Limit cycle problem for quadratic differential system x = -y + lx^2 + mxy, y =x(1 +ax +by)

The maximal number of limit cycles for a particular type Ⅲ system x = -y + lx2 + mxy, y =x(1 + ax + by) is studied and some errors that appeared in the paper by Suo Mingxia and Yue Xiting (Annals of Differential Equations, 2003,19(3):397-401) are corrected. By translating the system to be considered into the Lienard type and by using some related properties, we obtain several theorems with suitable conditions coefficients of the system, under which we prove that the system has at most two limit cycles. The conclusions improve the results given in Suo and Yue's paper mentioned above.

QUALITIVE THEORY OF THE QUADRATIC DIFFERENTIAL SYSTEMS (I)

Qualitative properties of critical points, integral lines and limit cycles are studied. Interesting relations between quantities characterizing local properties and those characterizing global properties are obtained.

Linear Quadratic Differential Game Strategies with Two-pursuit Versus Single-evader

In order to intercept the future targets that are characterized by high maneuverability, multiple interceptors may be launched and aimed at single target. The scenario of two missiles P and Q intercepting a single target is modeled as a two-pursuit single-evader non-zero-sum linear quadratic differential game. The intercept space is decomposed into three subspaces which are mutually disjoint and their union covers the entire intercept space. The effect of adding the second interceptor arises in the intercept space of both P and Q （PQ-intercept space）. A guidance law is derived from the Nash equilibrium strategy set （NESS） of the game. Simulation studies are focused on the PQ-intercept space. It is indicated that 1） increasing the target＇s maneuverability will enlarge PQ-intercept space; 2） the handover conditions will be released if the initial zero-effort-miss （ZEM） of both interceptors has opposite sign; 3） overvaluation of the target＇s maneuverability by choosing a small weight coefficient will generate robust performance with respect to the target maneuvering command switch time and decrease the fuel requirement; and 4） cooperation between interceptors increases the interception probability.

ON A CONJECTURE CONCERNING THE NON-EXISTENCE OF LIMIT CYCLES FOR QUADRATIC DIFFERENTIAL SYSTEMS

A conjecture on the non-existence of limit cycles for the quadratic differential system (1) under conditions (2) and iv) of (3) is discussed; interesting phenomena are revealed.

On the Conditions of a Center and General Integrals of Quadratic Differential Systems

We give the general integral of quadratic differential system with center in two cases under the Chinese classification.

LIMIT CYCLES AND BIFURCATION CURVES FOR THE QUADRATIC DIFFERENTIAL SYSTEM(III)_(m=0)HAVING THREE ANTI-SADDLES(II)

As a continuation of,the author studies the limit cycle bifurcation around the focus S_(1)other than O(0,0)for the system(1)asδvaries.A conjecture on the mon-existence of limit cycles around S_(1),and another one on the non-coexistence of limit cycles ariund both O and S_(1)are given,together with some numerical examples.

On the Limit Cycles of Quadratic Differential Systems

In this paper we give the necessary and sufficient conditions for all finite critical points of quadratic differential systems to be weak foci, and solve an open problem proposed by Yanqian Ye.

A Note on the Density of a Subset of All Integrable Holomorphic Quadratic Differentials

Let T0（Δ） be the subset of the universal Teichm¨uller space, which consists all of the elements with boundary dilatation 1. Let SQ（Δ） be the unit ball of the space Q（Δ） of all integrable holomorphic quadratic differentials on the unit disk Δ and Q0（Δ） be defined as Q0（Δ） = {？ ∈ SQ（Δ） ： there exists a k ∈（0, 1） such that [kˉ？ ｜？｜] ∈ T0（Δ）}. In this paper, we show that Q0（Δ） is dense in SQ（Δ）.

