On generalized Ekeland’s variational principle and equivalent formulations for set-valued mappings

We propose a very weak type of generalized distances called a weak τ-function and use it to weaken the assumptions about lower semicontinuity in existing versions of Ekeland’s variational principle and equivalent formulations.     

Newton’s method on generalized Banach spaces

We present a weaker convergence analysis of Newton’s method than in Kantorovich and Akilov (1964), Meyer (1987), Potra and Ptak (1984), Rheinboldt (1978), Traub (1964) on a generalized Banach space setting to approximate a locally unique zero of an operator. This way we extend the applicability of Newton’s method. Moreover, we obtain under the same conditions in the semilocal case weaker sufficient convergence criteria; tighter error bounds on the distances involved and an at least as precise information on the location of the solution. In the local case we obtain a larger radius of convergence and higher error estimates on the distances involved. Numerical examples illustrate the theoretical results.     

A short proof of Botha’s theorem on products of idempotent linear mappings

We give an elementary self-contained proof to Botha’s theorem on the factorization of a singular transformation into idempotent mappings.     

A link between Wilson’s and d’Alembert’s functional equations

If \({f, g : G \to \mathbb{C}}\), f ≠ 0, is a solution of Wilson’s functional equation on a group G, then g is a d’Alembert function.     

Jensen’s inequality and new entropy bounds

We establish new lower and upper bounds for Jensen’s discrete inequality. Applying those results in information theory, we obtain new and more precise bounds for Shannon’s entropy.     

Sard’s theorem for mappings between Fréchet manifolds

We prove an infinite-dimensional version of Sard’s theorem for Fréchet manifolds. Let M (respectively, N) be a bounded Fréchet manifold with compatible metric d _M (respectively, d _N ) modeled on Fréchet spaces E (respectively, F) with standard metrics. Let f : M → N be an MC ^k -Lipschitz–Fredholm map with k > max{Ind f, 0}: Then the set of regular values of f is residual in N.     

A note on Jensen’s inequality for BSDEs

Under the Lipschitz assumption and square integrable assumption on g, Jiang proved that Jensen＇s inequality for BSDEs with generator g holds in general if and only if g is independent of y, g is super homogenous in z and g（t, 0） = 0, a.s., a.e.. In this paper, based on Jiang＇s results, under the same assumptions as Jiang＇s, we investigate the necessary and sufficient condition on g under which Jensen＇s inequality for BSDEs with generator g holds for some specific convex functions, which generalizes some known results on Jensen＇s inequality for BSDEs.     

Existence and approximation of fixed points of multivalued generalized α-nonexpansive mappings in Banach spaces

Numerical Algorithms - We consider the theoretical and numerical aspects of the quadrature rules associated with a sequence of polynomials generated by a special RII recurrence relation. We also...     

Rubio cubics and generalized Cundy–Parry mappings

Rubio’s mappings between the Thomson and Darboux cubics are generalized for pairs of cubics of the form p α(β ²?γ ²)+ q β(γ ²?α ²)+ r γ(α ² ? β ²) = 0, where p, r, q, α, β, γ are functions of a triple (a, b, c) of variables or indeterminates. Methods include symbolic substitutions, such as (a, b, c) → (bc, ca, ab). Connections between the generalized Rubio mappings with generalized Cundy–Parry mappings are described.     

A structural connection between linear and 0–1 integer linear formulations

The connection between linear and 0–1 integer linear formulations has attracted the attention of many researchers. The main reason triggering this interest has been an availability of efficient computer programs for solving pure linear problems including the transportation problem. Also the optimality of linear problems is easily verifiable through existing algorithms. However, there is no efficient general technique available to solve 0–1 integer linear problems or to verify their optimality. This paper shows that in the case of one of the easier 0–1 integer linear problems, namely a single assignment problem, such a relation between linear and 0–1 integer linear formulation can be built. The theory behind the proposed ‘bridge’ is based on the combination of the absolute point principle and shadow price theory. The main practical benefit of this work is in providing an algorithm to find a MFL (more-for-less) solution for the assignment problem. To the best of our knowledge, this is one of the first efforts to provide a ‘more-for-less’ result for a 0–1 integer linear problem.     

