This folder contains several LAMMPS input scripts and a python module file py_integrate.py to demonstrate the use of the fix style python/integrate. in.fix_python_integrate_melt: This is a version of the melt example which replaces the default NVE integrator with a Python implementation. Fix python/integrate is used to create an instance of the py_integrate.NVE class which implements the required interface. It demonstrates how to access LAMMPS data as numpy arrays. This gives direct access to memory owned by the C++ code, allows easy manipulation through numpy operations and avoids unnecessary copies. in.fix_python_integrate_melt_opt: This version of melt example uses NVE_Opt instead of NVE. While this Python implementation is still much slower than the native version, it shows that simple code transformations can lead to speedups.