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read_restart.html
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<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>read_restart command
</H3>
<P><B>Syntax:</B>
</P>
<PRE>read_restart file
</PRE>
<UL><LI>file = name of binary restart file to read in
</UL>
<P><B>Examples:</B>
</P>
<PRE>read_restart save.10000
read_restart restart.*
read_restart poly.*.%
</PRE>
<PRE>
</PRE>
<P><B>Description:</B>
</P>
<P>Read in a previously saved problem from a restart file. This allows
continuation of a previous run.
</P>
<P>Restart files are saved in binary format to enable exact restarts,
meaning that the trajectories of a restarted run will precisely match
those produced by the original run had it continued on. Several
things can prevent exact restarts due to round-off effects, in which
case the trajectories in the 2 runs will slowly diverge. These
include running on a different number of processors or changing
certain settings such as those set by the <A HREF = "newton.html">newton</A> or
<A HREF = "processors.html">processors</A> commands. LAMMPS will issue a WARNING in
these cases. Certain fixes will also not restart exactly, though they
should provide statistically similar results. These include the shake
and langevin styles. If a restarted run is immediately different than
the run which produced the restart file, it could be a LAMMPS bug, so
consider <A HREF = "Section_errors.html#9_2">reporting it</A> if you think the
behavior is wrong.
</P>
<P>Because restart files are binary, they may not be portable to other
machines. They can be converted to ASCII data files using the
<A HREF = "Section_tools.html#restart">restart2data tool</A> in the tools
sub-directory of the LAMMPS distribution.
</P>
<P>Similar to how restart files are written (see the
<A HREF = "write_restart.html">write_restart</A> and <A HREF = "restart.html">restart</A>
commands), the restart filename can contain two wild-card characters.
If a "*" appears in the filename, the directory is searched for all
filenames that match the pattern where "*" is replaced with a timestep
value. The file with the largest timestep value is read in. Thus,
this effectively means, read the latest restart file. It's useful if
you want your script to continue a run from where it left off. See
the <A HREF = "run.html">run</A> command and its "upto" option for how to specify
the run command so it doesn't need to be changed either.
</P>
<P>If a "%" character appears in the restart filename, LAMMPS expects a
set of multiple files to exist. The <A HREF = "restart.html">restart</A> and
<A HREF = "write_restart.html">write_restart</A> commands explain how such sets are
created. Read_restart will first read a filename where "%" is
replaced by "base". This file tells LAMMPS how many processors
created the set. Read_restart then reads the additional files. For
example, if the restart file was specified as save.% when it was
written, then read_restart reads the files save.base, save.0, save.1,
... save.P-1, where P is the number of processors that created the
restart file. Note that only a single processor reads all the files,
so the input does not use parallel I/O. The number of processors
which created the set can be different the number of processors in the
current LAMMPS simulation.
</P>
<HR>
<P>A restart file stores the units and atom style, simulation box
attibutes (including whether it is an orthogonal box or a
non-orthogonal parallelepiped with triclinic symmetry), individual
atoms and their attributes including molecular topology, force field
styles and coefficients, <A HREF = "special_bonds.html">special_bonds</A> settings,
and atom group definitions. This means that commands for these
quantities do not need to be specified in your input script that reads
the restart file. The exceptions to this are listed below in the
Restrictions section.
</P>
<P>Information about the <A HREF = "kspace_style.html">kspace_style</A> settings are
not stored in the restart file. Hence if you wish to invoke an Ewald
or PPPM solver, this command must be re-issued after the restart file
is read.
</P>
<P>The restart file also stores values for any fixes that require state
information to enable restarting where they left off. These include
the <I>nvt</I> and <I>npt</I> styles that have a global state, as well as the
<I>msd</I> and <I>wall/gran</I> styles that store information about each atom.
</P>
<P><A HREF = "fix.html">Fix</A> commands are not stored in the restart file which means
they must be specified in the input script that reads the restart
file. To re-enable a fix whose state was stored in the restart file,
the fix command in the new input script must use the same fix-ID and
group-ID as the input script that wrote the restart file. LAMMPS will
print a message indicating that the fix is being re-enabled.
</P>
<P>Note that no other information is stored in the restart file. This
means that your new input script should specify settings for
quantities like timestep size, thermodynamic and dump output, etc.
</P>
<P>Bond interactions (angle, etc) that have been turned off by the <A HREF = "fix_shake.html">fix
shake</A> or <A HREF = "delete_bonds.html">delete_bonds</A> command will
be written to a restart file as if they are turned on. This means
they will need to be turned off again in a new run after the restart
file is read.
</P>
<P>Bonds that are broken (e.g. by a bond-breaking potential) are written
to the restart file as broken bonds with a type of 0. Thus these
bonds will still be broken when the restart file is read.
</P>
<P><B>Restrictions:</B>
</P>
<P>The <A HREF = "pair_style.html">pair_style</A> <I>eam</I>, <I>table</I>, and <I>hybrid</I> styles
do not store coefficient data for individual atom type pairs in the
restart file. Nor does the <A HREF = "bond_style.html">bond_style hybrid</A> style
(angle, dihedral hybrid, etc). Thus for these styles you must use new
<A HREF = "pair_coeff.html">pair_coeff</A> and <A HREF = "bond_coeff.html">bond_coeff</A> (angle,
dihedral, etc) commands to read the appropriate tabulated files or
reset the coefficients after the restart file is read.
</P>
<P><B>Related commands:</B>
</P>
<P><A HREF = "read_data.html">read_data</A>, <A HREF = "write_restart.html">write_restart</A>,
<A HREF = "restart.html">restart</A>
</P>
<P><B>Default:</B> none
</P>
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