A discrete-time time-invariant linear system (DILS) is considered which has resulted from the discretization of a continuous-time time-invariant linear system (CILS) by the zero order hold. In this system, the system and input matrices are given by exp(AT) and $ whereAandBare the system and input matrices of the CILS, andTis a sampling interval. Since they involve the matrix exponential, their computations are not easy.