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>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>restart 0
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restart N root keyword value ...
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restart N file1 file2 keyword value ...
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</PRE>
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<UL><LI>N = write a restart file every this many timesteps
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<LI>N can be a variable (see below)
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<LI>root = filename to which timestep # is appended
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2006-09-22 00:22:34 +08:00
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<LI>file1,file2 = two full filenames, toggle between them when writing file
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<LI>zero or more keyword/value pairs may be appended
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<LI>keyword = <I>fileper</I> or <I>nfile</I>
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<PRE> <I>fileper</I> arg = Np
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Np = write one file for every this many processors
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<I>nfile</I> arg = Nf
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Nf = write this many files, one from each of Nf processors
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</PRE>
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2006-09-22 00:22:34 +08:00
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</UL>
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<P><B>Examples:</B>
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</P>
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<PRE>restart 0
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restart 1000 poly.restart
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2014-01-22 23:31:45 +08:00
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restart 1000 poly.restart.mpiio
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restart 1000 restart.*.equil
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2013-12-07 06:36:18 +08:00
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restart 10000 poly.%.1 poly.%.2 nfile 10
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restart v_mystep poly.restart
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</PRE>
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<P><B>Description:</B>
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</P>
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<P>Write out a binary restart file every so many timesteps, in either or
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both of two modes, as a run proceeds. A value of 0 means do not write
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out any restart files. The two modes are as follows. If one filename
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is specified, a series of filenames will be created which include the
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timestep in the filename. If two filenames are specified, only 2
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restart files will be created, with those names. LAMMPS will toggle
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between the 2 names as it writes successive restart files.
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</P>
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<P>Note that you can specify the restart command twice, once with a
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single filename and once with two filenames. This would allow you,
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for example, to write out archival restart files every 100000 steps
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using a single filenname, and more frequent temporary restart files
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every 1000 steps, using two filenames. Using restart 0 will turn off
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both modes of output.
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2006-09-22 00:22:34 +08:00
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</P>
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<P>Similar to <A HREF = "dump.html">dump</A> files, the restart filename(s) can contain
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two wild-card characters.
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</P>
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<P>If a "*" appears in the single filename, it is replaced with the
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current timestep value. This is only recognized when a single
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filename is used (not when toggling back and forth). Thus, the 3rd
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example above creates restart files as follows: restart.1000.equil,
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restart.2000.equil, etc. If a single filename is used with no "*",
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then the timestep value is appended. E.g. the 2nd example above
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creates restart files as follows: poly.restart.1000,
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poly.restart.2000, etc.
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</P>
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<P>If a "%" character appears in the restart filename(s), then one file
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is written for each processor and the "%" character is replaced with
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the processor ID from 0 to P-1. An additional file with the "%"
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replaced by "base" is also written, which contains global information.
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For example, the files written on step 1000 for filename restart.%
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would be restart.base.1000, restart.0.1000, restart.1.1000, ...,
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restart.P-1.1000. This creates smaller files and can be a fast mode
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of output and subsequent input on parallel machines that support
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parallel I/O. The optional <I>fileper</I> and <I>nfile</I> keywords discussed
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below can alter the number of files written.
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</P>
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2014-01-22 23:31:45 +08:00
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<P>The restart file can also be written in parallel as one large binary
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file via the MPI-IO library, which is part of the MPI standard for
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versions 2.0 and above. Using MPI-IO requires two steps. First,
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build LAMMPS with its MPIIO package installed, e.g.
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</P>
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<PRE>make yes-mpiio # installs the MPIIO package
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make g++ # build LAMMPS for your platform
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</PRE>
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<P>Second, use a restart filename which contains ".mpiio". Note that it
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does not have to end in ".mpiio", just contain those characters.
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Unlike MPI-IO dump files, a particular restart file must be both
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written and read using MPI-IO.
