Hindawi Publishing Corporation Journal of Applied Mathematics Volume 2012, Article ID 523812, 12 pages doi:10.1155/2012/523812 Research Article LMI Approach to Stability Analysis of Cohen-Grossberg Neural Networks with p-Laplace Diffusion Xiongrui Wang,1, 2 Ruofeng Rao,1, 2 and Shouming Zhong2, 3 1 Department of Mathematics, Yibin University, Yibin 644007, China Institute of Mathematics, Yibin University, Yibin 644007, China 3 College of Applied Mathematics, University of Electronic Science and Technology of China, Chengdu 610054, China 2 Correspondence should be addressed to Ruofeng Rao, ruofengrao@163.com Received 1 August 2012; Revised 24 October 2012; Accepted 12 November 2012 Academic Editor: Zhilong L. Huang Copyright q 2012 Xiongrui Wang et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The nonlinear p-Laplace diffusion p > 1 was considered in the Cohen-Grossberg neural network CGNN, and a new linear matrix inequalities LMI criterion is obtained, which ensures the equilibrium of CGNN is stochastically exponentially stable. Note that , if p 2, p-Laplace diffusion is just the conventional Laplace diffusion in many previous literatures. And it is worth mentioning that even if p 2, the new criterion improves some recent ones due to computational efficiency. In addition, the resulting criterion has advantages over some previous ones in that both the impulsive assumption and diffusion simulation are more natural than those of some recent literatures. 1. Introduction and Preparation It is well known that Cohen-Grossbeg neural network CGNN was proposed by Cohen and Grossberg 1 in 1983. Since then there have been a lot of interested results obtained in many literatures see 2–9 due to its general applications, such as pattern recognition, image and signal processing, optimization automatic control, and artificial intelligence. Usually, there exist the impulsive effect and time-varying delays phenomenon in various neural networks 3, 5–7, 10–14. Besides, diffusion effects cannot be avoided in the neural networks when electrons are moving in asymmetric electromagnetic fields 15–18. However, diffusion disturbance was always simulated simply by linear Laplace diffusion 15–18. Few papers 2 Journal of Applied Mathematics involved the nonlinear reaction-diffusion 19. So in this paper, we investigate the stability of the following stochastic CGNN with nonlinear p-Laplace diffusion p > 1: x, u ◦ ∇p u − Aut, x dut, x ∇ · Dt, × But, x − Cfut, x Dgut − τt, x dt σut, xdwt, t ∈ tk , tk1 u tk , x Mu t− , x , t tk ut0 θ, x ϕθ, x, ∂ui t, x 0, ∂ν 1.1 θ, x ∈ −τ, 0 × ∂Ω t, x ∈ −τ, ∞ × ∂Ω, i 1, 2, . . . , n, where Ω is a bounded subset in Rm with smooth boundary ∂Ω, and ∂ui t, x/∂ν ∂ui t, x/∂x1 , ∂ui t, x/∂x2 , . . . , ∂ui t, x/∂xm T denotes the outward normal derivative on ∂Ω. Remark 1.1. If p 2, system 1.1 was studied