The Makefile.lammps file in this directory is used when building LAMMPS with its PYTHON package installed. The file has several settings needed to compile and link LAMMPS with the Python library. You should choose a Makefile.lammps.* file compatible with your system and your version of Python, and copy it to Makefile.lammps before building LAMMPS itself. You may need to edit one of the provided files to match your system.

Note that is not currently possible to use the PYTHON package with Python 3, only with Python 2. The C API changed from Python 2 to 3 and the LAMMPS code is not compatible with both.

If you create a new Makefile.lammps file suitable for some version of Python on some system, that is not a match to one of the provided Makefile.lammps.* files, you can send it to the developers, and we can include it in the distribution for others to use.

To illustrate, these are example settings from the Makefile.lammps.python2.7 file:

python_SYSINC = -I/usr/local/include/python2.7 python_SYSLIB = -lpython2.7 -lnsl -ldl -lreadline -ltermcap -lpthread -lutil -lm python_SYSPATH =

python_SYSINC refers to the directory where Python's Python.h file is found. LAMMPS includes this file.

python_SYSLIB refers to the libraries needed to link to from an application (LAMMPS in this case) to "embed" Python in the application. The Python library itself is listed (-lpython2.7) are are several system libraries needed by Python.

python_SYSPATH = refers to the path (e.g. -L/usr/local/lib) where the Python library can be found. You may not need this setting if the path is already included in your LD_LIBRARY_PATH environment variable.

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Note that the trickiest issue to figure out for inclusion in Makefile.lammps is what system libraries are needed by your Python to run in embedded mode on your machine.

Here is what this Python doc page says about it:

https://docs.python.org/2/extending/embedding.html#compiling-and-linking-under-unix-like-systems

"It is not necessarily trivial to find the right flags to pass to your compiler (and linker) in order to embed the Python interpreter into your application, particularly because Python needs to load library modules implemented as C dynamic extensions (.so files) linked against it.

To find out the required compiler and linker flags, you can execute the pythonX.Y-config script which is generated as part of the installation process (a python-config script may also be available)."

It then gives examples of how to use the pythonX.Y-config script and further instructions for what to do if that doesn't work.