Paul Erdos: the Master of Collaboration
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LINEAR ALGEBRA METHODS in COMBINATORICS László Babai
LINEAR ALGEBRA METHODS IN COMBINATORICS L´aszl´oBabai and P´eterFrankl Version 2.1∗ March 2020 ||||| ∗ Slight update of Version 2, 1992. ||||||||||||||||||||||| 1 c L´aszl´oBabai and P´eterFrankl. 1988, 1992, 2020. Preface Due perhaps to a recognition of the wide applicability of their elementary concepts and techniques, both combinatorics and linear algebra have gained increased representation in college mathematics curricula in recent decades. The combinatorial nature of the determinant expansion (and the related difficulty in teaching it) may hint at the plausibility of some link between the two areas. A more profound connection, the use of determinants in combinatorial enumeration goes back at least to the work of Kirchhoff in the middle of the 19th century on counting spanning trees in an electrical network. It is much less known, however, that quite apart from the theory of determinants, the elements of the theory of linear spaces has found striking applications to the theory of families of finite sets. With a mere knowledge of the concept of linear independence, unexpected connections can be made between algebra and combinatorics, thus greatly enhancing the impact of each subject on the student's perception of beauty and sense of coherence in mathematics. If these adjectives seem inflated, the reader is kindly invited to open the first chapter of the book, read the first page to the point where the first result is stated (\No more than 32 clubs can be formed in Oddtown"), and try to prove it before reading on. (The effect would, of course, be magnified if the title of this volume did not give away where to look for clues.) What we have said so far may suggest that the best place to present this material is a mathematics enhancement program for motivated high school students. -
The Number of Dissimilar Supergraphs of a Linear Graph
Pacific Journal of Mathematics THE NUMBER OF DISSIMILAR SUPERGRAPHS OF A LINEAR GRAPH FRANK HARARY Vol. 7, No. 1 January 1957 THE NUMBER OF DISSIMILAR SUPERGRAPHS OF A LINEAR GRAPH FRANK HARARY 1. Introduction* A (p, q) graph is one with p vertices and q lines. A formula is obtained for the number of dissimilar occurrences of a given (α, β) graph H as a subgraph of all (p, q) graphs G, oc<ip, β <: q, that is, for the number of dissimilar (p, q) supergraphs of H. The enumeration methods are those of Pόlya [7]. This result is then appli- ed to obtain formulas for the number of dissimilar complete subgraphs (cliques) and cycles among all (p, q) graphs. The formula for the num- ber of rooted graphs in [2] is a special case of the number of dissimilar cliques. This note complements [3] in which the number of dissimilar {p, k) subgraphs of a given (p, q) graph is found. We conclude with a discussion of two unsolved problems. A {linear) graph G (see [5] as a general reference) consists of a finite set V of vertices together with a prescribed subset W of the col- lection of all unordered pairs of distinct vertices. The members of W are called lines and two vertices vu v% are adjacent if {vlt v2} e W, that is, if there is a line joining them. By the complement Gr of a graph G, we mean the graph whose vertex-set coincides with that of G, in which two vertices are adjacent if and only if they are not adjacent in G. -
Remembering Frank Harary
