you wish to time-average global quantities from a
compute, fix, or variable, then see the <aclass="reference internal"href="fix_ave_time.html"><spanclass="doc">fix ave/time</span></a> command.</p>
<p><aclass="reference internal"href="compute.html"><spanclass="doc">Computes</span></a> that produce per-atom quantities are those
which have the word <em>atom</em> in their style name. See the doc pages for
individual <aclass="reference internal"href="fix.html"><spanclass="doc">fixes</span></a> to determine which ones produce per-atom
quantities. <aclass="reference internal"href="variable.html"><spanclass="doc">Variables</span></a> of style <em>atom</em> are the only
ones that can be used with this fix since all other styles of variable
produce global quantities.</p>
<p>The per-atom values of each input vector are binned and averaged
independently of the per-atom values in other input vectors.</p>
<p><em>Nbins</em> specifies the number of spherical shells which will be created
between r_min and r_max centered at (origin_x, origin_y, origin_z).</p>
<divclass="admonition note">
<pclass="first admonition-title">Note</p>
<pclass="last">This fix works by creating an array of size Nbins by Nvalues on
each processor. Nbins is the total number of bins; Nvalues is the
number of input values specified. Each processor loops over its
atoms, tallying its values to the appropriate bin. Then the entire
array is summed across all processors. This means that using a large
number of bins will incur an overhead in memory and computational cost
(summing across processors), so be careful to use reasonable numbers
of bins.</p>
</div>
<hrclass="docutils"/>
<p>The <em>Nevery</em>, <em>Nrepeat</em>, and <em>Nfreq</em> arguments specify on what
timesteps the input values will be used to bin them and contribute to
the average. The final averaged quantities are generated on timesteps
that are a multiples of <em>Nfreq</em>. The average is over <em>Nrepeat</em>
quantities, computed in the preceding portion of the simulation every
<em>Nevery</em> timesteps. <em>Nfreq</em> must be a multiple of <em>Nevery</em> and
<em>Nevery</em> must be non-zero even if <em>Nrepeat</em> is 1.
Also, the timesteps
contributing to the average value cannot overlap,
i.e. Nrepeat*Nevery can not exceed Nfreq.</p>
<p>For example, if Nevery=2, Nrepeat=6, and Nfreq=100, then values on
timesteps 90,92,94,96,98,100 will be used to compute the final average
on timestep 100. Similarly for timesteps 190,192,194,196,198,200 on
timestep 200, etc. If Nrepeat=1 and Nfreq = 100, then no time
averaging is done; values are simply generated on timesteps
100,200,etc.</p>
<hrclass="docutils"/>
<p>The <em>origin_x</em>, <em>origin_y</em>, and <em>origin_z</em> parameters may be specified
by either a compute or a variable. This allows, for example, the
center of the spherical bins to be attached to the center of mass of a
group of atoms. If a variable origin is used and periodic boundary
conditions are in effect, then the origin will be wrapped across
periodic boundaries whenever it changes so that it is always inside
the simulation box.</p>
<hrclass="docutils"/>
<p>The atom attribute values (vx,vy,vz,fx,fy,fz) are self-explanatory.
Note that other atom attributes (including atom postitions x,y,z) can
be used as inputs to this fix by using the <aclass="reference internal"href="compute_property_atom.html"><spanclass="doc">compute property/atom</span></a> command and then specifying
an input value from that compute.</p>
<p>The <em>density/number</em> value means the number density is computed in
each bin, i.e. a weighting of 1 for each atom. The <em>density/mass</em>
value means the mass density is computed in each bin, i.e. each atom
is weighted by its mass. The resulting density is normalized by the
volume of the bin so that units of number/volume or density are
<h2>Restart, fix_modify, output, run start/stop, minimize info</h2>
<p>No information about this fix is written to <aclass="reference internal"href="restart.html"><spanclass="doc">binary restart files</span></a>. None of the <aclass="reference internal"href="fix_modify.html"><spanclass="doc">fix_modify</span></a> options
are relevant to this fix.</p>
<p>This fix computes a global array of values which can be accessed by
various <aclass="reference internal"href="Section_howto.html#howto-15"><spanclass="std std-ref">output commands</span></a>. The values can
only be accessed on timesteps that are multiples of <em>Nfreq</em> since that
is when averaging is performed. The global array has # of rows =
Nbins and # of columns = 2+Nvalues. The first column contains the
radius at the center of the shell. For units <em>reduced</em>, this is in
reduced units, while for units <em>box</em> and <em>lattice</em> this is in box
units. The next column has the count of atoms in that bin, and the
remaining columns are the Nvalue quantities. When the array is
accessed with an I that exceeds the current number of bins, than a 0.0
is returned by the fix instead of an error. The array values
calculated by this fix are “intensive”, since they are already
normalized by the count of atoms in each bin.</p>
<p>No parameter of this fix can be used with the <em>start/stop</em> keywords of
the <aclass="reference internal"href="run.html"><spanclass="doc">run</span></a> command. This fix is not invoked during <aclass="reference internal"href="minimize.html"><spanclass="doc">energy minimization</span></a>.</p>
</div>
<divclass="section"id="restrictions">
<h2>Restrictions</h2>
<p>When the <em>ave</em> keyword is set to <em>running</em> or <em>window</em> then the number
of bins must remain the same during the simulation, so that the
appropriate averaging can be done. This will be the case if the
simulation box size doesn’t change or if the <em>units</em> keyword is set to
<em>reduced</em>.</p>
<p>This style is part of the USER-MISC package. It is only enabled if
LAMMPS is build with that package. See the <spanclass="xref std std-ref">Making of LAMMPS</span> section for more info.</p>
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