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Sharkovskiĭ's theorem holds for some discontinuous functions

Piotr Szuca (2003)

Fundamenta Mathematicae

We show that the Sharkovskiĭ ordering of periods of a continuous real function is also valid for every function with connected G δ graph. In particular, it is valid for every DB₁ function and therefore for every derivative. As a tool we apply an Itinerary Lemma for functions with connected G δ graph.

Some dynamical properties of S-unimodal maps

Tomasz Nowicki (1993)

Fundamenta Mathematicae

We study 1) the slopes of central branches of iterates of S-unimodal maps, comparing them to the derivatives on the critical trajectory, 2) the hyperbolic structure of Collet-Eckmann maps estimating the exponents, and under a summability condition 3) the images of the density one under the iterates of the Perron-Frobenius operator, 4) the density of the absolutely continuous invariant measure.

Subadditive functions and partial converses of Minkowski's and Mulholland's inequalities

J. Matkowski, T. Świątkowski (1993)

Fundamenta Mathematicae

Let ϕ be an arbitrary bijection of + . We prove that if the two-place function ϕ - 1 [ ϕ ( s ) + ϕ ( t ) ] is subadditive in + 2 then ϕ must be a convex homeomorphism of + . This is a partial converse of Mulholland’s inequality. Some new properties of subadditive bijections of + are also given. We apply the above results to obtain several converses of Minkowski’s inequality.

Substitution systems associated with the dynamical system (𝒜, Tf)*

Maria de Fátima Correia, Carlos Ramos, Sandra Vinagre (2012)

ESAIM: Proceedings

We consider the dynamical system (𝒜, Tf), where 𝒜 is a class of differential real functions defined on some interval and Tf : 𝒜 → 𝒜 is an operator Tfφ := fοφ, where f is a differentiable m-modal map. If we consider functions in 𝒜 whose critical values are periodic points for f then, we show how to define and characterize a substitution system associated with (𝒜, Tf). For these substitution systems, we compute the growth rate of the...

The continuous solutions of a generalized Dhombres functional equation

L. Reich, Jaroslav Smítal, M. Štefánková (2004)

Mathematica Bohemica

We consider the functional equation f ( x f ( x ) ) = ϕ ( f ( x ) ) where ϕ J J is a given increasing homeomorphism of an open interval J ( 0 , ) and f ( 0 , ) J is an unknown continuous function. In a series of papers by P. Kahlig and J. Smítal it was proved that the range of any non-constant solution is an interval whose end-points are fixed under ϕ and which contains in its interior no fixed point except for 1 . They also provide a characterization of the class of monotone solutions and prove a necessary and sufficient condition for any solution...

The converse problem for a generalized Dhombres functional equation

L. Reich, Jaroslav Smítal, M. Štefánková (2005)

Mathematica Bohemica

We consider the functional equation f ( x f ( x ) ) = ϕ ( f ( x ) ) where ϕ J J is a given homeomorphism of an open interval J ( 0 , ) and f ( 0 , ) J is an unknown continuous function. A characterization of the class 𝒮 ( J , ϕ ) of continuous solutions f is given in a series of papers by Kahlig and Smítal 1998–2002, and in a recent paper by Reich et al. 2004, in the case when ϕ is increasing. In the present paper we solve the converse problem, for which continuous maps f ( 0 , ) J , where J is an interval, there is an increasing homeomorphism ϕ of J such that f 𝒮 ( J , ϕ ) . We...

The Covering Principle for Darboux Baire 1 functions

Piotr Szuca (2007)

Fundamenta Mathematicae

We show that the Covering Principle known for continuous maps of the real line also holds for functions whose graph is a connected G δ subset of the plane. As an application we find an example of an approximately continuous (hence Darboux Baire 1) function f: [0,1] → [0,1] such that any closed subset of [0,1] can be translated so as to become an ω-limit set of f. This solves a problem posed by Bruckner, Ceder and Pearson [Real Anal. Exchange 15 (1989/90)].

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