Project compile even without linear algebra

src/FiniteDifference/Derivative.hpp

src/FiniteDifference/FDScheme.hpp

src/Makefile.am

src/Matrix/SparseMatrix.hpp

src/Solvers/umfpack_solver.hpp

src/Vector/Vector.hpp

src/Vector/Vector_eigen.hpp

src/Vector/Vector_eigen_util.hpp

src/Vector/Vector_unit_tests.hpp

src/util/grid_dist_testing.hpp

src/util/util_num.hpp