by 5 though there is a little difference between Dirichlet boundary condition and Neumann boundary condition. However, our impulsive assumption utk , x Mut−k , x is more natural than that of 5, which will result in some difference in methods. Here, M is a diagonal matrix, Ω ∈ Rm is a bounded compact set with smooth boundary, u u1 , u2 , . . . , un T ∈ Rn , and wt w1 t, w2 t, . . . , wn tT is a n-dimensional Brownian motion defined on a complete probability space Ω, F, P with the natural filtration {Ft }t≥0 generated by the process {ws : 0 ≤ s ≤ t}. We associate Ω with the canonical space generated by all {wi t} and denoted by F the associated σ-algebra generated by wt with the probability measure p. Aut, x presents an amplification function, But, x is an appropriately behavior function, and f and g denote the activation function. τt 0 ≤ τt ≤ τ corresponds to the transmission delays at time, and tk is called the impulsive moment with 0 < t1 < t2 < · · · < tk < · · · and limk → ∞ tk ∞. We always assume utk , x ◦ utk , x. ∇p u ∇p u1 , . . . , ∇p un T , ∇p ui |∇ui |p−2 ∂ui /∂x1 , . . . , |∇ui |p−2 ∂ui /∂xm T , D p−2 ik |∇ui | ∂ui /∂xk n×m is Hadamard product of matrix D and ∇p u 20. Here, ∇p u D ik n×m . Let Yi the diffusion parameters matrix Dt, x, u is denoted simply as D D T T yi1 , . . . , yim , i 1, 2, . . . , n, and matrix Y Y1 , . . . , Yn , and we denote ∇ · Yi m T k1 ∂yik /∂xk , ∇ · Y ∇ · Y1 , ∇ · Y2 , . . . , ∇ · Yn . Particularly, ∇p u ∇u for the case of p 2. Remark 1.2. Diffusion effects always occur in the neural networks when electrons are moving in asymmetric electromagnetic fields 15–18, and diffusion behavior is so complicated that it cannot always be simulated by linear Laplace diffusion. So in this paper, the nonlinear p-Laplace diffusion is considered in System 1.1. Journal of Applied Mathematics 3 Assume, in addition, the following. H1 Aut, x is a bounded, positive, and continuous diagonal matrix, that is, there exist two positive diagonal matrices A and A such that 0 < A ≤ Aut, x ≤ A. H2 But, x b1 u1 t, x, b2 u2 t, x, . . . , bn un t, xT such that there exists a positive diagonal matrix B diagB1 , B2 , . . . , Bn satisfying bi ui t, x/ui t, x ≥ Bi for all i. H3 There exist two positive diagonal matrices F diagF1 , F2 , . . . , Fn and G diagG1 , G2 , . . . , Gn such that 0≤ fi r ≤ Fi , r 0≤ gi r ≤ Gi , r ∀i. 1.2 H4 The null solution is the equilibrium point of system 1.1, that is, the following conditions hold: B0 − Cf0 − Dg0 0, trace σ T ut, xσut, x ≤ uT t, xQut, x, 1.3 where the symmetrical matrix Q > 0. For convenience’s sake, we introduce some standard notations i L2 RR × Ω: the space of real Lebesgue measurable functions of R × Ω, it is a Banach space for the 2-norm ut 2 ni1 ui t 1/2 with ui t Ω |ui t, x|2 dx1/2 , where |ui t, x| is Euclid norm. ii L2F0 −τ, 0 × Ω; Rn : the