Discrete Mathematics Letters Discrete Math. Lett. 6 (2021) 1–7 www.dmlett.com DOI: 10.47443/dml.2021.s101 Editorial Remembering Frank Harary On March 11, 2005, at a special session of the 36th Southeastern International Conference on Combinatorics, Graph The- ory, and Computing held at Florida Atlantic University in Boca Raton, the famous mathematician Ralph Stanton, known for his work in combinatorics and founder of the Institute of Combinatorics and Its Applications, stated that the three mathematicians who had the greatest impact on modern graph theory have now all passed away. Stanton was referring to Frenchman Claude Berge of France, Canadian William Tutte, originally from England, and a third mathematician, an American, who had died only 66 days earlier and to whom this special session was being dedicated. Indeed, that day, March 11, 2005, would have been his 84th birthday. This third mathematician was Frank Harary. Let’s see what led Harary to be so recognized by Stanton. Frank Harary was born in New York City on March 11, 1921. He was the oldest child of Jewish immigrants from Syria and Russia. He earned a B.A. degree from Brooklyn College in 1941, spent a graduate year at Princeton University from 1943 to 1944 in theoretical physics, earned an M.A. degree from Brooklyn College in 1945, spent a year at New York University from 1945 to 1946 in applied mathematics, and then moved to the University of California at Berkeley, where he wrote his Ph.D. Thesis on The Structure of Boolean-like Rings, in 1949, under Alfred Foster. -
Leverages and Constraints for Turkish Foreign Policy in Syrian War: a Structural Balance Approach
Instructions for authors, permissions and subscription information: E-mail: [email protected] Web: www.uidergisi.com.tr Leverages and Constraints for Turkish Foreign Policy in Syrian War: A Structural Balance Approach Serdar Ş. GÜNER* and Dilan E. KOÇ** * Assoc. Prof. Dr., Department of International Relations, Bilkent University ** Student, Department of International Relations, Bilkent University To cite this article: Güner, Serdar Ş. and Koç, Dilan E., “Leverages and Constraints for Turkish Foreign Policy in Syrian War: A Structural Balance Approach”, Uluslararası İlişkiler, Volume 15, No. 59, 2018, pp. 89-103. Copyright @ International Relations Council of Turkey (UİK-IRCT). All rights reserved. No part of this publication may be reproduced, stored, transmitted, or disseminated, in any form, or by any means, without prior written permission from UİK, to whom all requests to reproduce copyright material should be directed, in writing. References for academic and media coverages are beyond this rule. Statements and opinions expressed in Uluslararası İlişkiler are the responsibility of the authors alone unless otherwise stated and do not imply the endorsement by the other authors, the Editors and the Editorial Board as well as the International Relations Council of Turkey. Uluslararası İlişkiler Konseyi Derneği | Uluslararası İlişkiler Dergisi Web: www.uidergisi.com.tr | E- Mail: [email protected] Leverages and Constraints for Turkish Foreign Policy in Syrian War: A Structural Balance Approach Serdar Ş. GÜNER Assoc. Prof. Dr., Department of International Relations, Bilkent University, Ankara, Turkey. E-mail: [email protected] Dilan E. KOÇ Student, Department of International Relations, Bilkent University, Ankara, Turkey. E-mail: [email protected] The authors thank participants of the Seventh Eurasian Peace Science Network Meeting of 2018 and anonymous referees for their comments and suggestions. -
Introduction to Graph Theory: a Discovery Course for Undergraduates
Introduction to Graph Theory: A Discovery Course for Undergraduates James M. Benedict Augusta State University Contents 1 Introductory Concepts 1 1.1 BasicIdeas ...................................... 1 1.2 Graph Theoretic Equality . 2 1.3 DegreesofVertices .................................. 4 1.4 Subgraphs....................................... 6 1.5 The Complement of a Graph . 7 2 Special Subgraphs 9 2.1 Walks ......................................... 9 2.2 Components...................................... 10 2.3 BlocksofaGraph................................... 11 3 Three Famous Results and One Famous Graph 14 3.1 The Four-Color Theorem . 14 3.2 PlanarGraphs..................................... 16 3.3 ThePetersenGraph ................................. 18 3.4 TraceableGraphs ................................... 