On smoothing and order reduction effects for implicit Runge-Kutta formulae

Abstract It is well known that many important classes of Runge—Kutta methods suffer an order reduction phenomenon when applied to certain classes of stiff problems. In particular, the s-stage Gauss methods with stage order s and order of consistency 2s behave like methods of order s when applied to the class of singularly perturbed problems. In this paper we will show that the process of smoothing can ameliorate this effect, when dealing with initial-value problems, by first studying the effect of smoothing on the standard Prothero—Robinson problem and then by extending the analysis to the general class of singularly perturbed problems.