Solution of a zero-sum linear quadratic differential game with singular control cost of minimiser

We consider a finite horizon,zero-sum linear quadratic differential game.The feature of this game is that a weight matrix of the minimiser’s control cost in the cost functional is singular.Due to this singularity,the game can be solved neither by applying the Isaacs MinMax principle nor using the Bellman–Isaacs equation approach,i.e.this game is singular.Aprevious paper of one of the authors analysed such a game in the case where the cost functional does not contain the minimiser’s control cost at all,i.e.the weight matrix of this cost equals zero.In this case,all coordinates of the minimiser’s control are singular.In the present paper,we study the general case where the weight matrix of the minimiser’s control cost,being singular,is not,in general,zero.This means that only a part of the coordinates of the minimiser’s control is singular,while others are regular.The considered game is treated by a regularisation,i.e.by its approximate conversion to an auxiliary regular game.The latter has the same equation of dynamics and a similar cost functional augmented by an integral of the squares of the singular control coordinates with a small positive weight.Thus,the auxiliary game is a partial cheap control differential game.Based on a singular perturbation’s asymptotic analysis of this auxiliary game,the existence of the value of the original(singular)game is established,and its expression is obtained.The maximiser’s optimal state feedback strategy and the minimising control sequence in the original game are designed.It is shown that the coordinates of the minimising control sequence,corresponding to the regular coordinates of the minimiser’s control,are point-wise convergent in the class of regular functions.The optimal trajectory sequence and the optimal trajectory in the considered singular game also are obtained.An illustrative example is presented.

BIFURCATION DIAGRAMS OF QUADRATIC DIFFERENTIAL SYSTEMS HAVING ONE FOCUS AND ONE SADDLE

This paper gives bifurcation diagrams of system (2) below in the (α,λ) para meter plane.

PHASE-PORTRAIT OF A CERTAIN INTEGRABLE QUADRATIC DIFFERENTIAL SYSTEM WITH CENTER

We draw and analyse the phase-portrait of the integrable quadratic differential system (4) below, this result will be used in a latter paper.

A CLASS OF QUADRATIC DIFFERENTIAL SYSTEM WITH A THIRD ORDER WEAK FOCUS

This paper discusses the uniqueness of the limit cycle of quadratic differential system with a third order weak focus.

Pareto Efficiency of Finite Horizon Switched Linear Quadratic Differential Games

A switched linear quadratic（LQ） differential game over finite-horizon is investigated in this paper. The switching signal is regarded as a non-conventional player, afterwards the definition of Pareto efficiency is extended to dynamics switching situations to characterize the solutions of this multi-objective problem. Furthermore, the switched differential game is equivalently transformed into a family of parameterized single-objective optimal problems by introducing preference information and auxiliary variables. This transformation reduces the computing complexity such that the Pareto frontier of the switched LQ differential game can be constructed by dynamic programming. Finally, a numerical example is provided to illustrate the effectiveness.

ON NUMBER OF LIMIT CYCLES FOR THE QUADRATIC SYSTEMS WITH A WEAK FOCUS AND A STRONG FOCUS

It is proved that the quadratic system with a weak focus and a strong focus has at most one limit cycle around the strong focus, and as the weak focus is a 2nd order(or 3rd order) weak focus the quadratic system has at most two(one) limit cycles which have (1,1) distribution ((0,1) distribution).

QUALITATIVE THEORY OF THE QUADRATIC DIFFERENTIAL SYSTEMS (II)-ERGODICITY OF LIMIT CYCLES

In this paper we study the variation of limit cycles around different foci when a coefficient in the equation of the quadratic differential system varies.

THE VARIATION OF INVARIANT LINES AND LIMIT CYCLES FOR A QUADRATIC DIFFERENTIAL SYSTEM

In this paper we study the variation of invariant lines and limit cycles when acoefficient in a quadratic differential system varies.

ON THE INDEX-INVERSE PLANAR DIFFERENTIAL SYSTEM (I)

In this paper we study the relation of trajectories and limit cycles between index-inverse differential systems, especially, index-inverse quadratic differential systems.

THE PROOF OF THE NON-EXISTENCE OF LIMIT CYCLES FOR A QUADRATIC DIFFERETIAL SYSTEM

the authors give some results by using Dulac function method to prove the non-existence of limit cycles for a quadratic differetial system.

ON THE NON-EXISTENCE OF LIMIT CYCLES OF CERTAIN QUADRATIC SYSTEMS

In §1 and §3, two conjectures mentioned by Ye Yanqian are studied. In §2, by use of elementary methods the author proves some non-existence theorems of limit cycles (LC, for abbreviation) for quadratic differential systems obtained recently by H.Giacomini, J. Llibre and M. Viano.

Stable Teichmller mappings of type (0,4)

Let X = C\{0,1} and X = X\{}. We get a necessary and suficient condition on the position of in X such that X has stable Teichmller mappings. Furthermore, we can formulate all these stable Teichmller mappings. The main result in this paper partially answers a question posed by Kra.