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- Open Access
Design disturbance attenuating controller for memristive recurrent neural networks with mixed time-varying delays
- Jianying Xiao^{1}Email author,
- Shouming Zhong^{2} and
- Fang Xu^{1}
https://doi.org/10.1186/s13662-018-1641-8
© The Author(s) 2018
- Received: 11 January 2018
- Accepted: 9 May 2018
- Published: 18 May 2018
Abstract
This paper investigates the design of disturbance attenuating controller for memristive recurrent neural networks (MRNNs) with mixed time-varying delays. By applying the combination of differential inclusions, set-valued maps and Lyapunov–Razumikhin, a feedback control law is obtained in the simple form of linear matrix inequality (LMI) to ensure disturbance attenuation of memristor-based neural networks. Finally, a numerical example is given to show the effectiveness of the proposed criteria.
Keywords
- Memristor
- Disturbance attenuating control
- Filippov
- Time-varying delays
- Lyapunov–Razumikhin Theorem
1 Introduction
It is well known that the neural networks are so important that they have been widely applied in various areas such as reconstructing moving images, signal processing, pattern recognition, optimization problems and so on (for reference, see [1–48]). During the recent years, more and more researchers have paid attention to a new model named state-dependent switching recurrent neural networks whose connection weights vary due to their states. Generally speaking, such switching neural networks have been entitled memristive neural networks or memristor-based neural networks. Therefore, let us recall the brief development of memristive neural networks in the following. In 1971, Dr. Chua (see [10]) firstly advised that a fourth basic circuit element should exist. Different from the other three elements—the resistor, the inductor, and the capacitor—the fourth one was named the memristor. According to Chua’s theory, the memristor must have important and distinctive ability. Precisely, with the rapid development of science, a prototype of the memristor had been built by some scientists from HP Labs until 2008 (see [11]). The memristor, which not only shares many properties of resistors but also shares the same unit of measurement, is a two-terminal element whose characteristic lies in its variable resistance called memristance. Memristance, depending on how much electric charge has been passed through the memristor in a special direction, is its distinctive ability. The ability contributes to its memorizing the passed quantity of electric charge. Therefore, since 2008, its potential applications have become more and more popular in many aspects such as generation computer, powerful brain-like neural computer, and so on. There is no doubt that it has initiated the worldwide concern with the emergence of the memristor (see [11–30]). For the neural networks, the first job is considering whether they are stable or not. Therefore, a lot of scholars have studied the memristive neural networks’ multitudinous stability such as asymptotical stability, global stability, and exponential stability (see [12, 13, 15, 17–20]). Moreover, as far as we know, the passivity theory plays an important role in the analysis of the stability of dynamical systems, nonlinear control, and other areas. Thus, some researchers have investigated passivity or dissipativity criteria on MRNNs (see [14, 16, 23–25, 27–30]).
On the other hand, neural networks with time-varying delays are unavoidable to subject to persistent disturbance. How to solve persistent disturbance for delayed neural networks is still an open problem. Therefore, He et al. [31] studied the problem of disturbance attenuating controller design for delayed cellular neural networks (DCNNs). In this paper, authors designed a feedback control law to guarantee disturbance attenuation for DCNNs by employing Lyapunov–Razumikhin theorem. However, firstly, this paper just discussed disturbance attenuation for delayed cellular neural networks, so the activation function was assumed only to be \(f(x(\cdot ))=0.5(|x(\cdot)+1|-|x(\cdot)-1|)\). As is well known to us, there are still Hopfield neural networks, except cellular neural networks. Both of them belong to recurrent neural networks. Thus, how to design disturbance attenuating controller for general neural networks is our first motivation. Secondly, it is noted that the results in this paper were derived for systems only with discrete delays. Another type of time delay is distributed delay. Systems with distributed delay can be applied in the modeling of feeding systems and combustion chambers in a liquid monopropellant rocket motor with pressure feeding. So, how to solve the persistent disturbance for delayed neural networks with both discrete and distributed time-varying delays remains some room to certain extent.
Motivated by the above mentioned discussion, the problem of disturbance attenuating controller design is extended for memristor-based neural networks. To the best of our knowledge, there has not been any paper to discuss the disturbance attenuating controller design for MRNNs, which motivates our study. Our objective is to give an effective feedback control law to ensure disturbance attenuation and obtain a description of the bounded attractor set for MRNNs with mixed time-varying delays. The main contribution of this paper lies in the following aspects: first of all, this paper is the first one to investigate the disturbance attenuating controller for MRNNs, which is sure to strengthen the systematic research theory for MRNNs and must further enrich the basis of application for MRNNs. Then, comparing to the existing paper [31] about the disturbance attenuating controller design, the studied systems not only contain the more general activation functions but also include both discrete time-varying delay and distribute time-varying delays;a feedback control law is designed in the simple form of linear matrix inequality (LMI) to ensure disturbance attenuation of memristor-based neural networks by employing multiple theories such as differential inclusions, set-valued maps, and Lyapunov–Razumikhin.
