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Freiman's Theorem
In additive combinatorics, a discipline within mathematics, Freiman's theorem is a central result which indicates the approximate structure of sets whose sumset is small. It roughly states that if , A+A, /, A, is small, then A can be contained in a small generalized arithmetic progression. Statement If A is a finite subset of \mathbb with , A+A, \le K, A, , then A is contained in a generalized arithmetic progression of dimension at most d(K) and size at most f(K), A, , where d(K) and f(K) are constants depending only on K. Examples For a finite set A of integers, it is always true that :, A + A, \ge 2, A, -1, with equality precisely when A is an arithmetic progression. More generally, suppose A is a subset of a finite proper generalized arithmetic progression P of dimension d such that , P, \le C, A, for some real C \ge 1. Then , P+P, \le 2^d , P, , so that :, A+A, \le , P+P, \le 2^d , P, \le C2^d, A, . History of Freiman's theorem This result is due to Gregory Freim ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Additive Combinatorics
Additive combinatorics is an area of combinatorics in mathematics. One major area of study in additive combinatorics are ''inverse problems'': given the size of the sumset is small, what can we say about the structures of and ? In the case of the integers, the classical Freiman's theorem provides a partial answer to this question in terms of multi-dimensional arithmetic progressions. Another typical problem is to find a lower bound for in terms of and . This can be viewed as an inverse problem with the given information that is sufficiently small and the structural conclusion is then of the form that either or is the empty set; however, in literature, such problems are sometimes considered to be direct problems as well. Examples of this type include the Erdős–Heilbronn Conjecture (for a restricted sumset) and the Cauchy–Davenport Theorem. The methods used for tackling such questions often come from many different fields of mathematics, including combinatorics, ergod ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Geometry Of Numbers
Geometry of numbers is the part of number theory which uses geometry for the study of algebraic numbers. Typically, a ring of algebraic integers is viewed as a lattice (group), lattice in \mathbb R^n, and the study of these lattices provides fundamental information on algebraic numbers. initiated this line of research at the age of 26 in his work ''The Geometry of Numbers''. The geometry of numbers has a close relationship with other fields of mathematics, especially functional analysis and Diophantine approximation, the problem of finding rational numbers that approximate an irrational number, irrational quantity. Minkowski's results Suppose that \Gamma is a Lattice (group), lattice in n-dimensional Euclidean space \mathbb^n and K is a convex centrally symmetric body. Minkowski's theorem, sometimes called Minkowski's first theorem, states that if \operatorname (K)>2^n \operatorname(\mathbb^n/\Gamma), then K contains a nonzero vector in \Gamma. The successive minimum \lamb ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kneser's Theorem (combinatorics)
In the branch of mathematics known as additive combinatorics, Kneser's theorem can refer to one of several related theorems regarding the sizes of certain sumsets in abelian groups. These are named after Martin Kneser, who published them in 1953 and 1956. They may be regarded as extensions of the Cauchy–Davenport theorem, which also concerns sumsets in groups but is restricted to groups whose order is a prime number. The first three statements deal with sumsets whose size (in various senses) is strictly smaller than the sum of the size of the summands. The last statement deals with the case of equality for Haar measure in connected compact abelian groups. Strict inequality If G is an abelian group and C is a subset of G , the group H(C):= \ is the ''stabilizer'' of C . Cardinality Let G be an abelian group. If A and B are nonempty finite subsets of G satisfying , A + B, < , A, + , B, and is the stabilizer of [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Plünnecke–Ruzsa Inequality
In additive combinatorics, the Plünnecke–Ruzsa inequality is an inequality that bounds the size of various sumsets of a set B, given that there is another set A so that A+B is not much larger than A. A slightly weaker version of this inequality was originally proven and published by Helmut Plünnecke (1970). Imre Ruzsa (1989) later published a simpler proof of the current, more general, version of the inequality. The inequality forms a crucial step in the proof of Freiman's theorem. Statement The following sumset notation is standard in additive combinatorics. For subsets A and B of an abelian group and a natural number k, the following are defined: * A+B=\ * A-B=\ * kA=\underbrace_ The set A + B is known as the sumset of A and B. Plünnecke-Ruzsa inequality The most commonly cited version of the statement of the Plünnecke–Ruzsa inequality is the following. This is often used when A = B, in which case the constant K = , 2A, /, A, is known as the doubling constant of A ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Markov Spectrum
In mathematics, the Markov spectrum, devised by Andrey Markov, is a complicated set of real numbers arising in Markov Diophantine equations and also in the theory of Diophantine approximation. Quadratic form characterization Consider a quadratic form given by ''f''(''x'',''y'') = ''ax''2 + ''bxy'' + ''cy''2 and suppose that its discriminant is fixed, say equal to −1/4. In other words, ''b''2 − 4''ac'' = 1. One can ask for the minimal value achieved by \left\vert f(x,y) \right\vert when it is evaluated at non-zero vectors of the grid \mathbb^2, and if this minimum does not exist, for the infimum. The Markov spectrum ''M'' is the set obtained by repeating this search with different quadratic forms with discriminant fixed to −1/4:M = \left\ Lagrange spectrum Starting from Hurwitz's theorem on Diophantine approximation, that any real number \xi has a sequence of rational approximations ''m''/''n'' tending to it with :\left , \xi-\frac\right , <\frac, [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lean (proof Assistant)
