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At least 235 records · Page 13Linked to original sources
arXiv2009

Roots of a compact Lie group

This expository article introduces the topic of roots in a compact Lie group. Compared to the many other treatments of this standard topic, I intended for mine to be relatively elementary, example-driven, and free of unnecessary abstractions. Some familiarity with matrix groups and with maximal tori is assumed. This article is self-contained, but is also intended to serve as a supplemental 10th chapter of an eventual new edition of my textbook, ``Matrix Groups for Undergraduates.''

math.DG↗
arXiv2009

Two-player envy-free multi-cake division

We introduce a generalized cake-cutting problem in which we seek to divide multiple cakes so that two players may get their most-preferred piece selections: a choice of one piece from each cake, allowing for the possibility of linked preferences over the cakes. For two players, we show that disjoint envy-free piece selections may not exist for two cakes cut into two pieces each, and they may not exist for three cakes cut into three pieces each. However, there do exist such divisions for two cakes cut into three pieces each, and for three cakes cut into four pieces each. The resulting allocations of pieces to players are Pareto-optimal with respect to the division. We use a generalization of Sperner's lemma on the polytope of divisions to locate solutions to our generalized cake-cutting problem.

math.CO↗
arXiv2009

N-person envy-free chore division

In contrast to the classical cake-cutting problem (how to fairly divide a desirable object), "chore division" is the problem of how to divide an undesirable object. We develop the first explicit algorithm for envy-free chore division among N people, a counterpart to the N-person envy-free cake-division solution of Brams-Taylor (1995). This is accomplished by exploiting a notion of "irrevocable advantage" for chores. We discuss the differences between cake-cutting and chore division and additional problems encountered in chore division.

math.CO↗
arXiv2009

From Goeritz matrices to quasi-alternating links

Knot Theory is currently a very broad field. Even a long survey can only cover a narrow area. Here we concentrate on the path from Goeritz matrices to quasi-alternating links. On the way, we often stray from the main road and tell related stories, especially if they allow as to place the main topic in a historical context. For example, we mention that the Goeritz matrix was preceded by the Kirchhoff matrix of an electrical network. The network complexity extracted from the matrix corresponds to the determinant of a link. We assume basic knowledge of knot theory and graph theory, however, we offer a short introduction under the guise of a historical perspective. Chapter IV of the book "KNOTS: From combinatorics of knot diagrams to combinatorial topology based on knots will be based on this survey,

math.GT↗
arXiv2009

Transseries: Composition, Recursion, and Convergence

Additional remarks and questions for transseries. In particular: properties of composition for transseries; the recursive nature of the construction of R[[[ x ]]]; modes of convergence for transseries. There are, at this stage, questions and missing proofs in the development.

math.RA↗
arXiv2009

Transseries: Ratios, Grids, and Witnesses

More remarks and questions on transseries. In particular we deal with the system of ratio sets and grids used in the grid-based formulation of transseries. This involves a "witness" concept that keeps track of the ratios required for each computation. There are, at this stage, questions and missing proofs in the development.

math.RA↗
arXiv2009

(Non-)amenability of B(E)

In 1972, the late B. E. Johnson introduced the notion of an amenable Banach algebra and asked whether the Banach algebra $B(E)$ of all bounded linear operators on a Banach space $E$ could ever be amenable if $\dim E = \infty$. Somewhat surprisingly, this question was answered positively only very recently as a by-product of the Argyros--Haydon result that solves the "scalar plus compact problem": there is an infinite-dimensional Banach space $E$, the dual of which is $\ell^1$, such that $B(E) = K(E)+ \mathbb{C} \id_E$. Still, $B(\ell^2)$ is not amenable, and in the past decade, $ B(\ell^p)$ was found to be non-amenable for $p=1,2,\infty$ thanks to the work of C. J. Read, G. Pisier, and N. Ozawa. We survey those results, and then--based on joint work with M. Daws--outline a proof that establishes the non-amenability of $B(\ell^p)$ for all $p \in [1,\infty]$.

