MS-stability of the Euler–Maruyama method for stochastic differential delay equations

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Abstract

The aim of this paper is to investigate the stability of the Euler–Maruyama method for the stochastic differential equations with time delay. The definition of MS-stability of numerical methods is established. The condition of the mean square stability of analytical solution is obtained for a linear scalar system with multiplicative noise, and the MS-stability of the numerical scheme is proved.

Introduction

Many of the processes, both natural and man-made, involve time delays. That is, the future state of the system is dependent on some of the past history. Indeed, the stochastic differential delay equations (SDDEs) as the stochastic models appear frequently in applied research, and the related study has received considerable attention. For example, the theory of existence and uniqueness of the solution can be found in [9], [13], and the stability of SDDEs has studied by Kolmanovskii and Myshkis [5], Liu and Xia [8], Mao [9], [10]. Moreover, some new results on the exponential stability were established for the SDDEs in [11].

The general form of the SDDEs isdX(t)=f(t,X(t),X(t−τ))dt+g(t,X(t),X(t−τ))dW(t),t⩾0,X(t)=ψ(t),t∈[−τ,0],where τ is a positive fixed delay, W(t) is a d-dimensional standard Wiener process and ψ(t) is a C([−τ,0];Rm)-valued initial segment, and the functions f:R+×Rm×RmRm, g:R+×Rm×RmRm×d.

Explicit solutions can hardly be obtained for the SDDEs. Thus, it is necessary to develop appropriate numerical methods and to study the properties of these approximate schemes. The convergence and stability properties of the numerical methods for the stochastic ordinary differential equations (SODEs) have been studied by many authors, for instance, Burrage [2], Higham [3], Kloeden and Platen [4], Milstein [12], Saito and Mitsui [14], [15], Tian and Burrage [16]. But the study of numerical scheme for SDDEs is less by far. Concerning the convergence properties, we refer to [1], [6], [7]. However there is no result for the stability of numerical schemes for the SDDEs.

In this paper, we focus on the stability of the Euler–Maruyama numerical solutions for a scalar test equation of the formdX(t)=[aX(t)+bX(t−τ)]dt+cX(t−τ)dW(t),t⩾0,X(t)=ψ(t),t∈[−τ,0].where a,b,c∈R. The main aim of our paper is to show that the Euler–Maruyama method applied to Eq. (2) is mean square stable under the condition which guarantees the stability of the analytical solution.

In Section 2 we will introduce some necessary notations and assumptions. The condition of the mean square stability of Eq. (2) will be established. In Section 3, the Euler–Maruyama method will be used to produce the numerical solutions. Furthermore, our main result will be shown and proved in this section. We will provide some numerical examples in Section 4.

Section snippets

Mean square stability of analytical solution

Let (Ω,F,P) be a filtered probability space with a filtration (Ft)t⩾0, which satisfies the usual condition. Let W(t), t⩾0 in Eqs. , be Ft-adapted and independent of F0. Moreover, |·| is the Euclidean norm in Rm and the matrix norm of matrix g is defined by ∥g∥=sup{|gx|:|x=1|}. We assume the initial segment ψ(t), t∈[−τ,0] to be F0-measurable and right continuous, Eψ2<∞, where ∥ψ∥=supτt⩽0|ψ(t)|. Further, we let f(t,0,0)=g(t,0,0)≡0. To ensure the existence and uniqueness of the solution, we

Numerical stability analysis

Apply the Euler–Maruyama method to Eq. (2), then we haveXn+1=Xn+(aXn+bXn−m)h+cXn−mΔWn,where h is the stepsize which satisfies τ=mh for an integer number m, and tn=nh, Xn=X(tn), when tn⩽0, we have Xn=ψ(tn). Moreover, the increments ΔWn:=W(tn+1)−W(tn) are independent N(0,h)-distributed Gaussian random variables. We assume Xn to be Ftn-measurable at the mesh-points tn.

Definition 3

Under the condition (7), a numerical method applied to Eq. (2) is said to be MS-stable, if there exists a h0(a,b,c)>0, such that

Numerical examples

We use the equationdX(t)=[aX(t)+bX(t−1)]dt+cX(t−1)dW(t)as a test equation, and take ψ(t)=t+1 for t∈[−τ,0] as an initial function, which is used to compute the solution on t∈[0,1], that isX(t)=e0tadsψ(0)+∫0tbψ(s−1)e−∫0sadrds+∫0tcψ(s−1)e−∫0sadrdW(s)=eat1+ba2ba2bat+ceat0tse−asdW(s).We obtain the explicit solution on the second interval [1,2] by using the above solution as the new initial function. In fact, on every interval the computing method is the same as the method for SODEs. We compute

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    The state-of-the-art of studying the numerical stability for stochastic differential equations (SDEs) could be found in [13,14]. In the case of SDDE, the mean-square stability of Euler–Maruyama and Milstein methods have been respectively developed in [15,16]. The rest of paper proceeds as follows.

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This work is supported by the NSF of PR China (no. 10271036).

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