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1
Local stationary heat fields in fibrous composites
EN
Consider a multiply connected domain D bounded by nonoverlapping circles. Introduce the complex potential u(z) = Re ϕ(z) in D where the function ϕ(z) is analytic in D except at infinity where ϕ(z) ∼ z. The function u(z) models the distribution of temperature in the domain D. The unknown function ϕ(z) is continuously differentiable in the closures of the considered domain. We solve approximately the modified Schwarz problem when u(z) = Re ϕ(z) is equal to an undetermined constant on every boundary component of D by a method of functional equations.
2
On two functional equations connected with distributivity of fuzzy implications
EN
The distributivity law for a fuzzy implication I:[0,1]2→[0,1] with respect to a fuzzy disjunction S:[0,1]2→[0,1] states that the functional equation I(x,S(y,z))=S(I(x,y),I(x,z)) is satisfied for all pairs (x,y) from the unit square. To compare some results obtained while solving this equation in various classes of fuzzy implications, Wanda Niemyska has reduced the problem to the study of the following two functional equations: h(min(xg(y),1))=min(h(x)+h(xy),1), x∈(0,1), y∈(0,1], and h(xg(y))=h(x)+h(xy), x,y∈(0,∞), in the class of increasing bijections h:[0,1]→[0,1] with an increasing function g:(0,1]→[1,∞) and in the class of monotonic bijections h:(0,∞)→(0,∞) with a function g:(0,∞)→(0,∞), respectively. A description of solutions in more general classes of functions (including nonmeasurable ones) is presented.
EN
We deal with a functional equation of the form ƒ(x + y) = F(ƒ(x), ƒ(y)) (so called addition formula) assuming that the given binary operation F is associative but its domain is not connected. The aim of the present paper is to discuss solutions of the equation [formula]. It turns out that this functional equation characterized an inverse proportionality type function, but if the domain of the unknown function has no neutral element. In this paper we admit fairly general structure in the domain of the unknown function.
EN
For h : (0,∞) → R, the function h* (t) := th( 1/t ) is called (*)-conjugate to h. This conjugacy is related to the Hölder and Minkowski inequalities. Several properties of (*)-conjugacy are proved. If φ and φ* are bijections of (0,∞) then [formula]. Under some natural rate of growth conditions at 0 and ∞, if φ is increasing, convex, geometrically convex, then [formula] has the same properties. We show that the Young conjugate functions do not have this property. For a measure space (Ω,Σ,μ) denote by S = (Ω,Σ,μ) the space of all μ-integrable simple functions x : Ω → R, Given a bijection φ : (0,∞) → (0,∞) define [formula] by [formula] where Ω(x) is the support of x. Applying some properties of the (*) operation, we prove that if ƒ xy ≤ Pφ(x)Pψ (y) where [formula] and [formula] are conjugate, then φ and ψ are conjugate power functions. The existence of nonpower bijections φ and ψ with conjugate inverse functions [formula] such that Pφ and Pψ are subadditive and subhomogeneous is considered.
5
A counterpart of the Taylor theorem and means
EN
For an n-times differentiable real function ƒ defined in an a real interval I, some properties of the Taylor remainder means Tn[ƒ] are considered. It is proved that Tn[ƒ] is symmetric iff n – 1, and a conjecture concerning the equality Tn[g]- Tn[ƒ] is formulated. The main result says that if ƒ (n) is one-to-one, there exists a unique mean Mn[ƒ] : ƒ(n) (I) x ƒ(n) (I) → ƒ(n) (I) such that, for all x, y ϵ I, …[wzór]. The connection between Tnƒ ana Mnƒ is given. A functional equation related to M2 ƒ is derived and an open problem is posed.
EN
This work deals with the Feigenbaum's functional equation in the broad sense (…), where φ2 is the 2-fold iteration of φ, f(x) is a strictly increasing continuous function on [0, 1] and satisfies (...). Using constructive method, we discuss the existence of single-valley-extended continuous solutions of the above equation.
EN
Inspired by some relevant recent results of A. E. Abbas we determine utility functions invariant with respect to some classes of transformations.