2 Problem statement and preliminaries
Throughout this paper, solutions of all the systems considered in the following are intended in Filippov’s sense (see [1, 36]). \([\cdot ,\cdot]\) represents the interval. The superscripts ‘−1’ and ‘T’ stand for the inverse and transpose of a matrix, respectively. \(P>0\) (\(P\geqslant0\), \(P<0\), \(P\leqslant0\)) means that the matrix P is symmetric positive definite (positive-semi definite, negative definite, and negative-semi definite). \(\Vert\cdot\Vert\) refers to the Euclidean vector norm. \(R^{n}\) denotes an n-dimensional Euclidean space. \(\mathcal{C}([-\rho,0],R^{n})\) represents a Banach space of all continuous functions. \(R^{{m}\times{n}}\) is the set of \(m\times n\) real matrices. ∗ denotes the symmetric block in a symmetric matrix. For matrices \(\mathcal{M}=(m_{ij})_{m\times{n}}\), \(\mathcal {N}=(n_{ij})_{m\times{n}}\), \(\mathcal{M}\gg\mathcal{N}\) (\(\mathcal{M}\ll \mathcal{N}\)) means that \(m_{ij}\gg{n}_{ij}\) (\(m_{ij}\ll{n}_{ij}\)) for \(i=1,2,\ldots,m\), \(j=1,2,\ldots,n\). And by the interval matrix \([\mathcal {M},\mathcal{N}]\), it follows that \(\mathcal{M}\ll\mathcal{N}\). For \(\forall\mathcal{L}=(l_{ij})_{m\times{n}}\in[\mathcal{M},\mathcal{N}]\), it means \(\mathcal{M}\ll\mathcal{L}\ll\mathcal{N}\), i.e., \(m_{ij}\lll _{ij}\ll{n}_{ij}\) for \(i=1,2,\ldots,m\), \(j=1,2,\ldots,n\). \(\operatorname{co}\{\Pi_{1},\Pi _{2}\}\) denotes the closure of the convex hull generated by real numbers \(\Pi_{1}\) and \(\Pi_{2}\). Let \(\bar{a}_{i}=\max\{\hat{a}_{i},\check{a}_{i}\} \), \(\underline{a}_{i}=\min\{\hat{a}_{i},\check{a}_{i}\}\), \(\bar {b}_{ij}=\max\{\hat{b}_{ij},\check{a}_{ij}\}\), \(\underline{b}_{ij}=\min \{\hat{b}_{ij},\check{b}_{ij}\}\), \(\bar{c}_{ij}=\max\{\hat {c}_{ij},\check{c}_{ij}\}\), \(\underline{c}_{ij}=\min\{\hat {c}_{ij},\check{c}_{ij}\}\), \(\bar{d}_{ij}=\max\{\hat{d}_{ij},\check {d}_{ij}\}\), \(\underline{d}_{ij}=\min\{\hat{d}_{ij},\check{d}_{ij}\}\). Matrix dimensions, if not explicitly stated, are assumed to be compatible with algebraic operations.
Remark 2.1
The clear exposition about the relation between memristances and coefficients of switching system (1) has been given in the works [12, 18]. Thus, researchers can consult [12, 18] to get more information.
From the above description, the studied networks are state-dependent switching recurrent neural networks whose connection weights vary according to their states. To translate these state-dependent neural networks into the general ones, the next definitions are necessary.
Definition 2.1
Let \(E\subseteq{R}^{n}\), \(x\mapsto {F}(x)\) is called a set-valued map from \(E\hookrightarrow{R}^{n}\) if, for each point x of a set \(E\subseteq{R}^{n}\), there corresponds a nonempty set \(F(x)\subseteq{R}^{n}\).
Definition 2.2
A set-valued map F with nonempty values is said to be upper semi-continuous at \(x_{0}\in{E}\subseteq{R}^{n}\) if, for any open set N containing \(F(x_{0})\), there exists a neighborhood M of \(x_{0}\) such that \(F(M)\subseteq{N}\). \(F(x)\) is said to have a closed (convex, compact) image if, for each \(x\in{E}\), \(F(x)\) is closed (convex, compact).
Definition 2.3
Clearly, \(\operatorname{co}\{\hat{a_{i}},\check{a_{i}}\}=[\bar{a},\underline{a}]\), \(\operatorname{co}\{ \hat{b}_{ij},\check{b}_{ij}\}=[\bar{b}_{ij},\underline{b}_{ij}]\), \(\operatorname{co}\{ \hat{c}_{ij},\check{c}_{ij}\}=[\bar{c}_{ij},\underline{c}_{ij}]\), \(\operatorname{co}\{ \hat{d}_{ij},\check{d}_{ij}\}=[\bar{d}_{ij},\underline{d}_{ij}]\) for \(i,j=1,2,\ldots,n\).