18 K(3;3;3) = H1 H2 Removing the edge w1v2 destroys the only C4 v 3 u1 H1: H2: w3 v v2 3 u w1 u 2 u u 2 v 1 3 w 1 w 2 2 w3 u3 w1 v2 v1 Place any edge of H1 into H2 or (vice versa) and a C4 is created. i Remarks By reading through this text one can acquire a familiarity with the elementary topics of Graph Theory and the associated (hopefully standard) notation. The notation used here follows that used by Gary Chartrand at Western Michigan University in the last third of the 20th century. His usage of notation was in‡uenced by that of Frank Harary at the University of Michigan beginning in the early 1950’s. The text’s author was Chartrand’s student at WMU from 1973 to 1976. In order to actually learn any graph theory from this text, one must work through and solve the problems found within it. Some of the problems are very easy. -
Hierarchical Self-Assembly of Telechelic Star Polymers: from Soft Patchy Particles to Gels and Diamond Crystals
Home Search Collections Journals About Contact us My IOPscience Hierarchical self-assembly of telechelic star polymers: from soft patchy particles to gels and diamond crystals This content has been downloaded from IOPscience. Please scroll down to see the full text. 2013 New J. Phys. 15 095002 (http://iopscience.iop.org/1367-2630/15/9/095002) View the table of contents for this issue, or go to the journal homepage for more Download details: IP Address: 131.130.87.134 This content was downloaded on 18/01/2017 at 13:41 Please note that terms and conditions apply. You may also be interested in: A systematic coarse-graining strategy for semi-dilute copolymer solutions: from monomersto micelles Barbara Capone, Ivan Coluzza and Jean-Pierre Hansen Polymer solutions: from hard monomers to soft polymers Jean-Pierre Hansen, Chris I Addison and Ard A Louis Computer simulations of supercooled polymer melts in the bulk and in confinedgeometry J Baschnagel and F Varnik Theoretical models for bridging timescales in polymer dynamics M G Guenza Structural properties of dendrimer–colloid mixtures Dominic A Lenz, Ronald Blaak and Christos N Likos Correlations in concentrated dendrimer solutions I O Götze and C N Likos Topological characteristics of model gels Mark A Miller, Ronald Blaak and Jean-Pierre Hansen Computer simulations of polyelectrolyte stars and brushes Christos N Likos, Ronald Blaak and Aaron Wynveen Conformational and dynamical properties of ultra-soft colloids in semi-dilute solutions under shear flow Sunil P Singh, Dmitry A Fedosov, Apratim -
Generalized Sum of Stella Octangula Numbers
DOI: 10.5281/zenodo.4662348 Generalized Sum of Stella Octangula Numbers Amelia Carolina Sparavigna Department of Applied Science and Technology, Politecnico di Torino A generalized sum is an operation that combines two elements to obtain another element, generalizing the ordinary addition. Here we discuss that concerning the Stella Octangula Numbers. We will also show that the sequence of these numbers, OEIS A007588, is linked to sequences OEIS A033431, OEIS A002378 (oblong or pronic numbers) and OEIS A003154 (star numbers). The Cardano formula is also discussed. In fact, the sequence of the positive integers can be obtained by means of Cardano formula from the sequence of Stella Octangula numbers. Keywords: Groupoid Representations, Integer Sequences, Binary Operators, Generalized Sums, OEIS, On-Line Encyclopedia of Integer Sequences, Cardano formula. Torino, 5 April 2021. A generalized sum is a binary operation that combines two elements to obtain another element. In particular, this operation acts on a set in a manner that its two domains and its codomain are the same set. Some generalized sums have been previously proposed proposed for different sets of numbers (Fibonacci, Mersenne, Fermat, q-numbers, repunits and others). The approach was inspired by the generalized sums used for entropy [1,2]. The analyses of sequences of integers and q-numbers have been collected in [3]. Let us repeat here just one of these generalized sums, that concerning the Mersenne n numbers [4]. These numbers are given by: M n=2 −1 . The generalized sum is: M m⊕M n=M m+n=M m+M n+M m M n In particular: M n⊕M 1=M n +1=M n+M 1+ M n M 1 1 DOI: 10.5281/zenodo.4662348 The generalized sum is the binary operation which is using two Mersenne numbers to have another Mersenne number. -