math.FA↗
arXiv2009

A derivation of Benford's Law ... and a vindication of Newcomb

We show how Benford's Law (BL) for first, second, ..., digits, emerges from the distribution of digits of numbers of the type $a^{R}$, with $a$ any real positive number and $R$ a set of real numbers uniformly distributed in an interval $[ P\log_a 10, (P +1) \log_a 10) $ for any integer $P$. The result is shown to be number base and scale invariant. A rule based on the mantissas of the logarithms allows for a determination of whether a set of numbers obeys BL or not. We show that BL applies to numbers obtained from the {\it multiplication} or {\it division} of numbers drawn from any distribution. We also argue that (most of) the real-life sets that obey BL are because they are obtained from such basic arithmetic operations. We exhibit that all these arguments were discussed in the original paper by Simon Newcomb in 1881, where he presented Benford's Law.

math.PR↗
arXiv2010

An invitation to model-theoretic Galois theory

We carry out some of Galois's work in the setting of an arbitrary first-order theory T. We replace the ambient algebraically closed field by a large model M of T, replace fields by definably closed subsets of M, assume that T codes finite sets, and obtain the fundamental duality of Galois theory matching subgroups of the Galois group of L over F with intermediate extensions. This exposition of a special case of Poizat's "Une théorie de Galois imaginaire." (1983) has the advantage of requiring almost no background beyond familiarity with fields, polynomials, first-order formulae, and automorphisms.

math.LO↗
arXiv2018

Irrationality From The Book

We generalize Tennenbaum's geometric proof of the irrationality of sqrt(2) to sqrt(n) for n = 3, 5, 6 and 10. Modified version published in Mathematics Magazine \textbf{85} (2012), no. 2, 110--114.

math.HO↗
arXiv2009

Gold ratio and a trigonometric identity

We give two proofs of the identity $$\sqrt{\frac{\cos\frac{2π}{5}} {\cos\fracπ{5}}}+\sqrt{\frac{\cos\fracπ{5}} {\cos\frac{2π}{5}} }=\sqrt{5},$$ using and not using the gold ratio.

math.HO↗
arXiv2009

A Tasty Combination: Multivariable Calculus and Differential Forms

Differential Calculus is a staple of the college mathematics major's diet. Eventually one becomes tired of the same routine, and wishes for a more diverse meal. The college math major may seek to generalize applications of the derivative that involve functions of more than one variable, and thus enjoy a course on Multivariate Calculus. We serve this article as a culinary guide to differentiating and integrating functions of more than one variable -- using differential forms which are the basis for de Rham Cohomology.

math.DG↗
arXiv2009

The concept of primes and the algorithm for counting the greatest common divisor in Ancient China

When people mention the number theoretical achievements in Ancient China, the famous Chinese Remainder Theorem always springs to mind. But, two more of them--the concept of primes and the algorithm for counting the greatest common divisor, are rarely spoken. Some scholars even think that Ancient China has not the concept of primes. The aim of this paper is to show that the concept of primes in Ancient China can be traced back to the time of Confuciusor (about 500 B.C.) or more ago. This implies that the concept of primes in Ancient China is much earlier than the concept of primes in Euclid's \emph{Elements}(about 300 B.C.) of Ancient Greece. We also shows that the algorithm for counting the greatest common divisor in Ancient China is essentially the Euclidean algorithm or the binary gcd algorithm. Donald E. Knuth said that "the binary gcd algorithm was discovered by J. Stein in 1961". Nevertheless, Knuth was wrong. The ancient Chinese algorithm is clearly much earlier than J. Stein's algorithm.

math.HO↗
arXiv2009

A cornucopia of pythagorean triangles

Consider two circles, externally tangential,and with integer radii R1, R2; and with R1>R2.The two circles have three tangent lines in common, one of them being T1T2. If M is the midpoint of T1T2, and K the point of intersection of the lines C1C2 and T1T2;then 16 right triangles are formed(C1 and C2 are the two circle centers), see Figure 1.In Section 6 of this paper, we find the precice form the two integers R1 and R2 must have, in order that the sixteen aforementioned right triangles be Pythagorean.

math.HO↗
arXiv2009

Aronszajn's Criterion for Euclidean Space

We give a simple proof of a characterization of euclidean space due to Aronszajn and derive a well-known characterization due to Jordan & von Neumann as a corollary.

math.HO↗