On Chebyshev functions and Klee functions

Associated to a lower semicontinuous function, one can define its proximal mapping and farthest mapping. The function is called Chebyshev (Klee) if its proximal mapping (farthest mapping) is single-valued everywhere. We show that the function f is 1/λ-hypoconvex if its proximal mapping Pλf is single-valued. When the function f is bounded below, and Pλf is single-valued for every λ>0, the function must be convex. Similarly, we show that the function f is 1/μ-strongly convex if the farthest mapping Qμf is single-valued. When the function is the indicator function of a set, this recovers the well-known Chebyshev problem and Klee problem in Rn. We also give an example illustrating that a continuous proximal mapping (farthest mapping) needs not be locally Lipschitz, which answers one open question by Hare and Poliquin.     

On functions behaving like additive functions

Let 0 < 1. In the paper we consider the following inequality: |f(x + y) – f(x) – f(y)| min{|f(x + y)|, |f(x) + f(y)|}, wheref: R R. Solutions and continuous solutions of this inequality are investigated. They have similar properties as additive functions, e.g. if the solution is bounded above (below) on a set of positive inner Lebesgue measure then it is continuous. Some sufficient condition for this inequality is also given.Dedicated to Professor Otto Haupt with best wishes on his 100th birthday     

On quasi-orderings and multi-objective functions

In the paper the relationship between quasi-orderings (i.e. transitive and reflexive relations) and multi-objective functions (i.e. functions being a finite vector of continuous value functions) is investigated. A characterization of quasi-orderings representable by multi-objective functions is given.     

On pseudolinear functions

In this paper the structure of a smooth pseudolinear function is investigated and the general form of the gradient is given explicitly.     

On semidifferentiable functions

We prove that, under suitable assumptions, the two general schemes of generalized derivatives (K-derivatives, introduced in [3], and G-derivatives introduced in [4]) are equivalent. Afterwards we analyze some properties of the G-semidifferentiable functions which are important for treating extremum problems     

On Littlewood-Paley functions

We prove that, for a compactly supported function with vanishing integral on , the corresponding square function operator is bounded on for .

     

On spt-crank-type functions

In a recent paper, Andrews, Dixit, and Yee introduced a new spt-type function \({\mathrm {spt}}_{\omega }(n)\), which is closely related to Ramanujan’s third-order mock theta function \(\omega (q)\). Garvan and Jennings-Shaffer introduced a crank function which explains congruences for \({\mathrm {spt}}_{\omega }(n)\). In this article, we study the asymptotic behavior of this crank function and confirm a positivity conjecture of the crank asymptotically. We also study a sign pattern of the crank and congruences for \({\mathrm {spt}}_{\omega }(n)\).     

On progressive functions

Progressive functions at time t involve only the progressive functions at time before t and some nice compactly supported function at time t. We give sufficient conditions and explicit formulas to construct progressive functions with exponential decay and characterize the conditions on which the positive integer translates of a progressive function are orthonormal or a Riesz sequence. We provide explicit ways for construction of orthonormal progressive functions and for construction of the biorthogonal functions of nonorthogonal progressive functions. Such progressive functions can be used to construct wavelets with arbitrary smoothness on the half line if they are generated by a smooth refinable compactly supported function.