Notations Used 1
NOTATIONS USED 1 NOTATIONS ⎡ (n −1)(m − 2)⎤ Tm,n = n 1+ - Gonal number of rank n with sides m . ⎣⎢ 2 ⎦⎥ n(n +1) T = - Triangular number of rank n . n 2 1 Pen = (3n2 − n) - Pentagonal number of rank n . n 2 2 Hexn = 2n − n - Hexagonal number of rank n . 1 Hep = (5n2 − 3n) - Heptagonal number of rank n . n 2 2 Octn = 3n − 2n - Octagonal number of rank n . 1 Nan = (7n2 − 5n) - Nanogonal number of rank n . n 2 2 Decn = 4n − 3n - Decagonal number of rank n . 1 HD = (9n 2 − 7n) - Hendecagonal number of rank n . n 2 1 2 DDn = (10n − 8n) - Dodecagonal number of rank n . 2 1 TD = (11n2 − 9n) - Tridecagonal number of rank n . n 2 1 TED = (12n 2 −10n) - Tetra decagonal number of rank n . n 2 1 PD = (13n2 −11n) - Pentadecagonal number of rank n . n 2 1 HXD = (14n2 −12n) - Hexadecagonal number of rank n . n 2 1 HPD = (15n2 −13n) - Heptadecagonal number of rank n . n 2 NOTATIONS USED 2 1 OD = (16n 2 −14n) - Octadecagonal number of rank n . n 2 1 ND = (17n 2 −15n) - Nonadecagonal number of rank n . n 2 1 IC = (18n 2 −16n) - Icosagonal number of rank n . n 2 1 ICH = (19n2 −17n) - Icosihenagonal number of rank n . n 2 1 ID = (20n 2 −18n) - Icosidigonal number of rank n . n 2 1 IT = (21n2 −19n) - Icositriogonal number of rank n . n 2 1 ICT = (22n2 − 20n) - Icositetragonal number of rank n . n 2 1 IP = (23n 2 − 21n) - Icosipentagonal number of rank n . -
Combinatorics: a First Encounter
Combinatorics: a first encounter Darij Grinberg Thursday 10th January, 2019at 9:29pm (unfinished draft!) Contents 1. Preface1 1.1. Acknowledgments . .4 2. What is combinatorics?4 2.1. Notations and conventions . .4 1. Preface These notes (which are work in progress and will remain so for the foreseeable fu- ture) are meant as an introduction to combinatorics – the mathematical discipline that studies finite sets (roughly speaking). When finished, they will cover topics such as binomial coefficients, the principles of enumeration, permutations, parti- tions and graphs. The emphasis falls on enumerative combinatorics, meaning the art of computing sizes of finite sets (“counting”), and graph theory. I have tried to keep the presentation as self-contained and elementary as possible. The reader is assumed to be familiar with some basics such as induction proofs, equivalence relations and summation signs, as well as have some experience with mathematical proofs. One of the best places to catch up on these basics and to gain said experience is the MIT lecture notes [LeLeMe16] (particularly their first five chapters). Two other resources to familiarize oneself with proofs are [Hammac15] and [Day16]. Generally, most good books about “reading and writing mathemat- ics” or “introductions to abstract mathematics” should convey these skills, although the extent to which they actually do so may differ. These notes are accompanying two classes on combinatorics (Math 4707 and 4990) I am giving at the University of Minneapolis in Fall 2017. Here is a (subjective and somewhat random) list of recommended texts on the kinds of combinatorics that will be considered in these notes: • Enumerative combinatorics (aka counting): 1 Notes on graph theory (Thursday 10th January, 2019, 9:29pm) page 2 – The very basics of the subject can be found in [LeLeMe16, Chapters 14– 15]. -
Structural Balance: a Generalization of Heider's Theory'