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</P>
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<P>Restart files are written on timesteps that are a multiple of N but
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not on the first timestep of a run or minimization. You can use the
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<A HREF = "write_restart.html">write_restart</A> command to write a restart file
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before a run begins. A restart file is not written on the last
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timestep of a run unless it is a multiple of N. A restart file is
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written on the last timestep of a minimization if N > 0 and the
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minimization converges.
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</P>
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<P>Instead of a numeric value, N can be specifed as an <A HREF = "variable.html">equal-style
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variable</A>, which should be specified as v_name, where
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name is the variable name. In this case, the variable is evaluated at
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the beginning of a run to determine the next timestep at which a
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restart file will be written out. On that timestep, the variable will
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be evaluated again to determine the next timestep, etc. Thus the
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variable should return timestep values. See the stagger() and
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logfreq() and stride() math functions for <A HREF = "variable.html">equal-style
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variables</A>, as examples of useful functions to use in
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this context. Other similar math functions could easily be added as
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options for <A HREF = "variable.html">equal-style variables</A>.
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</P>
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<P>For example, the following commands will write restart files
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every step from 1100 to 1200, and could be useful for debugging
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a simulation where something goes wrong at step 1163:
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</P>
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<PRE>variable s equal stride(1100,1200,1)
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restart v_s tmp.restart
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</PRE>
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<HR>
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2006-09-22 00:22:34 +08:00
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<P>See the <A HREF = "read_restart.html">read_restart</A> command for information about
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what is stored in a restart file.
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</P>
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<P>Restart files can be read by a <A HREF = "read_restart.html">read_restart</A>
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command to restart a simulation from a particular state. Because the
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file is binary (to enable exact restarts), it may not be readable on
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another machine. In this case, you can use the <A HREF = "Section_start.html#start_7">-r command-line
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switch</A> to convert a restart file to a data
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file.
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</P>
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<P>IMPORTANT NOTE: Although the purpose of restart files is to enable
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restarting a simulation from where it left off, not all information
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about a simulation is stored in the file. For example, the list of
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fixes that were specified during the initial run is not stored, which
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means the new input script must specify any fixes you want to use.
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Even when restart information is stored in the file, as it is for some
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fixes, commands may need to be re-specified in the new input script,
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in order to re-use that information. See the
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<A HREF = "read_restart.html">read_restart</A> command for information about what is
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stored in a restart file.
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</P>
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2013-11-23 01:34:49 +08:00
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<HR>
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<P>The optional <I>nfile</I> or <I>fileper</I> keywords can be used in conjunction
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with the "%" wildcard character in the specified restart file name(s).
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As explained above, the "%" character causes the restart file to be
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written in pieces, one piece for each of P processors. By default P =
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the number of processors the simulation is running on. The <I>nfile</I> or
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<I>fileper</I> keyword can be used to set P to a smaller value, which can
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be more efficient when running on a large number of processors.
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</P>
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<P>The <I>nfile</I> keyword sets P to the specified Nf value. For example, if
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Nf = 4, and the simulation is running on 100 processors, 4 files will
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be written, by processors 0,25,50,75. Each will collect information
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from itself and the next 24 processors and write it to a restart file.
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</P>
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<P>For the <I>fileper</I> keyword, the specified value of Np means write one
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file for every Np processors. For example, if Np = 4, every 4th
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processor (0,4,8,12,etc) will collect information from itself and the
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next 3 processors and write it to a restart file.
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2006-09-22 00:22:34 +08:00
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</P>
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2013-11-23 01:34:49 +08:00
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<HR>
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2014-01-22 23:31:45 +08:00
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<P><B>Restrictions:</B>
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</P>
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<P>To write and read restart files in parallel with MPI-IO, the MPIIO
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package must be installed.
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2006-09-22 00:22:34 +08:00
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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 = "write_restart.html">write_restart</A>, <A HREF = "read_restart.html">read_restart</A>
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</P>
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<P><B>Default:</B>
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</P>
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<PRE>restart 0
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</PRE>
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</HTML>
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