Главная    Ex Libris    Книги    Журналы    Статьи    Серии    Каталог    Wanted    Загрузка    ХудЛит    Справка    Поиск по индексам    Поиск    Форум   
blank
Авторизация

       
blank
Поиск по указателям

blank
blank
blank
Красота
blank
Márton Elekes, Miklós Laczkovich — A cardinal number connected to the solvability of systems of difference equations in a given function class
Márton Elekes, Miklós Laczkovich — A cardinal number connected to the solvability of systems of difference equations in a given function class

Читать книгу
бесплатно

Скачать книгу с нашего сайта нельзя

Обсудите книгу на научном форуме



Нашли опечатку?
Выделите ее мышкой и нажмите Ctrl+Enter


Название: A cardinal number connected to the solvability of systems of difference equations in a given function class

Авторы: Márton Elekes, Miklós Laczkovich

Аннотация:

Let ℝℝ denote the set of real valued functions defined on the real line. A map D: ℝℝ → ℝℝ is said to be a difference operator if there are real numbers a i, b i (i = 1, …, n) such that (Dƒ)(x) = ∑ i=1 n a i ƒ(x + b i) for every ƒ ∈ ℝℝand x ∈ ℝ. By a system of difference equations we mean a set of equations S = {D i ƒ = g i: i ∈ I}, where I is an arbitrary set of indices, D i is a difference operator and g i is a given function for every i ∈ I, and ƒ is the unknown function. One can prove that a system S is solvable if and only if every finite subsystem of S is solvable. However, if we look for solutions belonging to a given class of functions then the analogous statement is no longer true. For example, there exists a system S such that every finite subsystem of S has a solution which is a trigonometric polynomial, but S has no such solution; moreover, S has no measurable solutions. This phenomenon motivates the following definition. Let be a class of functions. The solvability cardinal sc( ) of is the smallest cardinal number κ such that whenever S is a system of difference equations and each subsystem of S of cardinality less than κ has a solution in , then S itself has a solution in . In this paper we determine the solvability cardinals of most function classes that occur in analysis. As it turns out, the behaviour of sc( ) is rather erratic. For example, sc(polynomials) = 3 but sc(trigonometric polynomials) = ω 1, sc({ƒ: ƒ is continuous}) = ω 1 but sc({f : f is Darboux}) = (2 ω )+, and sc(ℝℝ) = ω. We consistently determine the solvability cardinals of the classes of Borel, Lebesgue and Baire measurable functions, and give some partial answers for the Baire class 1 and Baire class α functions.


Язык: en

Рубрика: Математика/

Тип: Статья

Статус предметного указателя: Неизвестно

ed2k: ed2k stats

Год издания: 2006

Количество страниц: 20

Добавлена в каталог: 22.07.2009

Операции: Положить на полку | Скопировать ссылку для форума | Скопировать ID
blank
Предметный указатель
blank
Реклама
blank
blank
HR
@Mail.ru
       © Электронная библиотека попечительского совета мехмата МГУ, 2004-2018
Электронная библиотека мехмата МГУ | Valid HTML 4.01! | Valid CSS! О проекте