Zeros and fixed points of difference operators of meromorphic functions

Let f be a transcendental meromorphic function and Δf(z) = f(z + 1) − f(z). A number of results are proved concerning the existences of zeros and fixed points of Δ f(z) and Δ f(z)/f(z) when f(z) is of order σ(f)=1. Examples show that some of the results are sharp.     

Graph maps whose periodic points form a closed set

A continuous map f from a graph G to itself is called a graph map. Denote by P(f), R(f), ω(f), Ω(f) and CR(f) the sets of periodic points, recurrent points, ω-limit points, non-wandering points and chain recurrent points of f respectively. It is well known that P(f)⊂R(f)⊂ω(f)⊂Ω(f)⊂CR(f). Block and Franke (1983) [5] proved that if f:I→I is an interval map and P(f) is a closed set, then CR(f)=P(f). In this paper we show that if f:G→G is a graph map and P(f) is a closed set, then ω(f)=R(f). We also give an example to show that, for general graph maps f with P(f) being a closed set, the conclusion ω(f)=R(f) cannot be strengthened to Ω(f)=R(f) or ω(f)=P(f).     

Linear transformations of monotone functions on the discrete cube

For a function f:{0,1}ⁿ→R and an invertible linear transformation L∈GL_n(2), we consider the function Lf:{0,1}ⁿ→R defined by Lf(x)=f(Lx). We raise two conjectures: First, we conjecture that if f is Boolean and monotone then I(Lf)≥I(f), where I(f) is the total influence of f. Second, we conjecture that if both f and L(f) are monotone, then f=L(f) (up to a permutation of the coordinates). We prove the second conjecture in the case where L is upper triangular.     

Fourier expansion of Arakawa lifting I: An explicit formula and examples of non-vanishing lifts

Given an elliptic cusp form f and an automorphic form f?? on a definite quaternion algebra over ?, there is a theta lifting from (f, f??) to an automorphic form ?(f, f??) on the quaternion unitary group GSp(1, 1) generating quaternionic discrete series at the Archimedean place. The aim of this paper is to provide an explicit formula for Fourier coefficients of ?(f, f??) in terms of periods of f and f?? with respect to a unitary character ?? of an imaginary quadratic field. As an application, we show the existence of (f, f??) with ?(f, f??) ? 0.     

Implications of pseudo-orbit tracing property for continuous maps on compacta

We look at the dynamics of continuous self-maps of compact metric spaces possessing the pseudo-orbit tracing property (i.e., the shadowing property). Among other things we prove the following: (i) the set of minimal points is dense in the non-wandering set Ω(f), (ii) if f has either a non-minimal recurrent point or a sensitive minimal subsystem, then f has positive topological entropy, (iii) if X is infinite and f is transitive, then f is either an odometer or a syndetically sensitive non-minimal map with positive topological entropy, (iv) if f has zero topological entropy, then Ω(f) is totally disconnected and f restricted to Ω(f) is an equicontinuous homeomorphism.     

Boundedness and compactness of Hankel operators on the sphere

We consider Hankel operators on the Hardy space of the unit sphere in Cn. We show that a large amount of information about the function f−Pf can be recovered from the Hankel operator Hf. For example, if Hf is compact, then the function f−Pf is necessarily in VMO.     

The extended f-vectors of 4-polytopes

For P a d-dimensional convex polytope and S = {i₁,…, i_s} ⊂ {0, 1,…, d−1}, let f_s(P) be the number of chains of faces Ø ⊂ F₁ ⊂ F₂ ⊂ … ⊂ F_s ⊂ P with dim F_j = i_j. By the generalized Dehn-Sommerville equations the dimension of the affine span of the extended f-vectors (f_s(P))_S ⊂ {0,1,2,3} as P ranges over all 4-polytopes is 4, and the extended f-vectors are determined by the values of f₀, f₁, f₂ and f₀₂. Six linear and four nonlinear inequalities on extended f-vectors of 4-polytopes are given. The consequences for the basic f-vector, (f₀, f₁, f₂, f₃), are derived. These include the inequality, 4f₂ ⩾ 3f₀ − 10 + 7f₃, conjectured by Barnette.     

The stability of a cubic type functional equation with the fixed point alternative

In this note we investigate the generalized Hyers-Ulam-Rassias stability for the new cubic type functional equation f(x+y+2z)+f(x+y−2z)+f(2x)+f(2y)=2[f(x+y)+2f(x+z)+2f(x−z)+2f(y+z)+2f(y−z)] by using the fixed point alternative. The first systematic study of fixed point theorems in nonlinear analysis is due to G. Isac and Th.M. Rassias [Internat. J. Math. Math. Sci. 19 (1996) 219-228].     

On the packing dimension of the Julia set and the escaping set of an entire function

Let f be a transcendental entire function. We give conditions which imply that the Julia set and the escaping set of f have packing dimension 2. For example, this holds if there exists a positive constant c less than 1 such that the minimum modulus L(r, f) and the maximum modulus M(r, f) satisfy log L(r, f) ≤ c logM(r, f) for large r. The conditions are also satisfied if logM(2r, f) ≥ d logM(r, f) for some constant d greater than 1 and all large r.     

On the representation of functions as a sum of derivatives

We show that there is an integrable function g of two variables which cannot be represented as a sum g = f₀ + ∂f₁ + ∂₂f₂, where f₀,f₁,f₂ are functions with integrable gradient.     

Mappings of Finite Distortion of Polynomial Type

Suppose f:? ⁿ →? ⁿ is a mapping of K-bounded p-mean distortion for some p>n?1. We prove the equivalence of the following properties of f: the doubling condition for J(x,f) over big balls centered at the origin, the boundedness of the multiplicity function N(f,? ⁿ ), the polynomial type of f, and the polynomial growth condition for f.     

