SIAM Journal on Control and Optimization, Vol.54, No.4, 1919-1933, 2016
ALMOST SURE EXPONENTIAL STABILITY OF STOCHASTIC DIFFERENTIAL DELAY EQUATIONS
This paper is concerned with the almost sure exponential stability of the multidimensional nonlinear stochastic differential delay equation (SDDE) with variable delays of the form dx(t) = f(x(t - delta(1)(t)), t) dt broken vertical bar g(x(t - delta(2)(t)), t) dB(t), where delta(1), delta(2) : R+ -> [0, tau] stand for variable delays. We show that if the corresponding (nondelay) stochastic differential equation (SDE) dy(t) = f(y(t), t) dt + g(y(t), t) dB(t) admits a Lyapunov function (which in particular implies the almost sure exponential stability of the SDE) then there exists a positive number tau* such that the SDDE is also almost sure exponentially stable as long as the delay is bounded by tau*. We provide an implicit lower bound for tau* which can be computed numerically. Moreover, our new theory enables us to design stochastic delay feedback controls in order to stabilize unstable differential equations.
Keywords:almost sure exponential stability;stochastic differential delay equations;Ito formula;Brownian motion;stochastic stabilization