git-svn-id: svn://svn.icms.temple.edu/lammps-ro/trunk@14950 f3b2605a-c512-4ea7-a41b-209d697bcdaa

doc/html/_sources/write_restart.txt

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+.. index:: write_restart
+
+write_restart command
+=====================
+
+Syntax
+""""""
+
+.. parsed-literal::
+
+   write_restart file keyword value ...
+
+* file = name of file to write restart information to
+* zero or more keyword/value pairs may be appended
+* keyword = *fileper* or *nfile*
+.. parsed-literal::
+
+     *fileper* arg = Np
+       Np = write one file for every this many processors
+     *nfile* arg = Nf
+       Nf = write this many files, one from each of Nf processors
+
+
+
+Examples
+""""""""
+
+.. parsed-literal::
+
+   write_restart restart.equil
+   write_restart restart.equil.mpiio
+   write_restart poly.%.* nfile 10
+
+Description
+"""""""""""
+
+Write a binary restart file of the current state of the simulation.
+
+During a long simulation, the :doc:`restart <restart>` command is
+typically used to output restart files periodically.  The
+write_restart command is useful after a minimization or whenever you
+wish to write out a single current restart file.
+
+Similar to :doc:`dump <dump>` files, the restart filename can contain
+two wild-card characters.  If a "*" appears in the filename, it is
+replaced with the current timestep value.  If a "%" character appears
+in the filename, then one file is written by each processor and the
+"%" character is replaced with the processor ID from 0 to P-1.  An
+additional file with the "%" replaced by "base" is also written, which
+contains global information.  For example, the files written for
+filename restart.% would be restart.base, restart.0, restart.1, ...
+restart.P-1.  This creates smaller files and can be a fast mode of
+output and subsequent input on parallel machines that support parallel
+I/O.  The optional *fileper* and *nfile* keywords discussed below can
+alter the number of files written.
+
+The restart file can also be written in parallel as one large binary
+file via the MPI-IO library, which is part of the MPI standard for
+versions 2.0 and above.  Using MPI-IO requires two steps.  First,
+build LAMMPS with its MPIIO package installed, e.g.
+
+.. parsed-literal::
+
+   make yes-mpiio    # installs the MPIIO package
+   make g++          # build LAMMPS for your platform
+
+Second, use a restart filename which contains ".mpiio".  Note that it
+does not have to end in ".mpiio", just contain those characters.
+Unlike MPI-IO dump files, a particular restart file must be both
+written and read using MPI-IO.
+
+Restart files can be read by a :doc:`read_restart <read_restart>`
+command to restart a simulation from a particular state.  Because the
+file is binary (to enable exact restarts), it may not be readable on
+another machine.  In this case, you can use the :ref:`-r command-line switch <start_7>` to convert a restart file to a data
+file.
+
+.. note::
+
+   Although the purpose of restart files is to enable restarting a
+   simulation from where it left off, not all information about a
+   simulation is stored in the file.  For example, the list of fixes that
+   were specified during the initial run is not stored, which means the
+   new input script must specify any fixes you want to use.  Even when
+   restart information is stored in the file, as it is for some fixes,
+   commands may need to be re-specified in the new input script, in order
+   to re-use that information. Details are usually given in the
+   documentation of the respective command. Also, see the
+   :doc:`read_restart <read_restart>` command for general information about
+   what is stored in a restart file.
+
+
+----------
+
+
+The optional *nfile* or *fileper* keywords can be used in conjunction
+with the "%" wildcard character in the specified restart file name.
+As explained above, the "%" character causes the restart file to be
+written in pieces, one piece for each of P processors.  By default P =
+the number of processors the simulation is running on.  The *nfile* or
+*fileper* keyword can be used to set P to a smaller value, which can
+be more efficient when running on a large number of processors.
+
+The *nfile* keyword sets P to the specified Nf value.  For example, if
+Nf = 4, and the simulation is running on 100 processors, 4 files will
+be written, by processors 0,25,50,75.  Each will collect information
+from itself and the next 24 processors and write it to a restart file.
+
+For the *fileper* keyword, the specified value of Np means write one
+file for every Np processors.  For example, if Np = 4, every 4th
+processor (0,4,8,12,etc) will collect information from itself and the
+next 3 processors and write it to a restart file.
+
+
+----------
+
+
+Restrictions
+""""""""""""
+
+
+This command requires inter-processor communication to migrate atoms
+before the restart file is written.  This means that your system must
+be ready to perform a simulation before using this command (force
+fields setup, atom masses initialized, etc).
+
+To write and read restart files in parallel with MPI-IO, the MPIIO
+package must be installed.
+
+Related commands
+""""""""""""""""
+
+:doc:`restart <restart>`, :doc:`read_restart <read_restart>`,
+:doc:`write_data <write_data>`
+
+**Default:** none
+
+
+.. _lws: http://lammps.sandia.gov
+.. _ld: Manual.html
+.. _lc: Section_commands.html#comm