- 1Jiangsu Collaborative Innovation Center of Atmospheric Environment and Equipment Technology (CICAEET) Nanjing University of Information Science and Technology, Nanjing, China
- 2School of Artificial Intelligence, Nanjing University of Information Science and Technology, Nanjing, China
- 3Collaborative Innovation Center of Memristive Computing Application (CICMCA), Qilu Institute of Technology, Jinan, China
A variable boostable chaotic system and the Hindmarsh–Rose neuron model are applied for observing the dynamics revised by memristive computation. Nonlinearity hidden in a memristor makes a dynamic system prone to be chaos. Inherent dynamics in a dynamic system can be preserved in specific circumstances. Specifically, as an example, offset boosting in the original system is inherited in the derived memristive system, where the average value of the system variable is rescaled linearly by the offset booster. Additional feedback from memristive computation raises chaos, as a case, in the Hindmarsh–Rose neuron model the spiking behavior of membrane potential exhibits chaos with a relatively large parameter region of the memristor.
Introduction
Memristor is a new nonlinear component that brings great convivence for chaos generation [1–5] and dynamics control [6–10]. When a memristor is introduced, a dynamical system finds its way to exhibit more complicated evolvements. Whatever in a 3D [11–13] or 4D [14–16] or an even higher dimensional [17, 18] system, a memristor does endow abundant dynamics including hidden attractor [19, 20], bistability [21, 22], tristability [23], extreme multistability [24–27], and megamultistability [28–30]. Memristor, meminductor [31, 32], and memcapacitor [33, 34] are in fact representations of special computation, where the current output is critically associated with the past states and the current input. This is essentially a kind of time delay, which brings nonlinear factors and makes the system more prone to be chaos or even hyperchaos [35–37].
In this paper, a memristor-based computation is introduced in a variable boostable chaotic system and the Hindmarsh–Rose neuron model for observing the influence of memory from the memristive computation. As shown in Figure 1, chaos oscillation, and dynamics control are explored and discussed in a variable boostable system and neuron cells. In A 3D Memristive Chaotic System, the VB14 system is applied to host a memristor, where chaotic oscillation is preserved with the inherent property of offset boosting. The system and component parameter shows their separate power for preserving chaos and revising dynamics . In A Memristive Hindmarsh-Rose Neuron, the Hindmarsh–Rose neuron model is studied as an example to demonstrate the effect of memory. Memristive computation shows its disturbance for chaos production. Some discussion and future work are presented in the last section.
A 3D Memristive Chaotic System
Basic Analysis
A variable boostable chaotic system is a class of chaotic systems with an independent variable that can be controlled with a linearly rescaled average value. By introducing a constant, the offset of the variable can be boosted to any desired level. Thus, we can control the variable switch between a bipolar signal and a unipolar signal according to the constant. In this paper, VB14 is selected as the seed system for hosting a memristor,
when a = 3.55, b = 0.5, IC = (1, 0, 1), system (1) is chaotic with Lyapunov exponents (0.151, 0, −0.651) and Kaplan–Yorke dimension
where the flux-controlled memductance is described as,
Here y is the internal variable of the memristor and can be regarded as the flux-controlled variable of the memristor. The memristor function curve and the corresponding hysteresis loop are plotted as shown in Figure 2. In the process memristor with the internal variable determined as,
FIGURE 2. Memristor function and corresponding hysteresis loop. (A) memristor function, (B) hysteresis loop.
FIGURE 3. Strange attractor of system (2) with a = 2.4, b = 0.5, c = 1.7, d = 2.5 under initial conditions (1, 0, 1) (A) x-y plane, (B) x-z plane.
The hypervolume contraction of this system can be described by the following expression:
which is related to the values of the system variable z and parameter b. When system parameters are a = 2.4, b = 0.5, c = 1.7, and d = 2.5, the result of this equation
Let the left-hand side of the system (2) be equal to zero, the equilibria can be solved by the following equation:
system (2) has a non-zero equilibrium point S0 = (0.43564387, 0.87128774, 0.87128774). Linearizing system (2) at the equilibrium point S0, the Jacobian matrix can be obtained as,
The characteristic equation is derived as:
Therefore,
Bifurcation Observation
For system (2), the dynamic behavior of the system can be modified by changing the parameters. When b = 0.5, c = 1.7, d = 2.4 and the initial condition is (1, 0, 1), the bifurcation diagram and Lyapunov exponents of parameter a varies in [0.5, 3] are shown in Figures 4A,B. It can be seen from the figure that the system has a couple of periodic windows. When parameter a varies in the range of [0.5, 1.1], system (2) is periodic and exhibits a period-doubling process; then, the system enters a chaotic state around a = 1.1. After that system (2) remains in chaos in [1.1, 1.255], [1.4, 1.725], [1.8, 2.05], [2.1, 2.5], [2.55, 3] except a couple of interrupted period windows.
