System properties
=================

Similar to what is described in :doc:`Library_properties`, the instances of
:py:class:`lammps <lammps.lammps>` can be used to extract different kinds
of information about the active LAMMPS instance and also to modify some of it.

In some cases the data returned is a direct reference to the original data
inside LAMMPS cast to ``ctypes`` pointers. Where possible, the wrappers will
determine the ``ctypes`` data type and cast pointers accordingly. If
``numpy`` is installed arrays can also be extracted as numpy arrays, which
will access the C arrays directly and have the correct dimensions to protect
against invalid accesses.

.. warning::

   When accessing per-atom data,
   please note that this data is the per-processor local data and indexed
   accordingly. These arrays can change sizes and order at every neighbor list
   rebuild and atom sort event as atoms are migrating between subdomains.

.. code-block:: python

   from lammps import lammps

   lmp = lammps()
   lmp.file("in.sysinit")

   natoms = lmp.get_natoms()
   print(f"running simulation with {natoms} atoms")

   lmp.command("run 1000 post no");

   for i in range(10):
      lmp.command("run 100 pre no post no")
      pe = lmp.get_thermo("pe")
      ke = lmp.get_thermo("ke")
      print(f"PE = {pe}\nKE = {ke}")

   lmp.close()

**Methods**:

* :py:meth:`version() <lammps.lammps.version()>`: return the numerical version id, e.g. LAMMPS 2 Sep 2015 -> 20150902
* :py:meth:`get_thermo() <lammps.lammps.get_thermo()>`: return current value of a thermo keyword
* :py:meth:`last_thermo() <lammps.lammps.last_thermo()>`: return a dictionary of the last thermodynamic output
* :py:meth:`get_natoms() <lammps.lammps.get_natoms()>`: total # of atoms as int
* :py:meth:`reset_box() <lammps.lammps.reset_box()>`: reset the simulation box size
* :py:meth:`extract_setting() <lammps.lammps.extract_setting()>`: return a global setting
* :py:meth:`extract_global() <lammps.lammps.extract_global()>`: extract a global quantity
* :py:meth:`extract_box() <lammps.lammps.extract_box()>`: extract box info
* :py:meth:`create_atoms() <lammps.lammps.create_atoms()>`: create N atoms with IDs, types, x, v, and image flags

**Properties**:

* :py:attr:`last_thermo_step <lammps.lammps.last_thermo_step>`: the last timestep thermodynamic output was computed