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 Aequationes Mathematicae   [SJR: 0.882]   [H-I: 23]   [2 followers]  Follow         Hybrid journal (It can contain Open Access articles)    ISSN (Print) 1420-8903 - ISSN (Online) 0001-9054    Published by Springer-Verlag  [2352 journals]
• Binary partitions and binary partition polytopes
• Authors: George E. Andrews; Jim Lawrence
Pages: 859 - 869
Abstract: This paper delves into the number of partitions of positive integers n into powers of 2 in which exactly m powers of 2 are used an odd number of times. The study of these numbers is motivated by their connections with the f-vectors of the binary partition polytopes.
PubDate: 2017-10-01
DOI: 10.1007/s00010-017-0493-8
Issue No: Vol. 91, No. 5 (2017)

• On Hermite–Hadamard inequality for $${\varvec{h}}$$ h -convex stochastic
processes
• Authors: Libo Li; Zhiwei Hao
Pages: 909 - 920
Abstract: In this paper, we investigate the Hermite–Hadamard type inequality for the class of some h-convex stochastic processes, which is an extension of the Hermite–Hadamard inequality given by Barráez et al. (Math. Æterna 5:571–581, 2015). We also provide the estimates of both sides of the Hermite–Hadamard type inequality for h-convex stochastic processes, where h is any non-negative function with $$h(t)+h(1-t)\le 1$$ for $$0\le t\le 1$$ .
PubDate: 2017-10-01
DOI: 10.1007/s00010-017-0488-5
Issue No: Vol. 91, No. 5 (2017)

• On certain generalizations of the Levi-Civita and Wilson functional
equations
• Authors: J. M. Almira; E. V. Shulman
Pages: 921 - 931
Abstract: We study the functional equation \begin{aligned} \sum _{i=1}^mf_i(b_ix+c_iy)= \sum _{k=1}^nu_k(y)v_k(x) \end{aligned} with $$x,y\in \mathbb {R}^d$$ and $$b_i,c_i\in {GL}(d,\mathbb {R})$$ , both in the classical context of continuous complex-valued functions and in the framework of complex-valued Schwartz distributions, where these equations are properly introduced in two different ways. The solution sets are, typically, exponential polynomials and, in some particular cases, related to the so called characterization problem of the normal distribution in Probability Theory, they reduce to ordinary polynomials.
PubDate: 2017-10-01
DOI: 10.1007/s00010-017-0489-4
Issue No: Vol. 91, No. 5 (2017)

• On $$\varvec{n}$$ n -norm preservers and the Aleksandrov conservative
$$\varvec{n}$$ n -distance problem
• Authors: György Pál Gehér
Pages: 933 - 943
Abstract: The goal of this paper is to point out that the results obtained in the recent papers (Chen and Song in Nonlinear Anal 72:1895–1901, 2010; Chu in J Math Anal Appl 327:1041–1045, 2007; Chu et al. in Nonlinear Anal 59:1001–1011, 2004a, J. Math Anal Appl 289:666–672, 2004b) can be seriously strengthened in the sense that we can significantly relax the assumptions of the main results so that we still get the same conclusions. In order to do this first, we prove that for $$n \ge 3$$ any transformation which preserves the n-norm of any n vectors is automatically plus-minus linear. This will give a re-proof of the well-known Mazur–Ulam-type result that every n-isometry is automatically affine ( $$n \ge 2$$ ) which was proven in several papers, e.g. in Chu et al. (Nonlinear Anal 70:1068–1074, 2009). Second, following the work of Rassias and Šemrl (Proc Am Math Soc 118:919–925, 1993), we provide the solution of a natural Aleksandrov-type problem in n-normed spaces, namely, we show that every surjective transformation which preserves the unit n-distance in both directions ( $$n\ge 2$$ ) is automatically an n-isometry.
PubDate: 2017-10-01
DOI: 10.1007/s00010-017-0478-7
Issue No: Vol. 91, No. 5 (2017)

