“…In the case of NBCs, properties of discrete SLP (dSLP) were investigated in [1,2,5,6,13,15,22] and results were used for theoretical justification of stability Finite Difference Schemes (FDS) for various elliptic, hyperbolic and parabolic equations [20,21]. Finite difference method together with asymtotic formulas for eigenvalues [26,27] gives very good approximation of spectrum for differential SLP.…”