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Jackson's Inequality
In approximation theory, Jackson's inequality is an inequality bounding the value of function's best approximation by algebraic or trigonometric polynomials in terms of the modulus of continuity or modulus of smoothness of the function or of its derivatives. Informally speaking, the smoother the function is, the better it can be approximated by polynomials. Statement: trigonometric polynomials For trigonometric polynomials, the following was proved by Dunham Jackson: :Theorem 1: If f: ,2\pito \C is an r times differentiable periodic function such that :: \left , f^(x) \right , \leq 1, \qquad x\in ,2\pi :then, for every positive integer n, there exists a trigonometric polynomial T_ of degree at most n-1 such that ::\left , f(x) - T_(x) \right , \leq \frac, \qquad x\in ,2\pi :where C(r) depends only on r. The Akhiezer– Krein– Favard theorem gives the sharp value of C(r) (called the Akhiezer–Krein–Favard constant): : C(r) = \frac \sum_^\infty \frac ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Approximation Theory
In mathematics, approximation theory is concerned with how function (mathematics), functions can best be approximation, approximated with simpler functions, and with quantitative property, quantitatively characterization (mathematics), characterizing the approximation error, errors introduced thereby. Note that what is meant by ''best'' and ''simpler'' will depend on the application. A closely related topic is the approximation of functions by generalized Fourier series, that is, approximations based upon summation of a series of terms based upon orthogonal polynomials. One problem of particular interest is that of approximating a function in a computer mathematical library, using operations that can be performed on the computer or calculator (e.g. addition and multiplication), such that the result is as close to the actual function as possible. This is typically done with polynomial or Rational function, rational (ratio of polynomials) approximations. The objective is to make t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Jean Favard
Jean Favard (28 August 190221 January 1965) was a French mathematician who worked on analysis. Favard was born in Peyrat-la-Nonière. During World War II he was a prisoner of war in Germany. He also was a President of the French Mathematical Society in 1946. He died in La Tronche, aged 62. See also * Favard measure (se * Bohr–Favard inequality (se * Favard inequality (se * Favard constant * Favard–Akhiezer–Krein theorem * Favard interpolation * Favard theorem * Favard problem (se * Favard operators External linksCOMITE DES AMIS DE JEAN-FAVARD*ThLycée Jean Favardis named after him. Favard is mentioned as a prisoner of war. * {{DEFAULTSORT:Favard, Jean 1902 births 1965 deaths Mathematical analysts 20th-century French mathematicians ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Approximation Theory
In mathematics, approximation theory is concerned with how function (mathematics), functions can best be approximation, approximated with simpler functions, and with quantitative property, quantitatively characterization (mathematics), characterizing the approximation error, errors introduced thereby. Note that what is meant by ''best'' and ''simpler'' will depend on the application. A closely related topic is the approximation of functions by generalized Fourier series, that is, approximations based upon summation of a series of terms based upon orthogonal polynomials. One problem of particular interest is that of approximating a function in a computer mathematical library, using operations that can be performed on the computer or calculator (e.g. addition and multiplication), such that the result is as close to the actual function as possible. This is typically done with polynomial or Rational function, rational (ratio of polynomials) approximations. The objective is to make t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Constructive Function Theory
In mathematical analysis, constructive function theory is a field which studies the connection between the smoothness of a function and its degree of approximation. It is closely related to approximation theory. The term was coined by Sergei Bernstein. Example Let ''f'' be a 2''π''-periodic function. Then ''f'' is ''α''- Hölder for some 0 < ''α'' < 1 if and only if for every natural ''n'' there exists a ''Pn'' of degree ''n'' such that : where ''C''(''f'') is a positive number depending on ''f''. The "only if" is due to , see |
Bernstein's Theorem (approximation Theory)
In approximation theory, Bernstein's theorem is a converse to Jackson's theorem. The first results of this type were proved by Sergei Bernstein in 1912. For approximation by trigonometric polynomials, the result is as follows: Let ''f'': , 2π → C be a 2''π''-periodic function, and assume ''r'' is a natural number, and 0 < ''α'' < 1. If there exists a number ''C''(''f'') > 0 and a sequence of s ''n'' ≥ ''n''0 such that : then ''f'' = ''P''''n''0 + ''φ'', where ''φ'' has a bounded ''r''-th derivative which is α-Hölder continuous. See also *[...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sergey Stechkin
Sergey Borisovich Stechkin (russian: Серге́й Бори́сович Сте́чкин) (6 September 1920 – 22 November 1995) was a prominent Soviet mathematician who worked in theory of functions (especially in approximation theory) and number theory. Biography Sergey Stechkin was born on 6 September 1920 in Moscow. His father (Boris Stechkin) was a Soviet turbojet engine designer, academician. His great uncle, N.Ye. Zhukovsky, was the founding father of modern aero- and hydrodynamics. His maternal grandfather, N.A. Shilov, was a notable chemist. His paternal grandfather was Sergey Solomin, a science fiction author. Stechkin attended school 58 and then attempted to matriculate to Moscow State University. He was turned down, likely due to the fact that the Soviet regime viewed his father as a political dissident at the time. He matriculated to Gorky State University instead. A year later, he was nevertheless able to transfer to the Mechanics and Mathematics department ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Antoni Zygmund