• A note on Wilson’s functional equation
• Authors: Henrik Stetkær
Pages: 945 - 947
Abstract: Let S be a semigroup, and $$\mathbb {F}$$ a field of characteristic $$\ne 2$$ . If the pair $$f,g:S \rightarrow \mathbb {F}$$ is a solution of Wilson’s $$\mu$$ -functional equation such that $$f \ne 0$$ , then g satisfies d’Alembert’s $$\mu$$ -functional equation.
PubDate: 2017-10-01
DOI: 10.1007/s00010-017-0481-z
Issue No: Vol. 91, No. 5 (2017)

• Characterization theorems for Q -independent random variables with values
in a locally compact Abelian group
Pages: 949 - 967
Abstract: Let X be a locally compact Abelian group, Y be its character group. Following A. Kagan and G. Székely we introduce a notion of Q-independence for random variables with values in X. We prove group analogues of the Cramér, Kac–Bernstein, Skitovich–Darmois and Heyde theorems for Q-independent random variables with values in X. The proofs of these theorems are reduced to solving some functional equations on the group Y.
PubDate: 2017-10-01
DOI: 10.1007/s00010-017-0479-6
Issue No: Vol. 91, No. 5 (2017)

• Orthogonalities, linear operators, and characterization of inner product
spaces
• Authors: Senlin Wu; Chan He; Guang Yang
Pages: 969 - 978
Abstract: It is proved that a normed space, whose dimension is at least three, admitting a nonzero linear operator reversing Birkhoff orthogonality is an inner product space, which releases the smoothness condition in one of J. Chmieliński’s results. Further characterizations of inner product spaces are obtained by studying properties of linear operators related to Birkhoff orthogonality and isosceles orthogonality.
PubDate: 2017-10-01
DOI: 10.1007/s00010-017-0494-7
Issue No: Vol. 91, No. 5 (2017)

• Weighted entropy and optimal portfolios for risk-averse Kelly investments
• Authors: M. Kelbert; I. Stuhl; Y. Suhov
Abstract: Following a series of works on capital growth investment, we analyse log-optimal portfolios where the return evaluation includes ‘weights’ of different outcomes. The results are twofold: (A) under certain conditions, the logarithmic growth rate leads to a supermartingale, and (B) the optimal (martingale) investment strategy is a proportional betting. We focus on properties of the optimal portfolios and discuss a number of simple examples extending the well-known Kelly betting scheme. An important restriction is that the investment does not exceed the current capital value and allows the trader to cover the worst possible losses. The paper deals with a class of discrete-time models. A continuous-time extension is a topic of an ongoing study.
PubDate: 2017-11-11
DOI: 10.1007/s00010-017-0515-6

• Authors: Bruce Ebanks
Abstract: In 1990, Benz asked whether a real additive mapping satisfying $$xf(y)=yf(x)$$ for all points (x, y) on the unit circle must be linear. In 2005, Boros and Erdei showed that it must be so. Here we generalize the problem to a pair of additive functions f, g related by the functional equation $$xf(y)=yg(x)$$ for all points (x, y) on a specified curve. We find that for many (but not all) types of curves this forces f and g to be equal and linear.
PubDate: 2017-10-23
DOI: 10.1007/s00010-017-0514-7

• Beta-type functions and the harmonic mean
• Authors: Martin Himmel; Janusz Matkowski
Abstract: For arbitrary $$f:\left( a,\infty \right) \rightarrow \left( 0,\infty \right) ,$$ $$a\ge 0,$$ the bivariable function $$B_{f}:\left( a,\infty \right) ^{2}\rightarrow \left( 0,\infty \right) ,$$ related to the Euler Beta function, is considered. It is proved that $$B_{f\text { }}$$ is a mean iff it is the harmonic mean H. Some applications to the theory of iterative functional equations are given.
PubDate: 2017-10-23
DOI: 10.1007/s00010-017-0498-3

