Hormander Operators


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Hormander Operators


Hormander Operators

Author: Marco Bramanti

language: en

Publisher: World Scientific

Release Date: 2022-10-21


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Hörmander operators are a class of linear second order partial differential operators with nonnegative characteristic form and smooth coefficients, which are usually degenerate elliptic-parabolic, but nevertheless hypoelliptic, that is highly regularizing. The study of these operators began with the 1967 fundamental paper by Lars Hörmander and is intimately connected to the geometry of vector fields.Motivations for the study of Hörmander operators come for instance from Kolmogorov-Fokker-Planck equations arising from modeling physical systems governed by stochastic equations and the geometric theory of several complex variables. The aim of this book is to give a systematic exposition of a relevant part of the theory of Hörmander operators and vector fields, together with the necessary background and prerequisites.The book is intended for self-study, or as a reference book, and can be useful to both younger and senior researchers, already working in this area or aiming to approach it.

Fundamental Solutions and Local Solvability for Nonsmooth Hormander's Operators


Fundamental Solutions and Local Solvability for Nonsmooth Hormander's Operators

Author: Marco Bramanti

language: en

Publisher: American Mathematical Soc.

Release Date: 2017-09-25


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The authors consider operators of the form in a bounded domain of where are nonsmooth Hörmander's vector fields of step such that the highest order commutators are only Hölder continuous. Applying Levi's parametrix method the authors construct a local fundamental solution for and provide growth estimates for and its first derivatives with respect to the vector fields. Requiring the existence of one more derivative of the coefficients the authors prove that also possesses second derivatives, and they deduce the local solvability of , constructing, by means of , a solution to with Hölder continuous . The authors also prove estimates on this solution.

An Invitation to Hypoelliptic Operators and Hörmander's Vector Fields


An Invitation to Hypoelliptic Operators and Hörmander's Vector Fields

Author: Marco Bramanti

language: en

Publisher: Springer Science & Business Media

Release Date: 2013-11-20


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​Hörmander's operators are an important class of linear elliptic-parabolic degenerate partial differential operators with smooth coefficients, which have been intensively studied since the late 1960s and are still an active field of research. This text provides the reader with a general overview of the field, with its motivations and problems, some of its fundamental results, and some recent lines of development.