68 lines
2.5 KiB
ReStructuredText
68 lines
2.5 KiB
ReStructuredText
.. _mpi4py_url: https://mpi4py.readthedocs.io/
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.. _python_create_lammps:
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Creating or deleting a LAMMPS object
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====================================
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With the Python interface the creation of a :cpp:class:`LAMMPS
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<LAMMPS_NS::LAMMPS>` instance is included in the constructor for the
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:py:class:`lammps <lammps.lammps>` class. Internally it will call either
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:cpp:func:`lammps_open` or :cpp:func:`lammps_open_no_mpi` from the C library
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API to create the class instance.
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All arguments are optional. The *name* argument allows loading a
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LAMMPS shared library that is named ``liblammps_machine.so`` instead of
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the default name of ``liblammps.so``. In most cases the latter will be
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installed or used. The *ptr* argument is for use of the
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:py:mod:`lammps` module from inside a LAMMPS instance, e.g. with the
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:doc:`python <python>` command, where a pointer to the already existing
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:cpp:class:`LAMMPS <LAMMPS_NS::LAMMPS>` class instance can be passed
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to the Python class and used instead of creating a new instance. The
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*comm* argument may be used in combination with the `mpi4py <mpi4py_url_>`_
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module to pass an MPI communicator to LAMMPS and thus it is possible
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to run the Python module like the library interface on a subset of the
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MPI ranks after splitting the communicator.
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Here is a simple example using the LAMMPS Python interface:
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.. code-block:: python
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from lammps import lammps
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# NOTE: argv[0] is set by the lammps class constructor
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args = ["-log", "none"]
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# create LAMMPS instance
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lmp = lammps(cmdargs=args)
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# get and print numerical version code
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print("LAMMPS Version: ", lmp.version())
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# explicitly close and delete LAMMPS instance (optional)
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lmp.close()
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Same as with the :ref:`C library API <lammps_c_api>`, this will use the
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``MPI_COMM_WORLD`` communicator for the MPI library that LAMMPS was
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compiled with.
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The :py:func:`lmp.close() <lammps.lammps.close()>` call is
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optional since the LAMMPS class instance will also be deleted
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automatically during the :py:class:`lammps <lammps.lammps>` class
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destructor. Instead of :py:func:`lmp.close() <lammps.lammps.close()>`
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it is also possible to call :py:func:`lmp.finalize() <lammps.lammps.finalize()>`;
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this will destruct the LAMMPS instance, but also finalized and release
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the MPI and/or Kokkos environment if enabled and active.
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Note that you can create multiple LAMMPS objects in your Python
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script, and coordinate and run multiple simulations, e.g.
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.. code-block:: python
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from lammps import lammps
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lmp1 = lammps()
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lmp2 = lammps()
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lmp1.file("in.file1")
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lmp2.file("in.file2")
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