arXiv subjects
Publications and source records attributed to Alexandru Mihail.
This paper provides an alternative description for the fixed points of the fractal operator associated with a mixed possibly infinite iterated function system via a canonical projection type function. Some visual aspects of our results are presented.
Orbital fuzzy iterated function systems are obtained as a combination of the concepts of iterated fuzzy set system and orbital iterated function system. It turns out that, for such a system, the corresponding fuzzy operator is weakly Picard, its fixed points being called fuzzy fractals. In this paper we present a structure result concerning fuzzy fractals associated to an orbital fuzzy iterated function system by proving that such an object is perfectly determined by the action of the initial term of the Picard iteration sequence on the closure of the orbits of certain elements.
In this paper we introduce the concept of orbital fuzzy iterated function system and prove that the fuzzy operator associated to such a system is weakly Picard. An example is provided.
In this paper we introduce the notions of phi-contractive parent-child infinite iterated function system (pcIIFS) and orbital phi-contractive infinite iterated function system (oIIFS) and we prove that the corresponding fractal operator is weakly Picard. The corresponding notions of shift space, canonical projection and their properties are also treated.
In this paper we introduce the notion of diameter diminishing to zero iterated function system, study its properties and provide alternative characterizations of it.
We provide a new algorithm (called the grid algorithm) designed to generate the image of the attractor of a generalized iterated function system on a finite dimensional space and we compare it with the deterministic algorithm regarding generalized iterated function systems presented by P. Jaros, L. Maslanka and F. Strobin in [Algorithms generating images of attractors of generalized iterated function systems, Numer. Algorithms, 73 (2016), 477-499].
We prove that the Markov operator associated to an iterated function system consisting of phi-max-contractions with probabilities has a unique invariant measure whose support is the attractor of the system.
We associate to each iterated function system consisting of phi-max-contractions an operator (on the space of continuous functions from the shift space on the metric space corresponding to the system) having a unique fixed point whose image turns out to be the attractor of the system. Moreover, we prove that the unique fixed point of the operator associated to an iterated function system consisting of convex contractions is the canonical projection from the shift space on the attractor of the system.
Taking as model the attractor of an iterated function system consisting of phi-contractions on a complete and bounded metric space, we introduce the set-theoretic concept of family of functions having attractor. We prove that, given such a family, there exist a metric on the set on which the functions are defined and take values and a comparison function phi such that all the family's functions are phi-contractions. In this way we obtain a generalization for a finite family of functions of the converse of Browder's fixed point theorem. As byproducts we get a particular case of Bessaga's theorem concerning the converse of the contraction principle and a companion of Wong's result which extends the above mentioned Bessaga's result for a finite family of commuting functions with common fixed point.
In this paper we prove a generalization of Istrăţescu's theorem for convex contractions. More precisely, we introduce the concept of iterated function system consisting of convex contractions and prove the existence and uniqueness of the attractor of such a system. In addition we study the properties of the canonical projection from the code space into the attractor of an iterated function system consisting of convex contractions.
In this paper we obtain a generalization of Matkowski's fixed point theorem and Istratescu's fixed point theorem concerning convex contractions in the framework of b-metric spaces. By providing appropriate examples we show that the above mentioned two generalizations are effective.
In this paper we indicate a way to generalize a series of fixed point results in the framework of b-metric spaces and we exemplify it by extending Nadler's contraction principle for set-valued functions (see Multi-valued contraction mappings, Pac. J. Math., 30 (1969), 475-488) and a fixed point theorem for set-valued quasi-contractions functions due to H. Aydi, M.F. Bota, E. Karapinar and S. Mitrovic (see A fixed point theorem for set-valued quasi-contractions in b-metric spaces, Fixed Point Theory Appl. 2012, 2012:88).
In this paper, based on a lemma giving a sufficient condition for a sequence with elements from a b-metric space to be Cauchy, we obtain Caristi-Kirk type and Boyd&Wong-Browder-Matkowski-Rus type fixed point results in the framework of b-metric spaces. In addition, we extend Theorems 1,2 and 3 from [M. Bota,V. Ilea, E. Karapinar, O. Mlesnite, On alpha-star-phi-contractive multi-valued operators in b-metric spaces and applications, Applied Mathematics & Information Sciences, 9 (2015), 2611-2620].
In one of our previous papers we proved that, for an infinite set A and p\in[1,\infty), the embedded version of the Lipscomb's space L(A) in l^{p}(A), p\in[1,\infty), with the metric induced from l^{p}(A), denoted by ω_{p}^{A}, is the attractor of an infinite iterated function system comprising affine transformations of l^{p}(A). In the present paper we point out that ω_{p}^{A}=ω_{q}^{A}, for all p,q\in[1,\infty) and, by providing a complete description of the convergent sequences from ω_{p}^{A}, we prove that the topological structure of ω_{p}^{A} is independent of p.
In this paper we present a result which establishes a connection between the theory of compact operators and the theory of iterated function systems. For a Banach space X, S and T bounded linear operators from X to X such that \parallel S \parallel, \parallel T \parallel <1 and w \in X, let us consider the IFS S_{w}=(X,f_1,f_2), where f_1,f_2:X \rightarrow X are given by f_1(x)=S(x) and f_2(x)=T(x)+w, for all x \in X. On one hand we prove that if the operator S is compact, then there exists a family (K_{n})_{n \in N} of compact subsets of X such that A_{S_{w}} is not connected, for all w \in H- \cup K_{n}. One the other hand we prove that if H is an infinite dimensional Hilbert space, then a bounded linear operator S:H \rightarrow H having the property that \parallel S \parallel <1 is compact provided that for every bounded linear operator T:H\rightarrow H such that \parallel T \parallel <1 there exists a sequence (K_{T,n})_{n} of compact subsets of H such that A_{S_{w}} is not connected for all w \in H- \cup K_{T,n}. Consequently, given an infinite dimensional Hilbert space H, there exists a complete characterization of the compactness of an operator S:H \rightarrow H by means of the non-connectedness of the attractors of a family of IFSs related to the given operator.