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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 print command
</H3>
<P><B>Syntax:</B>
</P>
<PRE>fix ID group-ID print N string
</PRE>
<UL><LI>ID, group-ID are documented in <A HREF = "fix.html">fix</A> command
<LI>print = style name of this fix command
<LI>N = print every N steps
<LI>string = text string to print with optional variable names
</UL>
<P><B>Examples:</B>
</P>
<PRE>fix extra all print 100 "Coords of marker atom = $x $y $z"
</PRE>
<P><B>Description:</B>
</P>
<P>Print a text string to the screen and logfile every N steps during a
simulation run. This can be used for diagnostic purposes or even as a
debugging tool to monitor some quantity during a run. The text string
must be a single argument, so it should be enclosed in double quotes
if it is more than one word. If it contains variables it must be
enclosed in double quotes to insure they are not evaluated when the
input script is read, but will instead be evaluated when the string is
printed.
</P>
<P>See the <A HREF = "variable.html">variable</A> command for a description of <I>equal</I>
style variables which are the most useful ones to use with the fix
print command, since they are evaluated afresh each timestep that the
fix print line is output. Equal-style variables can calculate complex
formulas involving atom and group properties, mathematical operations,
other variables, etc.
</P>
<P><B>Restrictions:</B>
</P>
<P>If <I>equal</I>-style variables are used which contain
<A HREF = "thermo_style.html">thermo_style custom</A> keywords for energy such as
pe, eng, evdwl, ebond, etc, then they will only be up-to-date on
timesteps where thermodynamics are computed. For example, if you
output thermodynamics every 100 steps, but issue a fix print command
with N = 2 that contains such a variable, the printed value will only
be current on timesteps that are a multiple of 100. This is because
the potential functions in LAMMPS (pairwise, bond, etc) only compute
energies on timesteps when thermodynamic output is being performed.
</P>
<P><B>Related commands:</B>
</P>
<P><A HREF = "variable.html">variable</A>, <A HREF = "print.html">print</A>
</P>
<P><B>Default:</B> none
</P>
</HTML>
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