<p>Define a fix that stores attributes for each atom in the group at the
time the fix is defined. If <em>N</em> is 0, then the values are never
updated, so this is a way of archiving an atom attribute at a given
time for future use in a calculation or output. See the discussion of
<aclass="reference internal"href="Section_howto.html#howto-15"><spanclass="std std-ref">output commands</span></a> that take fixes as
inputs.</p>
<p>If <em>N</em> is not zero, then the attributes will be updated every <em>N</em>
steps.</p>
<divclass="admonition note">
<pclass="first admonition-title">Note</p>
<pclass="last">Actually, only atom attributes specified by keywords like <em>xu</em>
or <em>vy</em> or <em>radius</em> are initially stored immediately at the point in
your input script when the fix is defined. Attributes specified by a
compute, fix, or variable are not initially stored until the first run
following the fix definition begins. This is because calculating
those attributes may require quantities that are not defined in
between runs.</p>
</div>
<p>The list of possible attributes is the same as that used by the <aclass="reference internal"href="dump.html"><spanclass="doc">dump custom</span></a> command, which describes their meaning.</p>
<p>If the <em>com</em> keyword is set to <em>yes</em> then the <em>xu</em>, <em>yu</em>, and <em>zu</em>
inputs store the position of each atom relative to the center-of-mass
of the group of atoms, instead of storing the absolute position.</p>
<p>The requested values are stored in a per-atom vector or array as
discussed below. Zeroes are stored for atoms not in the specified
group.</p>
<p><strong>Restart, fix_modify, output, run start/stop, minimize info:</strong></p>
<p>This fix writes the per-atom values it stores to <aclass="reference internal"href="restart.html"><spanclass="doc">binary restart files</span></a>, so that the values can be restored when a
simulation is restarted. See the <aclass="reference internal"href="read_restart.html"><spanclass="doc">read_restart</span></a>
command for info on how to re-specify a fix in an input script that
reads a restart file, so that the operation of the fix continues in an
uninterrupted fashion.</p>
<p>None of the <aclass="reference internal"href="fix_modify.html"><spanclass="doc">fix_modify</span></a> options are relevant to this
fix.</p>
<p>If a single input is specified, this fix produces a per-atom vector.
If multiple inputs are specified, a per-atom array is produced where
the number of columns for each atom is the number of inputs. These
can be accessed by various <aclass="reference internal"href="Section_howto.html#howto-15"><spanclass="std std-ref">output commands</span></a>. The per-atom values be
accessed on any timestep.</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>
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