On Jensen’s inequality and Hölder’s inequality for g-expectation

In this paper, we shall prove that for n > 1, the n-dimensional Jensen inequality holds for the g-expectation if and only if g is independent of y and linear with respect to z, in other words, the corresponding g-expectation must be linear. A Similar result also holds for the general nonlinear expectation defined in Coquet et al. (Prob. Theory Relat. Fields 123 (2002), 1–27 or Peng (Stochastic Methods in Finance Lectures, LNM 1856, 143–217, Springer-Verlag, Berlin, 2004). As an application of a special n-dimensional Jensen inequality for g-expectation, we give a sufficient condition for g under which the Hölder’s inequality and Minkowski’s inequality for the corresponding g-expectation hold true.     

Lipschitz selections of set-valued mappings and Helly’s theorem

We prove a Helly-type theorem for the family of all m-dimensional convex compact subsets of a Banach space X. The result is formulated in terms of Lipschitz selections of set-valued mappings from a metric space (M, ρ) into this family. Let M be finite and let F be such a mapping satisfying the following condition: for every subset M′ ⊂ M consisting of at most 2^m+1 points, the restriction F|_M′ of F to M′ has a selection f_M′ (i. e., f_M′(x) ∈ F(x) for all x ∈ M′) satisfying the Lipschitz condition ‖ƒ_M′(x) − ƒ_M′(y)‖_X ≤ ρ(x, y), x, y ∈ M′. Then F has a Lipschitz selection ƒ: M → X such that ‖ƒ(x) − ƒ(y)‖_X ≤ γρ(x,y), x, y ∈ M where γ is a constant depending only on m and the cardinality of M. We prove that in general, the upper bound of the number of points in M′, 2^m+1, is sharp. If dim X = 2, then the result is true for arbitrary (not necessarily finite) metric space. We apply this result to Whitney’s extension problem for spaces of smooth functions. In particular, we obtain a constructive necessary and sufficient condition for a function defined on a closed subset of R ² to be the restriction of a function from the Sobolev space W _∞ ² (R ²).A similar result is proved for the space of functions on R ² satisfying the Zygmund condition.     

Deligne’s congruence and supersingular reduction of Drinfeld modules

Most rank two Drinfeld modules are known to have infinitely many supersingular primes. But how many supersingular primes of a given degree can a fixed Drinfeld module have? In this paper, a congruence between the Hasse invariant and a certain Eisenstein series is used for obtaining a bound on the number of such supersingular primes. Certain exceptional cases correspond to zeros of certain Eisenstein series with rational j-invariants.     

Pillai’s generalized function

The distribution of values of Pillai’s function over the ring of Gauss integers $ \mathbb{Z}\left[ i \right] $ is studied. The asymptotic formulas for the summators $ {\varSigma_{{N\left( \alpha \right)\leq x}}}\frac{{g\left( \alpha \right)}}{{{N^{\alpha }}\left( \alpha \right)}} $ , where $ a\in \mathbb{R} $ , are found.     

Ramanujan’s cubic transformation and generalized modular equation

We study the quotient of hypergeometric functionsμ_a~*(r)=π/2sin(πa) F(a,1-a;1;1-r~3)/F(a,1-a;1;r~3),r∈(0,1)in the theory of Ramanujan's generalized modular equation for a ∈(0,1/2],and find an infinite product formula for μ_(1/3)~*(r) by use of the properties of μ_a~*(r) and Ramanujan's cubic transformation.Besides,a new cubic transformation formula of hypergeometric function is given,which complements the Ramanujan's cubic transformation.     

A sharp lower bound of Burkholder’s functional for K-quasiconformal mappings and its applications

In this paper, for \(K\) -quasiconformal mappings of a bounded domain into the complex plane, we build a sharp lower bound of Burkholder’s functional. As an application, we give two explicit and sharp lower bounds of Burkholder’s integrals for two subclasses of \(K\) -quasiconformal mappings, respectively. As the second application, we obtain a sharp upper bound of the \(L^p\) -integral of \(\sqrt{J_f}\) for certain \(K\) -quasiconformal mappings.