1. Ph.D Theses
Permanent URI for this collectionhttps://idr.nitk.ac.in/handle/1/11
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Item Characterization of Non-Isolated Forts and Stability of an Iterative Functional Equation(National Institute of Technology Karnataka, Surathkal, 2021) Palanivel, R.; Murugan, V.The problem of finding a solution f : X →X of the iterative functional equation f n = F for a given positive integer n ≥ 2 and a function F : X → X on a non-empty set X is known as the iterative root problem. The non-strictly monotone points (or forts) of F play an essential role in finding a continuous solution f of f n = F whenever X is an interval in the real line. In this thesis, we define the forts for any continuous function f : I →J, where I and J are arbitrary intervals in the real line R. We study the non-monotone behavior of forts under composition and characterize the sets of isolated and non-isolated forts of iterates of any continuous self-map on an arbitrary interval I to study the continuous solutions of f n = F. Consequently, we obtain an example of an uncountable measure zero dense set of non-isolated forts in the real line. We define the notions of iteratively closed set in the space of continuous self-maps and the non-monotonicity height of any continuous self-map. We prove that continuous self-maps of non-monotonicity height 1 need not be strictly monotone on its range, unlike continuous piecewise monotone functions. Also, we obtain sufficient conditions for the existence of continuous solutions of f n = F for a class of continuous functions of non-monotonicity height 1. Further, we discuss the Hyers-Ulam stability of the iterative functional equation f n = F for continuous self-maps of non-monotonicity height 0 and 1.Item A Study on Semiclosed Subspaces and Semiclosed Operators in Hilbert Spaces(National Institute of Technology Karnataka, Surathkal, 2014) Balaji, S; Johnson, P. SamSemiclosed subspaces (para-closed subspaces, in the terminology of C. Fioas) of Hilbert spaces have been considered for a long time, as a more flexible substitute of closed subspaces of Hilbert spaces. What is even more interesting is that the notion of semiclosed subspace coincides with that of a Hilbert space continuously embedded in H. It is proved that the collection of all Hilbert spaces continuously embedded in a given Hilbert space H is in a bijective correspondence with the convex cone of all bounded positive self-adjoint operators in H. For two bounded operators A and B in H with the kernel condition N(A) ⊆ N(B), the quotient [B=A] defined in Izumino (1989), by Ax ! Bx, x 2 H. A quotient of bounded operators so defined is what was introduced by Kaufman (1978), as a \semiclosed operator", and several characterizations of it are given. It is proved that the family of quotients contains all closed operators and is itself closed under \sum" and \product". A merit for the quotient representation of a semiclosed operator is to make use of the theory of bounded operators. In the thesis, semiclosed subspaces and semiclosed operators in Hilbert spaces have been studied extensively.