“…These investigations extend the well-known principle that closing the loop around an exponentially stable, linear, "nite-dimensional, continuous-time, single-input, single-output plant , with transfer function G , compensated by an integral controller with gain k, will result in a stable closed-loop system which achieves asymptotic tracking of arbitrary constant reference signals, provided that the modulus "k" of the integrator gain k is su$ciently small and kG (0)'0 (see References [5}7]). Therefore, if a plant is exponentially stable and if the sign of G (0) is known (this information can be obtained from plant step response data), then the problem of tracking by low-gain integral control reduces to that of tuning the gain parameter k. Such a controller design approach (&tuning regulator theory' [5]) has been successfully applied in process control, see, for example, References [8,9]. Furthermore, the problem of tuning the integrator gain adaptively has been addressed in various papers for "nite-dimensional [1, 10}12] and in"nite-dimensional systems [2,3,13], with input nonlinearities considered in References [2,3,11] and both input and output nonlinearities treated in Reference [1].…”