Asymptotic expansions for time-varying scalar differential equations using the residue theorem for their discretized difference equations

A fictitious time-dependent time-varying finite sampling period is defined for each time instant at which the asymptotic expansion of the solution of a continuous-time differential equation is investigated. Such a time-dependent sampling period is defined as the quotient of each time instant and a positive integer which tends to infinity as time tends to infinity. The asymptotic expansion formulas are extendable to the case of stable Lyapunov’s equations and to the use of a constant sampling period with minor modifications in the required mathematical proofs. Additional stability results are also discussed.