This directory has a small collection of routines, useful for exchanging data between 2 codes being run together as a coupled application. It is used by the LAMMPS <-> Quest and LAMMPS <-> SPPARKS applications in 2 sister directories. The library dir has a Makefile (which you may need to edit for your box). If you type g++ -f Makefile.g++ you should create libcouple.a, which the other coupled applications link to. Note that the library uses MPI, so the Makefile you use needs to include a path to the MPI include file, if it is not someplace the compiler will find it.