2006-09-22 00:22:34 +08:00
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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>
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<HR>
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<H3>read_restart command
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</H3>
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<P><B>Syntax:</B>
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</P>
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<PRE>read_restart file
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</PRE>
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<UL><LI>file = name of binary restart file to read in
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</UL>
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<P><B>Examples:</B>
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</P>
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<PRE>read_restart save.10000
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read_restart restart.*
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read_restart poly.*.%
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</PRE>
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<PRE>
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</PRE>
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<P><B>Description:</B>
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</P>
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2007-06-25 22:36:36 +08:00
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<P>Read in a previously saved simulation from a restart file. This
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allows continuation of a previous run. Information about what is
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stored in a restart file is given below.
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2006-09-22 00:22:34 +08:00
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</P>
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<P>Restart files are saved in binary format to enable exact restarts,
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meaning that the trajectories of a restarted run will precisely match
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those produced by the original run had it continued on. Several
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things can prevent exact restarts due to round-off effects, in which
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case the trajectories in the 2 runs will slowly diverge. These
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include running on a different number of processors or changing
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certain settings such as those set by the <A HREF = "newton.html">newton</A> or
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2010-10-28 04:54:22 +08:00
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<A HREF = "processors.html">processors</A> commands. LAMMPS will issue a warning in
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2006-09-22 00:22:34 +08:00
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these cases. Certain fixes will also not restart exactly, though they
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2007-06-25 22:36:36 +08:00
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should provide statistically similar results. These include <A HREF = "fix_shake.html">fix
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shake</A> and <A HREF = "fix_langevin.html">fix langevin</A>. If a
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restarted run is immediately different than the run which produced the
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2010-11-02 23:05:51 +08:00
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restart file, it could be a LAMMPS bug, so consider <A HREF = "Section_errors.html#10_2">reporting
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2007-06-25 22:36:36 +08:00
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it</A> if you think the behavior is wrong.
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2006-09-22 00:22:34 +08:00
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</P>
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<P>Because restart files are binary, they may not be portable to other
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machines. They can be converted to ASCII data files using the
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2007-03-08 09:01:08 +08:00
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<A HREF = "Section_tools.html#restart">restart2data tool</A> in the tools
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sub-directory of the LAMMPS distribution.
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2006-09-22 00:22:34 +08:00
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</P>
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<P>Similar to how restart files are written (see the
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<A HREF = "write_restart.html">write_restart</A> and <A HREF = "restart.html">restart</A>
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commands), the restart filename can contain two wild-card characters.
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If a "*" appears in the filename, the directory is searched for all
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filenames that match the pattern where "*" is replaced with a timestep
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value. The file with the largest timestep value is read in. Thus,
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this effectively means, read the latest restart file. It's useful if
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you want your script to continue a run from where it left off. See
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the <A HREF = "run.html">run</A> command and its "upto" option for how to specify
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the run command so it doesn't need to be changed either.
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</P>
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<P>If a "%" character appears in the restart filename, LAMMPS expects a
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set of multiple files to exist. The <A HREF = "restart.html">restart</A> and
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<A HREF = "write_restart.html">write_restart</A> commands explain how such sets are
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created. Read_restart will first read a filename where "%" is
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replaced by "base". This file tells LAMMPS how many processors
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created the set. Read_restart then reads the additional files. For
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example, if the restart file was specified as save.% when it was
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written, then read_restart reads the files save.base, save.0, save.1,
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... save.P-1, where P is the number of processors that created the
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2010-09-11 07:00:40 +08:00
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restart file. The processors in the current LAMMPS simulation share
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the work of reading these files; each reads a roughly equal subset of
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the files. The number of processors which created the set can be
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different the number of processors in the current LAMMPS simulation.
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This can be a fast mode of input on parallel machines that support
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parallel I/O.
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2006-09-22 00:22:34 +08:00
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</P>
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<HR>
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2007-06-25 22:36:36 +08:00
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<P>A restart file stores the following information about a simulation:
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units and atom style, simulation box size and shape and boundary
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settings, group definitions, atom type settings such as mass and
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particle shape, individual atoms and their group assignments and
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molecular topology attributes, force field styles and coefficients,
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and <A HREF = "special_bonds.html">special_bonds</A> settings. This means that
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commands for these quantities do not need to be re-specified in the
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input script that reads the restart file, though you can redefine
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settings after the restart file is read.
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</P>
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<P>One exception is that some pair styles do not store their info in
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restart files. The doc pages for individual pair styles note if this
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is the case. This is also true of bond_style hybrid (and angle_style,
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dihedral_style, improper_style hybrid).
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</P>
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<P>Information about <A HREF = "kspace_style.html">kspace_style</A> settings are not
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stored in the restart file. Hence if you wish to use an Ewald or PPPM
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solver, these commands must be re-issued after the restart file is
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read.
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</P>
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<P>The list of <A HREF = "fix.html">fixes</A> used for a simulation is not stored in
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the restart file. This means the new input script should specify all
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fixes it will use. Note that some fixes store an internal "state"
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which is written to the restart file. This allows the fix to continue
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on with its calculations in a restarted simulation. To re-enable such
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a fix, the fix command in the new input script must use the same
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fix-ID and group-ID as was used in the input script that wrote the
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restart file. If a match is found, LAMMPS prints a message indicating
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that the fix is being re-enabled. If no match is found before the
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first run or minimization is performed by the new script, the "state"
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information for the saved fix is discarded. See the doc pages for
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individual fixes for info on which ones can be restarted in this
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manner.
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2006-09-22 00:22:34 +08:00
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</P>
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<P>Bond interactions (angle, etc) that have been turned off by the <A HREF = "fix_shake.html">fix
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shake</A> or <A HREF = "delete_bonds.html">delete_bonds</A> command will
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be written to a restart file as if they are turned on. This means
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they will need to be turned off again in a new run after the restart
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file is read.
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</P>
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<P>Bonds that are broken (e.g. by a bond-breaking potential) are written
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to the restart file as broken bonds with a type of 0. Thus these
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bonds will still be broken when the restart file is read.
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</P>
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2007-06-25 22:36:36 +08:00
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<P>IMPORTANT NOTE: No other information is stored in the restart file.
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This means that an input script that reads a restart file should
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specify settings for quantities like <A HREF = "timestep.html">timestep size</A>,
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<A HREF = "thermo_style.html">thermodynamic</A> and <A HREF = "dump.html">dump</A> output,
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<A HREF = "region.html">geometric regions</A>, etc.
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2006-09-22 00:22:34 +08:00
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</P>
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2007-06-25 22:36:36 +08:00
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<P><B>Restrictions:</B> none
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</P>
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<P><B>Related commands:</B>
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</P>
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<P><A HREF = "read_data.html">read_data</A>, <A HREF = "write_restart.html">write_restart</A>,
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<A HREF = "restart.html">restart</A>
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</P>
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<P><B>Default:</B> none
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</P>
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</HTML>
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