family of all F0 -measurable C−τ, 0 × Ω; Rn - value random variable ξ {ξθ, x : −τ ≤ θ ≤ 0, x ∈ Ω} such that sup−τ≤θ≤0 E ξθ 22 < ∞, where E{·} stands for the mathematical expectation operator with respect to the given probability measure p. iii Q qij n×n > 0 <0: a positive negative definite symmetrical matrix, that is, yT Qy > 0 <0 for any 0 / y ∈ Rn . iv Q qij n×n ≥ 0 ≤0: a semipositive semi-negative definite symmetrical matrix, that is, yT Qy ≥ 0 ≤0 for any y ∈ Rn . Q ≤ Q: this means Q − Q is a semi-positive semi-negative symmetrical v Q ≥ Q definite matrix. Q < Q: this means Q − Q is a positive negative symmetrical definite vi Q > Q matrix. vii λmax Φ, λmin Φ denotes the largest and smallest eigenvalue of symmetrical matrix Φ, respectively. viii I: identity matrix with compatible dimension. ix Denote |C| |cij |n×n for any matrix Cn×n ; |ut, x| |u1 |, |u2 |, . . . , |un | for any u ∈ Rn . Let ut, x; ϕ denote the state trajectory from the initial data ut0 θ, x; ϕ ϕθ, x on −τ ≤ θ ≤ 0 in L2F0 −τ, 0 × Ω; Rn . 4 Journal of Applied Mathematics Definition 1.3. The null solution of impulsive system 2.2 is globally stochastically exponentially stable in the mean square if for every ϕ ∈ L2F0 −τ, 0 × Ω; Rn , there exists scalars β > 0 and γ > 0 such that 2 2 E u t, ϕ 2 ≤ γe−βt sup E ϕθ2 . 1.4 −τ≤θ≤0 Lemma 1.4 see 11. Let U, P be any matrices, ε > 0 is a positive number and matrix H H T > 0, then P T U UT P ≤ εP T HP ε−1 UT H −1 U. 1.5 Lemma 1.5 Schur complement 3. The LMI Qt St ST t Rt 1.6 > 0, where matrix St and symmetrical matrices Qt and Rt depend on t, is equivalent to any one of the following conditions: L1 Rt > 0, Qt − StR−1 tST t > 0; L2 Qt > 0, Rt − ST tQ−1 tST t > 0. Lemma 1.6 see 21. Consider the following differential inequality: D vt ≤ −avt bvtτ , t / tk − − vtk ≤ ak v tk bk v tk τ , 1.7 where vt ≥ 0, vtk τ supt−τ≤s≤t vs, vt−k τ supt−τ≤s≤t vs and vt is continuous except tk , k 1, 2, . . ., where it has jump discontinuities. The sequence tk satisfies 0 t0 < t1 < t2 < · · · < tk < tk1 < · · · , and limk → ∞ tk ∞. Suppose that 1 a > b ≥ 0; 2 tk − tk−1 > δτ, where δ > 1, and there exist constants γ > 0, M > 0 such that ρ1 ρ2 · · · ρk1 ≤ Meγtk , 1.8 where ρi max{1, ai bi eλτ }, λ > 0 is the unique solution of equation λ a − beλτ then vt ≤ Mv0τ e−λ−γt . 1.9 In addition, if θ supk∈Z {1, ak bk eλτ }, then vt θv0τ e−λ−lnθe λτ /δτt , t ≥ 0. Computer simulation is shown in Figures 1, 2, 3, and 4. 1.10 Journal of Applied Mathematics 5 0.2 0.18 0.16 0.14 0.12 u1 0.1 0.08 0.06 0.04 0.02 0 0 5 1 15 10 0.5 ce: Spa Time: t 0 x Figure 1: Computer simulation of the state u1 t, x . 0.18 0.16 0.14 u1 (t, 0.259) 0.12 0.1 0.08 0.06 0.04 0.02 0 0 5 10 15 Figure 2: Sectional curve of the state variable u1 t, x . 