On the Lipschitz continuity of derivatives for some scalar nonlinearities

Vector nonlinearities determined by a scalar function arise in various mathematical models. The numerical solution of the corresponding partial differential equations often rely on the Lipschitz continuity of the derivative of the nonlinear operator. In this paper a simple sufficient condition is given for the required Lipschitz continuity, also providing an easily computable estimate of the Lipschitz constant. Some discussion is included for the corresponding elliptic operators.