Antoni Zygmund (December 25, 1900 – May 30, 1992) was a Polish mathematician. He worked mostly in the area of mathematical analysis, including especially harmonic analysis, and he is considered one of the greatest analysts of the 20th century. Zygmund was responsible for creating the Chicago school of mathematical analysis together with his doctoral student Alberto Calderón, for which he was awarded the National Medal of Science in 1986. Biography Born in Warsaw, Zygmund obtained his Ph.D. from the University of Warsaw (1923) and was a professor at Stefan Batory University at Wilno from 1930 to 1939, when World War II broke out and Poland was occupied. In 1940 he managed to emigrate to the United States, where he became a professor at Mount Holyoke College in South Hadley, Massachusetts. In 1945–1947 he was a professor at the University of Pennsylvania, and from 1947, until his retirement, at the University of Chicago. He was a member of several scientific societies. Fro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Favard Constant
In mathematics, the Favard constant, also called the Akhiezer–Krein–Favard constant, of order ''r'' is defined as :K_r = \frac \sum\limits_^ \left \frac \right. This constant is named after the French mathematician Jean Favard, and after the Soviet mathematicians Naum Akhiezer and Mark Krein. Particular values :K_0 = 1. :K_1 = \frac. Uses This constant is used in solutions of several extremal problems, for example * Favard's constant is the sharp constant in Jackson's inequality for trigonometric polynomials * the sharp constants in the Landau–Kolmogorov inequality are expressed via Favard's constants * Norms of periodic perfect spline Perfect commonly refers to: * Perfection, completeness, excellence * Perfect (grammar), a grammatical category in some languages Perfect may also refer to: Film * Perfect (1985 film), ''Perfect'' (1985 film), a romantic drama * Perfect (2018 f ...s. References * Mathematical constants {{mathanalysis-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mark Krein
Mark Grigorievich Krein ( uk, Марко́ Григо́рович Крейн, russian: Марк Григо́рьевич Крейн; 3 April 1907 – 17 October 1989) was a Soviet mathematician, one of the major figures of the Soviet school of functional analysis. He is known for works in operator theory (in close connection with concrete problems coming from mathematical physics), the problem of moments, classical analysis and representation theory. He was born in Kyiv, leaving home at age 17 to go to Odessa. He had a difficult academic career, not completing his first degree and constantly being troubled by anti-Semitic discrimination. His supervisor was Nikolai Chebotaryov. He was awarded the Wolf Prize in Mathematics in 1982 (jointly with Hassler Whitney), but was not allowed to attend the ceremony. David Milman, Mark Naimark, Israel Gohberg, Vadym Adamyan, Mikhail Livsic and other known mathematicians were his students. He died in Odessa. On 14 January 2008, the memo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polynomials
In mathematics, a polynomial is an expression (mathematics), expression consisting of indeterminate (variable), indeterminates (also called variable (mathematics), variables) and coefficients, that involves only the operations of addition, subtraction, multiplication, and positive-integer powers of variables. An example of a polynomial of a single indeterminate is . An example with three indeterminates is . Polynomials appear in many areas of mathematics and science. For example, they are used to form polynomial equations, which encode a wide range of problems, from elementary word problem (mathematics education), word problems to complicated scientific problems; they are used to define polynomial functions, which appear in settings ranging from basic chemistry and physics to economics and social science; they are used in calculus and numerical analysis to approximate other functions. In advanced mathematics, polynomials are used to construct polynomial rings and algebraic variety ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Naum Akhiezer
Naum Ilyich Akhiezer ( uk, Нау́м Іллі́ч Ахіє́зер; russian: link=no, Нау́м Ильи́ч Ахие́зер; 6 March 1901 – 3 June 1980) was a Soviet and Ukrainian mathematician of Jewish origin, known for his works in approximation theory and the theory of differential and integral operators.NAUM IL’ICH AKHIEZER (ON THE 100TH ANNIVERSARY OF HIS BIRTH), by V. A. Marchenko, Yu. A. Mitropol’skii, A. V. Pogorelov, A. M. Samoilenko, I. V. Skrypnik, and E. Ya. Khruslov (restricted access) He is also known as the author of classical books on various subjects in |
Trigonometric Polynomial
In the mathematical subfields of numerical analysis and mathematical analysis, a trigonometric polynomial is a finite linear combination of functions sin(''nx'') and cos(''nx'') with ''n'' taking on the values of one or more natural numbers. The coefficients may be taken as real numbers, for real-valued functions. For complex coefficients, there is no difference between such a function and a finite Fourier series. Trigonometric polynomials are widely used, for example in trigonometric interpolation applied to the interpolation of periodic functions. They are used also in the discrete Fourier transform. The term ''trigonometric polynomial'' for the real-valued case can be seen as using the analogy: the functions sin(''nx'') and cos(''nx'') are similar to the monomial basis for polynomials. In the complex case the trigonometric polynomials are spanned by the positive and negative powers of ''e''''ix'', Laurent polynomials in ''z'' under the change of variables ''z'' = ''e''''ix' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