EN
In the present paper we deal with the Dhombres-type trigonometric difference f(x + y 2 )2 – f(x − y 2)2 + f(x + y) + f(x − y) − f(x) [f(y) + g(y)], assuming that its absolute value is majorized by some constant. Our aim is to find functions and which satisfy the Dhombres-type trigonometric functional equation and for which the differences f - f and g - g are uniformly bounded.
EN
We deal with the functional equation (so called addition formula) of the form f(x + y) = F(f(x),f(y)), where F is an associative rational function. The class of associative rational functions was described by A. Chéritat [1] and his work was followed by a paper of the author. For function F deﬁned by F(x,y) = ϕ−1(ϕ(x) + ϕ(y)), where ϕ is a homographic function, the addition formula is fulﬁlled by homographic type functions. We consider the class of the associative rational functions defined by formula F(u,v) =uv αuv + u + v, where α is a ﬁxed real numer.
EN
Let (G, +) be a uniquely 2-divisible Abelian group. In the present paper we will consider the solutions of functional equation [f(x + y)]2 - [f(x - y)]2 + f(2x + 2y) + f(2x - 2y) = f(2x)[f(2y) + 2g(2y)], x,y ϵ G, where f and g are complex-valued functions defined on G.
11
A characterization of a homographic type function II
EN
This article is a continuation of the investigations contained in the previous paper [2]. We deal with the following conditional functional equation: [wzór] implies [wzór] with λ ≠ 0.
EN
Composite functional equations in several variables generalizing the Gołąb-Schinzel equation are considerd and some simple methods allowing us to determine their one-to-one solutions, bijective solutions or the solutions having exactly one zero are presented. For an arbitrarily fixed real p, the functional equation Φ([pφ(y) + (1−p)]x +[(1−p)φ(x)+p]y) = φ(x)φ(y), x,y ∈ R, being a special generalization of the Gołąb-Schinzel equation, is considered.
13
A characterization of a homographic type function
EN
We deal with a functional equation of the form f(x + y) = F(f(x),f(y)) (the so called addition formula) assuming that the given binary operation F is associative but its domain of definition is not necessarily connected. In the present paper we shall restrict our consideration to the case when [formula]. These considerations may be viewed as counter parts of Losonczi's [7] and Domańska's [3] results on local solutions of the functional equation f(F(x, y)) = f(x) + f(y) with the same behaviour of the given associative operation F. In this paper we admit fairly general structure in the domain of the unknown function.
EN
The continuous solutions of a composite functional equation are characterized. An applications to the problem of invariant curves is presented.
EN
Some sufficient conditions which allow to extend every local solution of a simultaneous system of equations in a single variable of the form φ(x)=h(x, φ[ƒ1(x)],…, φ[ƒm(x)]) φ(x)=H(x,φ[F1(x),…, [Fn(x)]) to a global one are presented. Extensions of solutions of functional equations, both in single and in several variables, play important role (cf. for instance [1-3]).
EN
An extension theorem for the functional equation of several variables ƒ (M(x,y))=N(ƒ(x), ƒ (y)), where the given functions M and N are left-side autodistributive, is presented.
EN
In this paper, we show that the paper mentioned in the title includes some wrong results. We also provide a counter example.
EN
The general solutions of a sum form functional equation have been obtained. The importance of its solutions in relation to the entropies and some moments of a discrete random variable has been discussed.
EN
We prove that all assumptions of a Theorem of Forti and Schwaiger (cf. [4]) on the coherence of stability of the equation of homomorphism with the completeness of the space of values of all these homomorphisms, are essential. We give some generalizations of this theorem and certain examples of applications.
20
On solutions of a generalization of the Reynolds functional equation
EN
Let (X, .) be a group endowed with a topology and F : C - X. Under some assumptions on X and F, we describe the solutions f : X - > C of the functional equation f(F(y)) . x)=f(y)f(x), that are continuous at a point or (universally, Baire, Christensen or Haar) measurable. We also show some consequences of those results.
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