• Families of conditionally approximately convex functions
• Authors: Marek Żołdak
Abstract: Let $$(G,+)$$ be an Abelian topological group, which is also a $$T_{0}$$ -space and a Baire space simultaneously, D be an open connected subset of G and $$\alpha : D-D \rightarrow {\mathbb R}$$ be a function continuous at zero and such that $$\alpha (0)=0$$ . We show that if $$(f_n)$$ is a sequence of continuous functions $$f_n : D \rightarrow {\mathbb R}$$ such that $$f_n(z) \le \frac{1}{2} f_n(x)+\frac{1}{2}f(y)+\alpha (x-y)$$ for $$n\in {\mathbb N}$$ and $$x,y,z\in D$$ such that $$2z=x+y$$ and if $$(f_n)$$ is pointwise convergent [bounded] then it is convergent uniformly on compact subsets of D [in the case when G is additionally a separable space, it contains a subsequence which is convergent on compact subsets of D].
PubDate: 2017-10-19
DOI: 10.1007/s00010-017-0511-x

• The Cosine–Sine functional equation on a semigroup with an
involutive automorphism
• Authors: Omar Ajebbar; Elhoucien Elqorachi
Abstract: We determine the complex-valued solutions of the following extension of the Cosine–Sine functional equation \begin{aligned} f(x\sigma (y))=f(x)g(y)+g(x)f(y)+h(x)h(y),\quad x,y\in S, \end{aligned} where S is a semigroup generated by its squares and $$\sigma$$ is an involutive automorphism of S. We express the solutions in terms of multiplicative and additive functions.
PubDate: 2017-10-12
DOI: 10.1007/s00010-017-0512-9

• Lower estimation of the difference between quasi-arithmetic means
• Authors: Paweł Pasteczka
Abstract: In the 1960s Cargo and Shisha introduced a metric in a family of quasi-arithmetic means defined on a common interval as the maximal possible difference between these means taken over all admissible vectors with corresponding weights. During the years 2013–2016 we proved that, having two quasi-arithmetic means, we can majorize the distance between them in terms of the Arrow–Pratt index. In this paper we are going to prove that this operator can also be used to establish certain lower bounds of this distance.
PubDate: 2017-10-11
DOI: 10.1007/s00010-017-0513-8

• Generalized poly-Cauchy and poly-Bernoulli numbers by using incomplete
$${\varvec{r}}$$ r -Stirling numbers
• Authors: Takao Komatsu; José L. Ramírez
Abstract: In this paper we introduce restricted r-Stirling numbers of the first kind. Together with restricted r-Stirling numbers of the second kind and the associated r-Stirling numbers of both kinds, by giving more arithmetical and combinatorial properties, we introduce a new generalization of incomplete poly-Cauchy numbers of both kinds and incomplete poly-Bernoulli numbers.
PubDate: 2017-10-11
DOI: 10.1007/s00010-017-0509-4

• Inequalities between remainders of quadratures
• Authors: Andrzej Komisarski; Szymon Wąsowicz
Abstract: It is well-known that in the class of convex functions the (nonnegative) remainder of the Midpoint Rule of approximate integration is majorized by the remainder of the Trapezoid Rule. Hence the approximation of the integral of a convex function by the Midpoint Rule is better than the analogous approximation by the Trapezoid Rule. Following this fact we examine remainders of certain quadratures in classes of convex functions of higher orders. Our main results state that for 3-convex (5-convex, respectively) functions the remainder of the 2-point (3-point, respectively) Gauss–Legendre quadrature is non-negative and it is not greater than the remainder of Simpson’s Rule (4-point Lobatto quadrature, respectively). We also check 2-point Radau quadratures for 2-convex functions to demonstrate that similar results fail to hold for convex functions of even orders. We apply the Peano Kernel Theorem as a main tool of our considerations.
PubDate: 2017-10-05
DOI: 10.1007/s00010-017-0505-8