FIGURE 4. Bifurcation and Lyapunov exponents diagrams of oscillator (2) with b = 0.5, c = 1.7, d = 2.4 and the initial conditions is (1, 0, 1) when the parameter a is in [0.5, 3]. (A) bifurcation, (B) Lyapunov exponents.
When a = 2.4, c = 1.7, d = 2.5, the initial condition is (1, 0, 1) and b varies in (0, 1.5), the corresponding bifurcation and Lyapunov exponents are shown in Figure 5. From Lyapunov exponents and bifurcation, we observe that the system undergoes a typical inverse-period-doubling process from chaos. When b in [0, 0.385], [0.435, 0.735], and [0.785, 0.81], system (2) exhibits chaos. Some periodic windows such as [0.385, 0.435] are seen. When parameter b varies in [0.81, 1.5], system (2) gives cycle-4, cycle-2, and cycle-1 limit cycles.
FIGURE 5. Lyapunov exponents and bifurcation diagrams of system (2) with a = 2.4, c = 1.7, d = 2.5 and initial conditions (1, 0, 1) when the parameter b varies in [0, 1.5]. (A) bifurcation, (B) Lyapunov exponents.
To observe the memristive computation influence on system dynamics, here the coefficient d implying memristor resistance is used as a bifurcation parameter. When a = 2.4, b = 0.5, and c = 1.7, and initial condition (1, 0, 1), and d increases in the region of [0, 5], the bifurcation and Lyapunov exponents are shown in Figures 6A,B. When the internal parameter d of the memristor is in the range of [1.8, 2.01], the system shows periodic oscillation; similarly, when the internal parameter d of the memristor is in the range of [2.01, 2.71] and [2.71, 3.56], the system again turns to be chaos; when the internal parameter d of the memristor changes in the region of [3.56, 3.96], the system enters a chaotic state. A typical inverse periodic doubling bifurcation happens when d becomes larger.
FIGURE 6. Lyapunov exponents and bifurcation diagrams of system (2) with a = 2.4, b = 0.5, c = 1.7 and initial condition (1, 0, 1) when the memristor parameter d varies in [0, 5]. (A) bifurcation, (B) Lyapunov exponents.
As shown in the latter, the newly introduced memristor does not break the property of offset boosting. Suppose if there is a constant e is introduced in the last dimension,
Different constants of e revise the offset of the system variable x directly. As shown in Figure 7, three chaotic attractors with different offsets are displayed in cyan, green, and red. Here signal x(t) at e = 0 is bipolar signal, while signals at x(t) at e =
FIGURE 7. Offset boosted attractors of system (8) with a = 2.4, b = 0.5, c = 1.7,and d = 2.5: (A) attractors on plane of x-z, (B) signal x(t).
A Memristive Hindmarsh-Rose Neuron
The 2D HR neuro was simplified from the classical Hodgkin–Huxley model [25] by HR, which is expressed by the following expression,
where a and b are positive constants, and I is the external current. In the system (9), x stands for membrane potential, and y stands for spiking variable, [38]. To better express the complex dynamical behaviors of the neuron electrical activities, here a new 3-D memristive HR neuron model is proposed [39]. The external current I in the 2-D HR neuron model (8) be replaced by a memristor, the new HR neuron model can be described as,
Let the left-hand side of the system (10) be equal to zero, the equilibria can be solved by the following equation:
System (10) has a non-zero equilibrium point S = (0.58771263,
The characteristic equation is derived as:
where
The parameters in (10) are specified as follows: b = 5.5, c = 1.7, and d = 2.5, and the initial condition is (0, 0, 0). When a varies within the range of [2, 3.3], the bifurcation diagram of the membrane potential x and Lyapunov exponents are shown in Figures 8A,B. When the parameter a is increased in the region [2, 2.6], system (10) exhibits typical period-doubling bifurcation; when the range of parameter a varies in [2.6, 2.92], system (10) shows chaos; When parameter a is in the range of [2.92, 3.3], system (10) exhibits an inverse-period-doubling process. As shown in Figure 9, the neuronal electrical activity shows different modes by modifying the value of the system parameter a. Corresponding attractors are displayed in Figure 10.
FIGURE 8. Bifurcation and Lyapunov exponents of system (10) with b = 5.5, c = 1.7, d = 2.5 and initial condition (0, 0, 0) when parameter a varies in [2, 3.3]. (A) bifurcation, (B) Lyapunov exponents.
FIGURE 9. Time series of membrane potential under different parameters a of system (10) with b = 5.5, c = 1.7, d = 2.5 and initial condition (0, 0, 0): (A) a = 2.2, (B) a = 2.5, (C) a = 2.8, (D) a = 3.
FIGURE 10. Dynamics of system (10) with b = 5.5, c = 1.7, d = 2.5 and initial condition (0, 0, 0): (A) a = 2.2, (B) a = 2.5, (C) a = 2.8, (D) a = 3.
