For compiling your files using ABACUS add the abacus/include directory either to your include directory path or specify it explicitly with the -I compiler option. Furthermore, add the include file paths of the LP-solvers you want to use. The flag for the C++ compiler can be defined at compilation time using the -D switch of the compiler (e.g., -DABACUS_COMPILER_GCC41) or specified in the Makefile. See table 2.1 for valid settings. It might be helpful to consult the Makefile of the example included in the ABACUS distribution.