On the number of limit cycles of planar quadratic vector fields

Doklady Mathematics -     

On the number of limit cycles which appear by perturbation of two-saddle cycles of planar vector fields

We prove that the number of limit cycles which bifurcate from a two-saddle loop of an analytic planar vector field X ₀ under an arbitrary finite-parameter analytic deformation X _λ , λ ∈ (? ^N , 0), is uniformly bounded with respect to λ.     

On the number of limit cycles which appear by perturbation of Hamiltonian two-saddle cycles of planar vector fields

We find an upper bound to the maximal number of limit cycles, which bifurcate from a hamiltonian two-saddle loop of an analytic vector field, under an analytic deformation.     

On the number ofS-integral solutions toY m =f(X)

In this paper, we establish new upper bounds on the number ofS-integral solutions to hyper- and super-elliptic equations under the conditions ofLeVeque [3]. Our method is based upon that ofEvertse andSilverman [1].     

Upper bounds for the number of orbital topological types of planar polynomial vector fields modulo limit cycles

The purpose of this paper is to find an upper bound for the number of orbital topological types of nth-degree polynomial fields in the plane. An obstacle to obtaining such a bound is related to the unsolved second part of the Hilbert 16th problem. This obstacle is avoided by introducing the notion of equivalence modulo limit cycles. Earlier, the author obtained a lower bound of the form $2^{cn^2 } $ . In the present paper, an upper bound of the same form but with a different constant is found. Moreover, for each planar polynomial vector field with finitely many singular points, a marked planar graph is constructed that represents a complete orbital topological invariant of this field.     

Some criteria for the existence of limit cycles for quadratic vector fields

In this paper we consider real quadratic systems. We present new criteria for the existence and uniqueness of limit cycles for such systems by using Darbouxian particular solutions. Some results are based on the study of such systems in . We also generalize the well-know result of Bautin on the nonexistence of limit cycles for quadratic Lotka-Volterra systems.     

On the number of limit cycles of a monodromic polynomial vector field on the plane

Limit cycles of monodromic polynomial vector fields are studied. These are fields on the real plane with the unique singular point 0 whose components are polynomials and whose phase portraits are diffeomorphic to a linear focus. The number of limit cycles of such a field is estimated from above in terms of the degrees of the polynomials, the maximum of the absolute values of their coefficients, and certain characteristics of the monodromy transformation, which can be called multipliers at zero and infinity. The estimate is based on the growth and zeros theorem for holomorphic functions.     

Some Remarks on the Number of Solutions to the Equation f(X1) + … + f(Xn) = 0

Let S, T be finite sets, and let f be a function from S to T. Fix an element t in T, and let c_n denote the number of n-tuples (X₁,…,X_n) satisfying f(X₁) + … + f(X_n) = t here + denotes any binary operation on T. The sequence c₁, c₂,… satisfies a linear recurrence relation of degree at most |T|.     

Bifurcation set and number of limit cycles in Z2-equivariant planar vector fields of degree 5

An Z₂-equivariant polynomial Hamiltonian system of degree 5 with two perturbation terms is considered in this paper. The phase plane (a, b) is divided into 15 different regions which give the bifurcation set of the system. Using the bifurcation theory of planar dynamical system and the method of detection function, we obtain the bifurcation set and the configurations of compound eyes of the system with 21 or 23 limit cycles.     

On the system of functional equationsf(x + y) = f(x) + f(y) andf(xy) = p (x)f(y) + q(y)f(x)

Aequationes mathematicae -     

Bifurcation of limit cycles for the quadratic differential system (III)l=n=0

In this paper we will prove that limit cycles for the quadratic differential system (III)l=n=0 in Chinese classification are concentratedly distributed, and that the maximum number of limit cycles around O (0,0) is at least two. This project is supported by the Natural Science Foundation of Educational Committee of Jiangsu Province.     

On the construction of bifurcation curves related to limit cycles of multiplicity three for planar vector fields

We consider planar vector fields f(x,y,λ)$f(x,y,\lambda )$ depending on a three-dimensional parameter vector λ$\lambda$. We assume f(0,0,λ)≡0$f(0,0,\lambda )\equiv 0$ and that there exists a parameter value λ=_λ0$\lambda ={\lambda }_0$ connected with the Andronov–Hopf bifurcation of a limit cycle of multiplicity three from the origin. We describe an algorithm to continue the corresponding local Andronov–Hopf bifurcation curve in the parameter space which is based on the continuation of a periodic orbit to some augmented vector field and the construction of a Poincaré function to another augmented system.     

On the number of limit cycles of some systems on the cylinder

In this article we give two criteria for bounding the number of non-contractible limit cycles of a family of differential systems on the cylinder. This family includes Abel equations as well as the polar expression of several types of planar polynomial systems given by the sum of three homogeneous vector fields.