What is it about?

It gives me great pleasure to introduce as well as discuss, learn, solve, teach, and work with operator theory. This book discusses some fundamental aspects of the theory of operators and explores their use to solve a large array of problems. The book addresses many topics, including the paradigm of complex probability, principal parts extension for a Noether operator A, the sets of fractional operators and some of their applications, the total and partial differentials as algebraically manipulable entities, and more. In mathematics, operator theory is the study of linear operators on function spaces, beginning with differential operators and integral operators. The operators may be presented abstractly by their characteristics, such as bounded linear operators or closed operators; consideration may also be given to nonlinear operators. The study of operator theory, which depends heavily on the topology of function spaces, is a branch of functional analysis. Also, if a collection of operators forms an algebra over a field, then it is an operator algebra. Hence, the description of operator algebras is part of operator theory. Moreover, single-operator theory deals with the properties and classification of operators, considered one at a time. For example, the classification of normal operators in terms of their spectra falls into this category. In addition, the theory of operator algebras brings algebras of operators such as C*-algebras to the fore. Many operators that are studied are operators on Hilbert spaces of holomorphic functions, and the study of the operator is intimately linked to questions in function theory. For example, Beurling’s theorem describes the invariant subspaces of the unilateral shift in terms of inner functions, which are bounded holomorphic functions on the unit disk with unimodular boundary values almost everywhere on the circle. Beurling interpreted the unilateral shift as multiplication by the independent variable on the Hardy space. The success in studying multiplication operators, and more generally Toeplitz operators (which are multiplication, followed by projection onto the Hardy space), has inspired the study of similar questions in other spaces, such as the Bergman space. Therefore, operator theory has a connection with complex analysis. This volume illustrates the use of operator theory when applied to solve specific problems and discusses some fundamental aspects of pure and applied operator theory. It is a useful resource for scholars, researchers, and undergraduate and graduate students in pure and applied mathematics, classical and modern physics, engineering, and science in general.

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Why is it important?

Operator theory is a fascinating model that includes essential theorems and diverse applications in all science. This book discusses some fundamental aspects of pure and applied operator theory and the use of the theory to solve a large array of problems. As such, it will be of interest to scholars, researchers, and undergraduate and graduate students in pure and applied mathematics, classical and modern physics, engineering, and science in general.

Perspectives

Although I have taught courses on probability and statistics at the university level for many years, I consider myself a beginner in this branch of knowledge; in fact an absolute beginner, always thirsty to learn and discover more. I think that the mathematician who proves to be successful in tackling and mastering the theory of probability and statistics has made it halfway to understanding the mystery of existence revealed in a universe governed sometimes in our modern theories by randomness and uncertainties. The probabilistic aspect is evident in the theories of the quantum world, of thermodynamics, or of statistical mechanics, for example. Hence, the universe’s secret code, I think, is written in a mathematical language, just as Galileo Galilei expressed it in these words: “Philosophy is written in this very great book which is the universe that always lies open before our eyes. One cannot understand this book unless one first learns to understand the language and recognize the characters in which it is written. It is written in a mathematical language and the characters are triangles, circles and other geometrical figures. Without these means it is humanly impossible to understand a word of it. Without these there is only clueless scrabbling around in a dark labyrinth.”

Dr. Abdo Abou Jaoude
Notre Dame University Louaize

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This page is a summary of: Operator Theory - Recent Advances, New Perspectives and Applications, May 2023, IntechOpen,
DOI: 10.5772/intechopen.102221.
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