• The projective translation equation and rational plane flows. II.
• Authors: Giedrius Alkauskas
Abstract: In this second part of the work, we correct the flaw which was left in the proof of the main Theorem in the first part. This affects only a small part of the text in this first part and two consecutive papers. Yet, some additional arguments are needed to claim the validity of the classification results. With these new results, algebraic and rational flows can be much more easily and transparently classified. It also turns out that the notion of an algebraic projective flow is a very natural one. For example, we give an inductive (on dimension) method to build algebraic projective flows with rational vector fields, and ask whether these account for all such flows. Further, we expand on results concerning rational flows in dimension 2. Previously we found all such flows symmetric with respect to a linear involution $$i_{0}(x,y)=(y,x)$$ . Here we find all rational flows symmetric with respect to a non-linear 1-homogeneous involution $$i(x,y)=(\frac{y^2}{x},y)$$ . We also find all solenoidal rational flows. Up to linear conjugation, there appears to be exactly two non-trivial examples.
PubDate: 2017-08-18
DOI: 10.1007/s00010-017-0500-0

second iterate
• Authors: Karol Baron
Abstract: Let E be a real inner product space of dimension at least 2. We show that both the set of all orthogonally additive functions mapping E into E having orthogonally additive second iterate and its complement are dense in the space of all orthogonally additive functions from E into E with the Tychonoff topology.
PubDate: 2017-08-17
DOI: 10.1007/s00010-017-0506-7

• On the shape of solution sets of systems of (functional) equations
• Authors: Endre Tóth; Tamás Waldhauser
Abstract: Solution sets of systems of linear equations over fields are characterized as being affine subspaces. But what can we say about the “shape” of the set of all solutions of other systems of equations' We study solution sets over arbitrary algebraic structures, and we give a necessary condition for a set of n-tuples to be the set of solutions of a system of equations in n unknowns over a given algebra. In the case of Boolean equations we obtain a complete characterization, and we also characterize solution sets of systems of Boolean functional equations.
PubDate: 2017-08-08
DOI: 10.1007/s00010-017-0499-2

• Affine planes over finite rings, a summary
• Authors: Dirk Keppens
Abstract: In Keppens (Innov. Incidence Geom. 15: 119–139, 2017) we gave a state of the art concerning “projective planes” over finite rings. The current paper gives a complementary overview for “affine planes” over rings (including the important subclass of desarguesian affine Klingenberg and Hjelmslev planes). No essentially new material is presented here but we give a summary of known results with special attention to the finite case, filling a gap in the literature.
PubDate: 2017-07-06
DOI: 10.1007/s00010-017-0497-4

• Category-measure duality: convexity, midpoint convexity and Berz
sublinearity
• Authors: N. H. Bingham; A. J. Ostaszewski
Abstract: Category-measure duality concerns applications of Baire-category methods that have measure-theoretic analogues. The set-theoretic axiom needed in connection with the Baire category theorem is the Axiom of Dependent Choice, DC rather than the Axiom of Choice, AC. Berz used the Hahn–Banach theorem over $${\mathbb {Q}}$$ to prove that the graph of a measurable sublinear function that is $${\mathbb {Q}}_{+}$$ -homogeneous consists of two half-lines through the origin. We give a category form of the Berz theorem. Our proof is simpler than that of the classical measure-theoretic Berz theorem, our result contains Berz’s theorem rather than simply being an analogue of it, and we use only DC rather than AC. Furthermore, the category form easily generalizes: the graph of a Baire sublinear function defined on a Banach space is a cone. The results are seen to be of automatic-continuity type. We use Christensen Haar null sets to extend the category approach beyond the locally compact setting where Haar measure exists. We extend Berz’s result from Euclidean to Banach spaces, and beyond. Passing from sublinearity to convexity, we extend the Bernstein–Doetsch theorem and related continuity results, allowing our conditions to be ‘local’—holding off some exceptional set.
PubDate: 2017-07-01
DOI: 10.1007/s00010-017-0486-7

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