2. Main Results Theorem 2.1. If assumptions (H1)–(H4) hold, in addition, the following conditions are satisfied: C1 there exists diagonal matrices P1 diagp11 , p12 , . . . , p1n > 0 and P2 > 0 such that ⎛ −2P1 AB F 2 P1 Q P2 T ⎜ C AP ⎝ T 1 D AP1 P1 A|C| −I 0 ⎞ P1 A|D| ⎟ 0 ⎠ < 0; −I 2.1 C2 min{λmin Θ/λmax P1 , 1 − μ} > λmax G2 /λmin P2 ≥ 0, where Θ 2P1 AB − P1 A|C||C|T AP1 − P1 A|D||D|T AP1 − F 2 − P1 Q − P2 , where τ t ≤ μ < 1 for all t; 6 Journal of Applied Mathematics 0.02 0.018 0.016 0.014 u2 0.012 0.01 0.008 0.006 0.004 0.002 0 1 0.5 0 ce: x 5 Spa 10 15 Time: t Figure 3: Computer simulation of the state u2 t, x . 0.02 0.018 u2 (t, 0.267) 0.016 0.014 0.012 0.01 0.008 0.006 0.004 0.002 0 0 5 10 15 Figure 4: Sectional curve of the state variable u2 t, x . C3 there exists a constant δ > 1 such that infk∈Z tk − tk−1 > δτ, δ2 τ > lnρeλτ and λ − lnρeλτ /δτ > 0, where λ > 0 is the unique solution of the equation λ a − beλτ , and ρ max{1, λmax MP1 M/λmin P1 eλτ }, a min{λmin Θ/λmax P1 , 1 − μ}, b λmax G2 /λmin P2 , then the null solution of system 1.1 is stochastically exponentially stable with convergence rate 1/2λ − lnρeλτ /δτ. Proof. First, we can get by Guass formula see 20, Lemma 2.3 Ω x, u ◦ ∇p u dx uT P1 ∇ · Dt, T m m ∂ ∂ p−2 ∂u1 p−2 ∂un u P1 dx D1k |∇u1 | ,..., Dnk |∇un | ∂xk ∂xk ∂xk ∂xk Ω k1 k1 T Journal of Applied Mathematics n m p−2 ∂uj ∂ dx p1j uj Djk ∇uj ∂xk ∂xk Ω j1 k1 m n − Ω k1 j1 jk ∇uj p−2 p1j D ∂uj ∂xk 7 2 dx. 2.2 Construct the Lyapunov functional as follows: V V1 V2 , 2.3 where V1 u t, xP1 ut, xdx uT t, xP1 |ut, x|dx T Ω V2 Ω t Ω u s, xP2 us, xds dx. T t−τt Then LV1 Ω − m n jk ∇uj p−2 2p1j D k1 j1 ∂uj ∂xk 2 dx −2 2 2 Ω Ω Ω Ω uT t, xP1 Aut, xBut, xdx uT t, xP1 Aut, xCfut, xdx uT t, xP1 Aut, xDgut − τt, xdx trace σ T ut, xP1 σut, x dx ≤ − 2 uT t, xP1 AB|ut, x|dx Ω T u t, xP1 A|C||C|T AP1 |ut, x| f T ut, xfut, x dx Ω T u t, xP1 A|D||D|T AP |ut, x| g T ut − τt, xgut − τt, x dx Ω Ω uT t, xP1 Qut, xdx 2.4 8 Journal of Applied Mathematics ≤ − uT t, x 2P1 AB − P1 A|C||C|T AP1 − P1 A|D||D|T AP1 − F 2 − P1 Q |ut, x|dx Ω Ω uT t − τt, xG2 ut − τt, xdx uT t, xP2 ut, x − 1 − τ t uT t − τtP2 ut − τt dx LV2 Ω T ≤ uT t − τtP2 ut − τtdx. u t, xP2 |ut, x|dx μ − 1 Ω Ω 2.5 And then we have LV ≤ − T x|dx uT t − τt, x G2 μ − 1 P2 ut − τt, xdx. x t, Θ|ut, u Ω Ω 2.6 Next, we use the method similar as that of 22. Since ut, x is the solution of system, o formula and V ut, x ∈ C2 Rm , R for all t, we can get by It V t V tk t LV us, xds tk t tk ∂V σus, xdws. ∂u 2.7 Then we have EV ut, x EV utk , x t ELV s, xds, t ∈ tk , tk1 . 2.8 tk Thus, for small enough Δt > 0, we have EV ut Δt, x EV utk , x tΔt ELV s, xds, t ∈ tk , tk1 , 2.9 tk and then EV ut Δt, x − EV ut, x tΔt ELV s, xds t tΔt − uT s, xΘ|us, x|dx ≤E Ω t 2 u s − τs, x G μ − 1 P2 us − τs, xdx ds, T Ω 2.10 t ∈ tk , tk1 . Journal of Applied Mathematics 9 Since T uT t − τt, x 1 − μ P2 ut − τt, xdx u t, xΘ|ut, x|dx Ω Ω λmin Θ T uT t − τt, xP2 ut − τt, xdx ≥ u t, xP1 |ut, x|dx 1 − μ λmax P1 Ω Ω ! λmin Θ , 1−μ V ≥ min λmax P1 λmax G2 uT t − τt, xG2 ut − τt, xdx ≤ uT t − τt, xP2 ut − τt, xdx, λmin P2 Ω Ω 2.11 Then, ! λmin Θ λmax G2 D EV ut, x ≤ − min , 1 − μ EV t EV tτ , λmax P1 λmin P2 t ∈ tk , tk1 . 