Clearly, \(\operatorname{co}\{\hat{D},\check{D}\}=[\bar{D},\underline{D}]\), \(\operatorname{co}\{\hat {A},\check{A}\}=[\bar{A},\underline{A}]\), \(\operatorname{co}\{\hat{B},\check{B}\}=[\bar {B},\underline{B}]\), \(\operatorname{co}\{\hat{C},\check{C}\}=[\bar{C},\underline {C}]\), where \(\bar{A}=(\bar{a_{i}})_{n\times{n}}\), \(\underline{A}=(\underline {a}_{i})_{n\times{n}}\), \(\bar{B}=(\bar{b}_{ij})_{n\times{n}}\), \(\underline {B}=(\underline{b}_{ij})_{n\times{n}}\), \(\bar{C}=(\bar{c}_{ij})_{n\times {n}}\), \(\underline{C}=(\underline{c}_{ij})_{n\times{n}}\), \(\bar{D}=(\bar {d}_{ij})_{n\times{n}}\), \(\underline{D}=(\underline{d}_{ij})_{n\times{n}}\).
Moreover, throughout this paper, the neuron activation functions are assumed to satisfy the following assumption.
Assumption 2.1
To get the main results in this paper, the definition of disturbance attenuation is introduced as follows.
Definition 2.4
Remark 2.2
The attractor of systems (7) is the invariant set Ω, which not only lies in the fact that all the trajectories beginning from it will retain in it for any \(h\in {\mathcal{H}}\), but also subjects to the condition that any trajectories beginning from outside the set will ultimately go into the set for any \(h\in\mathcal{H}\).
To establish the feedback controller for systems (7), the following lemmas will be used in this paper.
Lemma 2.1
(Lyapunov–Razumikhin theorem [35])
- (1)
\(u( \Vert x \Vert )\leq{V}(x)\leq\nu( \Vert x \Vert )\);
- (2)
\(\dot{V}(x(t))\leq-w( \Vert x \Vert )\), if \(V(x(t+ \theta ))< p (V (x(t) ) )\).
Lemma 2.2
([27])
3 Main results
In this paper, the disturbance attenuation is investigated for memristive recurrent neural networks with mixed time-varying delays. According to Definition 2.4, the condition is constructed for the global asymptotic stability of systems (7) when \(h(t)=0\). Secondly, it is proved that there exists a bounded attractor for systems (7) when \(h(t)\neq0\). For convenience, denote \(L=\operatorname{diag}\{ l_{1},l_{2},\ldots,l_{n}\}\).
Theorem 3.1
Proof
Theorem 3.2
Proof
Remark 3.1
In comparison to the published paper [31], our paper’s contribution lies in three aspects: Firstly, the studied memristive neural networks are more popular at present; secondly, the activation function is not needed to be strict to be \(f(x(\cdot))=0.5(|x(\cdot)+1|-|x(\cdot)-1|)\), but rather it is relaxed to just satisfy Lipschitz conditions; thirdly, the discussed model not only contains discrete time-varying delay but also includes distributed time-varying delay. Therefore, our results are more general to be well applied.
Remark 3.2
Recently, many scholars have studied different kinds of control theories about MRNNS such as exponential synchronization control [12], finite-time synchronization control [13], exponential lag adaptive synchronization control [18], lag synchronization control [19], and so on. However, to the best of our knowledge, there has not been any paper to discuss the disturbance attenuating controller design for MRNNs. This paper is the first one to investigate the disturbance attenuating controller for MRNNs, which is sure to strengthen the systematic research theory for MRNNs and must further enrich the basis of application for MRNNs.
4 Numerical examples
In this section, one example is presented to demonstrate the effectiveness of our results.
Example 4.1
Remark 4.1
Comparatively speaking, although the feedback controller law is established in the form of bilinear matrix inequality (BMI), it can be easily solved by alternatively fixing some parameters and optimizing the rest. However, the LMIs in [31] are at least four, which is obviously difficult to be solved.
5 Conclusions
In this paper, the famous differential inclusions, set-valued maps, and Lyapunov–Razumikhin are employed to design a feedback controller law for MRNNs. A feedback controller law is obtained with less computation burden. In the future, other approach, such as the delay-partitioning technique, can be employed to further reduce the conservativeness of the obtained result.
Declarations
Acknowledgements
This work was supported in part by the National Science Foundation of China under Grant 61202045, Grant 11501475,Grant 61703060, in part by the Science and Technology Innovation Team of Education Department of Sichuan for Dynamical System and its Applications (No. 18TD0013),and in part by the Program of Science and Technology of Sichuan Province of China under Grant No. 2016JY0067.
Authors’ contributions
All authors contributed equally to the writing of this paper. All authors read and approved the manuscript.
Competing interests
The authors declare that they have no competing interests.
Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
Authors’ Affiliations
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