3.3. Link LAMMPS as a library to another code
LAMMPS can be used as a library by another application, including Python scripts. The files src/library.cpp and library.h define the C-style API for using LAMMPS as a library. See the Howto library doc page for a description of the interface and how to extend it for your needs.
The Build basics doc page explains how to build LAMMPS as either a shared or static library. This results in one of these 2 files:
liblammps.so # shared library liblammps.a # static library
Link with LAMMPS as a static library:
The calling application can link to LAMMPS as a static library with a link command like this:
g++ caller.o -L/home/sjplimp/lammps/src -llammps -o caller
The -L argument is the path to where the liblammps.a file is. The -llammps argument is shorthand for the file liblammps.a.
Link with LAMMPS as a shared library:
If you wish to link to liblammps.so, the operating system finds shared libraries to load at run-time using the environment variable LD_LIBRARY_PATH. To enable this you can do one of two things:
(1) Copy the liblammps.so file to a location the system can find it, such as /usr/local/lib. I.e. a directory already listed in your LD_LIBRARY_PATH variable. You can type
printenv LD_LIBRARY_PATH
to see what directories are in that list.
(2) Add the LAMMPS src directory (or the directory you perform CMake build in) to your LD_LIBRARY_PATH, so that the current version of the shared library is always available to programs that use it.
For the csh or tcsh shells, you would add something like this to your ~/.cshrc file:
setenv LD_LIBRARY_PATH ${LD_LIBRARY_PATH}:/home/sjplimp/lammps/src
Calling the LAMMPS library:
Either flavor of library (static or shared) allows one or more LAMMPS objects to be instantiated from the calling program.
When used from a C++ program, all of LAMMPS is wrapped in a LAMMPS_NS namespace; you can safely use any of its classes and methods from within the calling code, as needed.
When used from a C or Fortran program, the library has a simple C-style interface, provided in src/library.cpp and src/library.h.
See the Python library doc page for a description of the Python interface to LAMMPS, which wraps the C-style interface.
See the sample codes in examples/COUPLE/simple for examples of C++ and C and Fortran codes that invoke LAMMPS thru its library interface. Other examples in the COUPLE directory use coupling ideas discussed on the Howto couple doc page.