2.12 Next, we have V tk u tk , xP1 utk , xdx T Ω ≤ Ω u T t−k , x Ω uT tk − τtk , xP2 utk − τtk , xdx MP1 Mu t−k , x dx Ω uT tk − τtk , xP2 utk − τtk , xdx 2.13 λmax MP1 M − − V tk V t k τ . λmin P1 Now the conditions C1–C3 and Lemma 1.6 deduce EV t ≤ ρV 0τ e−λ−lnρe λτ /δτt 2.14 or 2 −λ−lnρeλτ /δτt λmax P sup E φs 2 e ρ λmin P −τ≤s≤0 2 E ut, x ≤ 2.15 which together with Definition 1.3 implies the accomplishment of the proof. Remark 2.2. The nonlinear p-Laplace diffusion p > 1 brings a great difficulties in judging the stability. However, even if p 2, Theorem 2.1 has more computational efficiency than 15, Theorem 3.1 due to LMI criterion. 10 Journal of Applied Mathematics 3. Examples Consider the following impulsive CGNN: dut, x 0 0.0005 0 1.65 0.5 sin u1 ◦ ∇p u − 0 1.58 0.5 sin u2 0 0.0005 5.19u1 − 0.02u1 cos u1 0.1 −0.03 × − fut, x 5.18u2 − 0.01u2 cos u2 −0.03 0.1 ! 0.1 −0.03 − gut − τt, x dt σut, xdwt, t ∈ tk , tk1 −0.03 0.1 1.350 0 u tk u t− , x , t tk 0 1.350 ∇· ut0 θ, x φθ, x, ∂ui t, x 0, ∂ν where Ω {x1 , x2 T ∈ R2 | − F √ θ, x ∈ −0.65, 0 × ∂Ω t, x ∈ −τ, ∞ × ∂Ω, 3.1 2 ≤ x1 , x2 ≤ 0.100 0 0 0.100 i 1, 2, √ 2}, and the corresponding matrices G, Q 0.0001 0 . 0 0.0001 3.2 We might as well assume that t0 0, tk − tk−1 0.525, τt 0.65, τ t ≤ μ 0.99 for all t ≥ t0 , and ⎛ ⎞ |u1 1| − |u1 − 1| ⎜ ⎟ 20 ⎟ fu gu ⎜ ⎝ |u2 1| − |u2 − 1| ⎠, 20 x1 − cos5πxcos189 x − 0.25e−100s , −0.65 ≤ s ≤ 0, 1 − xsin2 4πxcos201 x − 0.55e−100s 1 0 2 0 5.160 0 A A , , B . 0 1 0 2 0 5.160 φs, x 3.3 By way of MATLAB LMI Control Toolbox, we can solve the LMI condition in C1 and get P1 0.2392 0 , 0 0.2392 1.2291 0 P2 . 0 1.2291 3.4 Next, we will prove that such P1 and P2 make C2 and C3 hold. Indeed, by computing directly, we can obtain a 0.01, b 0.0081, and then C2 holds. Moreover, we might as well Journal of Applied Mathematics 11 assume δ 82, and then we have λ 0.0019, ρ 2.8235, thus C3 is satisfied. Now from Theorem 2.1 we can compute the convergence 9.3809 ∗ 10−0.004 . 4. Conclusions In this paper, we investigate the influence of impulse, time-delays and diffusion behaviors on the stability of stochastic Cohen-Grossberg neural network CGNN. The LMI conditions of stochastic exponential stability of impulsive CGNN with p-Laplace reaction-diffusion terms was given, and an illustrate example was also given to show the effectiveness of the obtained result. Besides, the result obtained in this paper is also valid to the Laplace reaction-diffusion in the case of p 2 and has more computational efficiency due to the LMI approach even if p 2 Remark 2.2. 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