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add info about restart files

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This commit is contained in:
Axel Kohlmeyer
2025-03-27 16:29:13 -04:00
parent 2542b989ee
commit 738fb4a502
1 changed files with 36 additions and 3 deletions
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39
doc/src/Run_formats.rst
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@ -374,13 +374,46 @@ There are also optional sections, e.g. about :doc:`SHAKE <fix_shake>` and
command is issues *before* the simulation box is defined. Otherwise, the
molecule command can derive the required settings internally.
Potential file
^^^^^^^^^^^^^^
Native Dump file
^^^^^^^^^^^^^^^^
Restart file
^^^^^^^^^^^^
LAMMPS restart files are binary files and not available in text format.
They can be identified by the first few bytes that contain the (C-style)
string "LammpS RestartT" as `magic string
<https://en.wikipedia.org/wiki/Magic_string>`_. This is followed by a
16-bit integer of the number 1 used for detecting whether the computer
writing the restart has the same `endianness
<https://en.wikipedia.org/wiki/Endianness>`_ as the computer reading it.
If not the file cannot be read correctly. This is followed by a 32-bit
integer indicating the file format revision (currently 3), which can be
used to implement backward compatibility for reading older revisions.
This information has been added to the `Unix "file" command's
<https://www.darwinsys.com/file/>` "magic" file so that restart files
can be identified without opening them. If you have a fairly recent
version, it should already be included. If you have an older version,
the LAMMPS source package :ref:`contains a file with the necessary
additions <magic>`.
The rest of the file is organized in sections of a 32-bit signed integer
constant indicating the kind of content and the corresponding value (or
values). If those values are arrays (including C-style strings), then
the integer constant is followed by a 32-bit integer indicating the
length of the array. This mechanism will read the data regardless of
the ordering of the sections. Symbolic names of the section constants
are in the ``lmprestart.h`` header file.
LAMMPS restart files are not expected to be portable between platforms
or LAMMPS versions, but changes to the file format are rare.
Dump file
^^^^^^^^^
Potential files
^^^^^^^^^^^^^^^