On the existence and uniqueness of limit cycles in planar continuous piecewise linear systems without symmetry

https://doi.org/10.1016/j.nonrwa.2013.02.004Get rights and content

Highlights

  • Non-symmetric planar continuous piecewise-linear differential systems are studied.

  • Some results about the existence and uniqueness of their limit cycles are given.

  • For systems with three linear zones and no symmetries new results are obtained.

  • For systems with two linear zones a shorter proof of known results is achieved.

  • The application to the McKean model of a single neuron activity is described.

Abstract

Some techniques to show the existence and uniqueness of limit cycles, typically stated for smooth vector fields, are extended to continuous piecewise-linear differential systems.

New results are obtained for systems with three linearity zones without symmetry and having one equilibrium point in the central region. We also revisit the case of systems with only two linear zones giving shorter proofs of known results.

A relevant application to the McKean piecewise linear model of a single neuron activity is included.

Section snippets

Introduction and statement of main results

For planar differential systems, the analysis of the possible existence of limit cycles and their uniqueness is a problem which has attracted the interest of many works in the past. For smooth systems, good classical references in the field are the books [1], [2]. The restriction of this problem to polynomial differential equations is the well-known 16th Hilbert’s problem [3]. Since Hilbert’s problem turns out to be a strongly difficult one, Smale [4] has particularized it to Liénard

Applications

We analyze here a celebrated continuous piecewise linear model in mathematical biology. Following [20], the equations for the two-dimensional McKean model of a single neuron activity take the form Cv̇=f(v)w+I,ẇ=vγw, where v stands for the voltage, w is the gating variable and f(v)={vif v<a/2,vaif a/2v(1+a)/2,1vif v>(1+a)/2. Here, C>0,γ>0,I is a constant drive, and f(v) is a CPWL caricature of the cubic FitzHugh–Nagumo nonlinearity f(v)=v(1v)(va), provided that 0<a<1, see [20] for more

The Massera’s method for uniqueness of limit cycles

We review in this section a geometrical argument which is usually known as Massera’s method; it will allow us, after adequate adaptations, to show the uniqueness of limit cycles in the CPWL differential systems considered in this paper, when they satisfy certain hypotheses. Uniqueness results for limit cycles are typically rather involved; see [1], [2], for a review on the subject. Here we reformulate in a specific way the simple and elegant idea proposed by J.L. Massera in his brief note

Preliminary results and uniqueness of limit cycles

In this section we give some preliminary results and also include uniqueness results for possible periodic orbits. Note that if we make in system (1) the change X=x,Y=y we get the system Ẋ=F˜(X)Y,Ẏ=g˜(X)+δ, where the new functions F˜ and g˜ are obtained from that given in (2) by interchanging the subscripts L and R. Thus, there is no loss of generality in assuming δ0 hereafter.

Our first result is just a preparation lemma, reducing by one the number of parameters and looking for a more

Existence of limit cycles and proof of main results

In this section we will use as main tools the Poincaré return map to show the existence of periodic orbits. We start by considering systems with three linearity zones given in (12), (13), (14) with xL<0<xR for which the conditions aL,aR<0,aC>0 and bL,bR0 hold. We will use the positive and negative parts of the y-axis as domain and range for defining two different half-return maps, namely a right half-return map PR and a left half-return map PL.

We start by studying the qualitative properties of

Acknowledgments

J. Llibre is partially supported by a MICINN/FEDER grant number MTM2008-03437, by an AGAUR grant number 2009SGR-410 and by ICREA Academia. M. Ordóñez is partially supported by a MICINN/FEDER grant number ECO2010-17766. E. Ponce is partially supported by a MICINN/FEDER grant number MTM2009-07849 and Junta de Andalucía grant number P08-FQM-03770; he also wants to acknowledge Prof. Marco Sabatini for his helpful suggestions and discussions on Massera’s method.

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