Lean is a proof assistant and a Functional programming, functional programming language. It is based on the calculus of constructions with inductive types. It is an open-source project hosted on GitHub. Development is currently supported by the Nonprofit organization, non-profit Lean Focused Research Organization, Focused Research Organization (FRO). History Lean was developed primarily by Leonardo de Moura while employed by Microsoft Research and now Amazon Web Services, and has had significant contributions from other coauthors and collaborators during its history. It was launched by Leonardo de Moura at Microsoft Research in 2013. The initial versions of the language, later known as Lean 1 and 2, were experimental and contained features such as support for homotopy type theory – based foundations that were later dropped. Lean 3 (first released Jan 20, 2017) was the first moderately stable version of Lean. It was implemented primarily in C++ with some features written in L ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Timothy Gowers
Sir William Timothy Gowers, (; born 20 November 1963) is a British mathematician. He is the holder of the Combinatorics chair at the Collège de France, a director of research at the University of Cambridge and a Fellow of Trinity College, Cambridge. In 1998, he received the Fields Medal for research connecting the fields of functional analysis and combinatorics. Education Gowers attended King's College School, Cambridge, as a choirboy in the choir of King's College, Cambridge, King's College choir, and then Eton College as a King's Scholar, where he was taught mathematics by Norman Routledge. In 1981, Gowers won a gold medal at the International Mathematical Olympiad with a perfect score. He completed his PhD, with a dissertation on ''Symmetric Structures in Banach Spaces'' at Trinity College, Cambridge in 1990, supervised by Béla Bollobás. Career and research After his PhD, Gowers was elected to a Junior Research Fellowship at Trinity College. From 1991 until his return to ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Additive Combinatorics
Additive combinatorics is an area of combinatorics in mathematics. One major area of study in additive combinatorics are ''inverse problems'': given the size of the sumset is small, what can we say about the structures of and ? In the case of the integers, the classical Freiman's theorem provides a partial answer to this question in terms of multi-dimensional arithmetic progressions. Another typical problem is to find a lower bound for in terms of and . This can be viewed as an inverse problem with the given information that is sufficiently small and the structural conclusion is then of the form that either or is the empty set; however, in literature, such problems are sometimes considered to be direct problems as well. Examples of this type include the Erdős–Heilbronn Conjecture (for a restricted sumset) and the Cauchy–Davenport Theorem. The methods used for tackling such questions often come from many different fields of mathematics, including combinatorics, ergod ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Katalin Marton
Katalin Marton (9 December 1941 – 13 December 2019) was a Hungarian mathematician, born in Budapest. Education and career Marton obtained her PhD from Eötvös Loránd University in 1965 and worked at the Department of Numerical Mathematics, Central Research Institute for Physics, Budapest from 1965 to 1973. Important influences on her early career were her attendance at the combinatorics seminar organised by Alfréd Rényi from 1966, meeting Roland Dobrushin in Debrecen in 1967 (which led to her visiting the Institute for Problems in Information Transmission in Moscow in 1969), and her collaboration with Imre Csiszár which began in 1972. From 1973 she worked at the Alfréd Rényi Institute of Mathematics of the Hungarian Academy of Sciences in Budapest, visiting the United States in 1977 (for the International Symposium on Information Theory in Ithaca) and in 1979–80 (meeting Robert Gallager at MIT and Robert M. Gray at Stanford). Research interests Marton worked o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kneser%27s Theorem (combinatorics)
In the branch of mathematics known as additive combinatorics, Kneser's theorem can refer to one of several related theorems regarding the sizes of certain sumsets in abelian groups. These are named after Martin Kneser, who published them in 1953 and 1956. They may be regarded as extensions of the Cauchy–Davenport theorem, which also concerns sumsets in groups but is restricted to groups whose order is a prime number. The first three statements deal with sumsets whose size (in various senses) is strictly smaller than the sum of the size of the summands. The last statement deals with the case of equality for Haar measure in connected compact abelian groups. Strict inequality If G is an abelian group and C is a subset of G , the group H(C):= \ is the ''stabilizer'' of C . Cardinality Let G be an abelian group. If A and B are nonempty finite subsets of G satisfying , A + B, < , A, + , B, and is the stabilizer of [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Solvable Group
In mathematics, more specifically in the field of group theory, a solvable group or soluble group is a group that can be constructed from abelian groups using extensions. Equivalently, a solvable group is a group whose derived series terminates in the trivial subgroup. Motivation Historically, the word "solvable" arose from Galois theory and the proof of the general unsolvability of quintic equations. Specifically, a polynomial equation is solvable in radicals if and only if the corresponding Galois group is solvable (note this theorem holds only in characteristic 0). This means associated to a polynomial f \in F /math> there is a tower of field extensionsF = F_0 \subseteq F_1 \subseteq F_2 \subseteq \cdots \subseteq F_m=Ksuch that # F_i = F_ alpha_i/math> where \alpha_i^ \in F_, so \alpha_i is a solution to the equation x^ - a where a \in F_ # F_m contains a splitting field for f(x) Example The smallest Galois field extension of \mathbb containing the elementa = \sqr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Terence Tao
Terence Chi-Shen Tao (; born 17 July 1975) is an Australian-American mathematician, Fields medalist, and professor of mathematics at the University of California, Los Angeles (UCLA), where he holds the James and Carol Collins Chair in the College of Letters and Sciences. His research includes topics in harmonic analysis, partial differential equations, algebraic combinatorics, arithmetic combinatorics, geometric combinatorics, probability theory, compressed sensing and analytic number theory. Tao was born to Chinese immigrant parents and raised in Adelaide. Tao won the Fields Medal in 2006 and won the Royal Medal and Breakthrough Prize in Mathematics in 2014, and is a 2006 MacArthur Fellow. Tao has been the author or co-author of over three hundred research papers, and is widely regarded as one of the greatest living mathematicians. Life and career Family Tao's parents are first generation immigrants from Hong Kong to Australia.'' Wen Wei Po'', Page A4, 24 August ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
