forked from lijiext/lammps
142 lines
5.0 KiB
Plaintext
142 lines
5.0 KiB
Plaintext
.. index:: write_restart
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write_restart command
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=====================
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Syntax
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""""""
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.. parsed-literal::
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write_restart file keyword value ...
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* file = name of file to write restart information to
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* zero or more keyword/value pairs may be appended
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* keyword = *fileper* or *nfile*
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.. parsed-literal::
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*fileper* arg = Np
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Np = write one file for every this many processors
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*nfile* arg = Nf
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Nf = write this many files, one from each of Nf processors
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Examples
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""""""""
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.. parsed-literal::
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write_restart restart.equil
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write_restart restart.equil.mpiio
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write_restart poly.%.* nfile 10
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Description
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"""""""""""
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Write a binary restart file of the current state of the simulation.
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During a long simulation, the :doc:`restart <restart>` command is
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typically used to output restart files periodically. The
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write_restart command is useful after a minimization or whenever you
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wish to write out a single current restart file.
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Similar to :doc:`dump <dump>` files, the restart filename can contain
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two wild-card characters. If a "*" appears in the filename, it is
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replaced with the current timestep value. If a "%" character appears
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in the filename, then one file is written by each processor and the
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"%" character is replaced with the processor ID from 0 to P-1. An
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additional file with the "%" replaced by "base" is also written, which
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contains global information. For example, the files written for
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filename restart.% would be restart.base, restart.0, restart.1, ...
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restart.P-1. This creates smaller files and can be a fast mode of
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output and subsequent input on parallel machines that support parallel
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I/O. The optional *fileper* and *nfile* keywords discussed below can
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alter the number of files written.
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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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.. parsed-literal::
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make yes-mpiio # installs the MPIIO package
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make g++ # build LAMMPS for your platform
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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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Restart files can be read by a :doc:`read_restart <read_restart>`
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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 :ref:`-r command-line switch <start_7>` to convert a restart file to a data
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file.
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.. note::
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Although the purpose of restart files is to enable restarting a
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simulation from where it left off, not all information about a
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simulation is stored in the file. For example, the list of fixes that
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were specified during the initial run is not stored, which means the
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new input script must specify any fixes you want to use. Even when
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restart information is stored in the file, as it is for some fixes,
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commands may need to be re-specified in the new input script, in order
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to re-use that information. Details are usually given in the
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documentation of the respective command. Also, see the
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:doc:`read_restart <read_restart>` command for general information about
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what is stored in a restart file.
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----------
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The optional *nfile* or *fileper* keywords can be used in conjunction
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with the "%" wildcard character in the specified restart file name.
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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 *nfile* or
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*fileper* 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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The *nfile* 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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For the *fileper* 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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----------
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Restrictions
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""""""""""""
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This command requires inter-processor communication to migrate atoms
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before the restart file is written. This means that your system must
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be ready to perform a simulation before using this command (force
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fields setup, atom masses initialized, etc).
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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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Related commands
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""""""""""""""""
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:doc:`restart <restart>`, :doc:`read_restart <read_restart>`,
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:doc:`write_data <write_data>`
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**Default:** none
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.. _lws: http://lammps.sandia.gov
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.. _ld: Manual.html
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.. _lc: Section_commands.html#comm
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