When a = 2.8, c = 1.7, and d = 2.5, and the initial condition is (0, 0, 0), the bifurcation diagram of the maxima X of the membrane potential x and Lyapunov exponents of parameter b varies in the range of [2, 13] are shown in Figures 11A,B. When parameter b is increased in the region of [0, 5.25], the system (10) exhibits typical period-doubling bifurcation phenomenon; When parameter b varies in [5.25, 5.77], [6.68, 7.59], [8.5, 8.63], [8.89, 9.28], [10.84, 10.97], and [12.27, 12.4], system (4) exhibits chaos; When parameter b is in the range of [5.77, 6.68], [7.59, 8.5], [8.63 8.89], [9.28, 10.84], and [10.97, 12.27], system (10) gives periodic solution. When b increases in the region of [12.27, 13], system (10) moves from chaos to period again. As shown in Figure 12, the bursting state of neuronal electrical activity can be changed into different modes by modifying the value of the system parameter b. As shown in Figure 13, attractors correspond to the different bursting states of neuronal electrical activity.
FIGURE 11. Bifurcation and Lyapunov exponents of system (10) with a = 2.8, c = 1.7, d = 2.5 and the initial conditions is (0, 0, 0) when the parameter b varies in [2, 13]. (A) bifurcation, (B) Lyapunov exponents.
FIGURE 12. Time series of membrane potential of system (10) with a = 2.8, c = 1.7, d = 2.5 and initial conditions (0, 0, 0): (A) b = 5.5, (B) b = 6.2, (C) b = 9.2, (D) b = 11.5.
FIGURE 13. Dynamics of system (10) with a = 2.8, c = 1.7, d = 2.5 and initial condition (0, 0, 0): (A) b = 5.5, (B) b = 6.2, (C) b = 9.2, (D) b = 11.5.
Also to observe the memristive computation influence on system dynamics, here the coefficient d is used as a bifurcation parameter in the derived HR neuron model. When a = 2.4, b = 5.5, c = 1.7, and the initial condition is (0, 0, 0), the bifurcation diagram of the maxima X of the membrane potential x and Lyapunov exponents of parameter d varies in the range of [1, 4] are shown in Figures 14A,B. When the parameter d is increased in the region of [0, 2.24], The system exhibits typical period-doubling bifurcation phenomenon; When the range of the parameter d vary in [2.24, 2.75], the system (10) is chaotic, obviously, there are two typical period windows in this chaotic range; When parameter d is in the range of [2.75, 4], system (10) exhibits an inverse-period-doubling process. Interestingly, the function of the parameter d is similar to the system parameter a.
FIGURE 14. Lyapunov exponents and bifurcation of system (10) with a = 2.8, b = 5.5, c = 1.7 and the initial conditions are (0, 0, 0) when the memristor parameter d varies in [1.8, 3.8]. (A) bifurcation, (B) Lyapunov exponents.
As shown in the latter, the newly introduced memristor does not break the property of offset boosting. Suppose there is a constant e introduced in both of the first dimension and the second dimension,
Different constants of e revise the offset of the system variable y directly. As shown in Figure 15, three chaotic attractors with different offsets are displayed in cyan, green, and red. Here signal x(t) at e = 0 is bipolar signal, while signals at x(t) at e =
FIGURE 15. Offset boosted attractors of system (11) with a = 2.8, b = 5.5, c = 1.7, d = 2.5: (A) attractors on plane of x-y, (B) signal y(t).
Conclusion
Memristor and memristive computation have great merits for producing chaos and dynamics control due to the special nonlinearity. It shows that even a memristor function is a linear function, the memory effect from memristive computation still returns chaos under a specific bifurcation. In this paper, two systems are reformed to be memristive chaotic systems based on the same memristor function. Offset boosting is discussed in both systems. Memristive computation as a new type of computing shows great potential with chaos-based engineering and pattern recognition in artificial intelligence, which deserves further research and will yield great value in information engineering.
Data Availability Statement
The original contributions presented in the study are included in the article/Supplementary Material, further inquiries can be directed to the corresponding author.
Author Contributions
All authors listed have made a substantial, direct, and intellectual contribution to the work and approved it for publication.
Funding
This work was supported financially by the National Natural Science Foundation of China (Grant no. 61871230), the Natural Science Foundation of Jiangsu Province (Grant no. BK20181410), and a Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions.
Conflict of Interest
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
Publisher’s Note
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Keywords: memristive computation, variable boostable chaotic system, hindmarsh-rose neuron model, offset boosting, dynamics control
Citation: Ma X, Li C, Wang R, Jiang Y and Lei T (2021) Memristive Computation-Oriented Chaos and Dynamics Control. Front. Phys. 9:759913. doi: 10.3389/fphy.2021.759913
Received: 17 August 2021; Accepted: 16 September 2021;
Published: 27 October 2021.
Edited by:
Christos Volos, Aristotle University of Thessaloniki, GreeceCopyright © 2021 Ma, Li, Wang, Jiang and Lei. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
*Correspondence: Chunbiao Li, Z29vbnRyeUAxMjYuY29t, Y2h1bmJpYW9sZWVAbnVpc3QuZWR1LmNu