On constructing new expansions of functions using linear operators

Let T,U be two linear operators mapped onto the function f such that U(T(f))=f, but T(U(f))≠f. In this paper, we first obtain the expansion of functions T(U(f)) and U(T(f)) in a general case. Then, we introduce four special examples of the derived expansions. First example is a combination of the Fourier trigonometric expansion with the Taylor expansion and the second example is a mixed combination of orthogonal polynomial expansions with respect to the defined linear operators T and U. In the third example, we apply the basic expansion U(T(f))=f(x) to explicitly compute some inverse integral transforms, particularly the inverse Laplace transform. And in the last example, a mixed combination of Taylor expansions is presented. A separate section is also allocated to discuss the convergence of the basic expansions T(U(f)) and U(T(f)).     

Invariant subspaces of some function spaces on a locally compact group

Let G be a σ-compact and locally compact group. If f?L^∞(G) let U_f be the closed subspace of L^∞(G) generated by the left translations of f. Conditions are given which ensure that each function in U_f may be expanded in an essentially unique way as an absolutely convergent series of translations of f. In this case U_f contains subspaces which are isometrically isomorphic to l¹. If G is metrizable and nondiscrete there is a continuum Γ in L^∞(G) such that, for each f?Γ, U_f contains no non-zero continuous function, and for f, g?Γ with f ≠ g, U_f ∩ U_g = {0}. If G is non-compact, metrizable, and non-discrete there is a continuum Γ of bounded continuous functions on G such that, for each f?Γ, U_f contains no non-zero left uniformly continuous function, and for f, g?Γ with f ≠ g, U_f ∩ U_g = {0}. The subspaces U_f above are translation invariant but are not convolution invariant.     

On strong ergodicity and chaoticity of systems with the asymptotic average shadowing property

Let X be a compact metric space and f: X → X be a continuous map. In this paper, we investigate the relationships between the asymptotic average shadowing property (Abbrev. AASP) and other notions known from topological dynamics. We prove that if f has the AASP and the minimal points of f are dense in X, then for any n ? 1, f × f × ? × f(n times) is totally strongly ergodic. As a corollary, it is shown that if f is surjective and equicontinuous, then f does not have the AASP. Moreover we prove that if f is point distal, then f does not have the AASP. For f: [0, 1] → [0, 1] being surjective continuous, it is obtained that if f has two periodic points and the AASP, then f is Li-Yorke chaotic.     

On a new notion of the solution to an ill-posed problem

A new understanding of the notion of the stable solution to ill-posed problems is proposed. The new notion is more realistic than the old one and better fits the practical computational needs. A method for constructing stable solutions in the new sense is proposed and justified. The basic point is: in the traditional definition of the stable solution to an ill-posed problem Au=f, where A is a linear or nonlinear operator in a Hilbert space H, it is assumed that the noisy data {f_δ,δ} are given, ‖f−f_δ‖≤δ, and a stable solution u_δ:=R_δf_δ is defined by the relation lim_δ→0‖R_δf_δ−y‖=0, where y solves the equation Au=f, i.e., Ay=f. In this definition y and f are unknown. Any f∈B(f_δ,δ) can be the exact data, where B(f_δ,δ):={f:‖f−f_δ‖≤δ}.The new notion of the stable solution excludes the unknown y and f from the definition of the solution. The solution is defined only in terms of the noisy data, noise level, and an a priori information about a compactum to which the solution belongs.     

Stability of a functional equation deriving from cubic and quadratic functions

In this paper we establish the general solution of the functional equation 6f(x+y)−6f(x−y)+4f(3y)=3f(x+2y)−3f(x−2y)+9f(2y) and investigate the Hyers-Ulam-Rassias stability of this equation.     

The least common multiple of a sequence of products of linear polynomials

Let f(x) be the product of several linear polynomials with integer coefficients. In this paper, we obtain the estimate log?lcm?(f(1),…,f(n))～An as n→∞, where A is a constant depending on?f.     

The classification of complete graphsK n onf-coloring

Anf-coloring of a graphG=(V, E) is a coloring of edge setE such that each color appears at each vertexv ∈ V at mostf(v) times. The minimum number of colors needed tof-colorG is called thef-chromatic index χ′ _f (G) ofG. Any graphG hasf-chromatic index equal to Δ _f (G) or Δ _f (G) + 1 where $\Delta _f (G) = \mathop {\max }\limits_{v \in V} \left\{ {\left\lceil {\frac{{d(v)}}{{f(v)}}} \right\rceil } \right\}$ . If χ′ _f (G) = Δ _f (G), thenG is ofC _f 1; otherwiseG is ofC _f 2. In this paper, the classification problem of complete graphs onf-coloring is solved completely.     

On the stability of a quartic functional equation

In this paper, we prove the generalized Hyers-Ulam stability for the following quartic functional equation

f(2x+y)+f(2x−y)=4f(x+y)+4f(x−y)+24f(x)−6f(y).     

Value distribution and shared sets of differences of meromorphic functions

We investigate value distribution and uniqueness problems of difference polynomials of meromorphic functions. In particular, we show that for a finite order transcendental meromorphic function f with λ(1/f)<ρ(f) and a non-zero complex constant c, if n?2, then fn(z)f(z+c) assumes every non-zero value a∈C infinitely often. This research also shows that there exist two sets S₁ with 9 (resp. 5) elements and S₂ with 1 element, such that for a finite order nonconstant meromorphic (resp. entire) function f and a non-zero complex constant c, Ef(z)(Sj)=Ef(z+c)(Sj)(j=1,2) imply f(z)≡f(z+c). This gives an answer to a question of Gross concerning a finite order meromorphic function f and its shift.