VOL. 63, No. 5 SEPTEMBER, 1956 THE PSYCHOLOGICAL REVIEW STRUCTURAL BALANCE: A GENERALIZATION OF HEIDER'S THEORY' DORWIN CARTWRIGHT AND FRANK HARARY Research Center for Group Dynamics, University of Michigan A persistent problem of psychology will arise to change it toward a state has been how to deal conceptually of balance. These pressures may with patterns of interdependent prop- work to change the relation of affec- erties. This problem has been cen- tion between P and 0, the relation of tral, of course, in the theoretical responsibility between 0 and X, or the treatment by Gestalt psychologists of relation of evaluation between P phenomenal or neural configurations andX. or fields (12, 13, 15). It has also The purpose of this paper is to been of concern to social psychologists present and develop the consequences and sociologists who attempt to em- of a formal definition of balance which ploy concepts referring to social sys- is consistent with Heider's conception tems (18). and which may be employed in a more Heider (19), reflecting the general general treatment of empirical con- field-theoretical approach, has con- figurations. The definition is stated sidered certain aspects of cognitive in terms of the mathematical theory fields which contain perceived people of linear graphs (8, 14) and makes use and impersonal objects or events. of a distinction between a given rela- His analysis focuses upon what he calls tion and its opposite relation. Some the P-O-X unit of a cognitive field, of the ramifications of this definition consisting of P (one person), 0 (an- are then examined by means of other person), and X (an impersonal theorems derivable from the definition entity). -
Regular Graphs Containing a Given Graph
Regular graphs containing a given graph Autor(en): Akiyama, Jin / Era, Hiroshi / Harary, Frank Objekttyp: Article Zeitschrift: Elemente der Mathematik Band (Jahr): 38 (1983) Heft 1 PDF erstellt am: 03.10.2021 Persistenter Link: http://doi.org/10.5169/seals-37177 Nutzungsbedingungen Die ETH-Bibliothek ist Anbieterin der digitalisierten Zeitschriften. Sie besitzt keine Urheberrechte an den Inhalten der Zeitschriften. Die Rechte liegen in der Regel bei den Herausgebern. Die auf der Plattform e-periodica veröffentlichten Dokumente stehen für nicht-kommerzielle Zwecke in Lehre und Forschung sowie für die private Nutzung frei zur Verfügung. Einzelne Dateien oder Ausdrucke aus diesem Angebot können zusammen mit diesen Nutzungsbedingungen und den korrekten Herkunftsbezeichnungen weitergegeben werden. Das Veröffentlichen von Bildern in Print- und Online-Publikationen ist nur mit vorheriger Genehmigung der Rechteinhaber erlaubt. Die systematische Speicherung von Teilen des elektronischen Angebots auf anderen Servern bedarf ebenfalls des schriftlichen Einverständnisses der Rechteinhaber. Haftungsausschluss Alle Angaben erfolgen ohne Gewähr für Vollständigkeit oder Richtigkeit. Es wird keine Haftung übernommen für Schäden durch die Verwendung von Informationen aus diesem Online-Angebot oder durch das Fehlen von Informationen. Dies gilt auch für Inhalte Dritter, die über dieses Angebot zugänglich sind. Ein Dienst der ETH-Bibliothek ETH Zürich, Rämistrasse 101, 8092 Zürich, Schweiz, www.library.ethz.ch http://www.e-periodica.ch El Math Vol 38, 1983 15 Der Grundgedanke dieses Beweises ist also, zu zeigen, dass diejenigen Paare (a,b), deren Schrittzahl T(a,b) die Abschätzung von Dixon (Lemma 2) erfüllen, den Hauptbeitrag zu dem gesuchten Mittelwert liefern. Zum Abschluss seien noch einige numerische Ergebnisse angegeben, wie man sie mit einem programmierbaren Taschenrechner errechnen kann. -
Embedding Graphs Into Larger Graphs: Results, Methods, and Problems
Embedding graphs into larger graphs: results, methods, and problems Mikl´os Simonovits and Endre Szemer´edi Alfr´ed R´enyi Institute of Mathematics, Hungarian Academy of Sciences, email: [email protected], [email protected] arXiv:1912.02068v1 [math.CO] 4 Dec 2019 2 Mikl´os Simonovits and Endre Szemer´edi: March29, 2019 Contents 1 Introduction.............................. 6 2 Thebeginnings............................ 9 2.1 Veryearlyresults....................... 9 2.2 Constructions......................... 13 2.3 Somehistoricalremarks . .. .. .. .. .. .. .. 13 2.4 Earlyresults ......................... 14 2.5 WhichUniverse? ....................... 16 2.6 Ramseyordensity? ..................... 21 2.7 Whyaretheextremalproblemsinteresting? . 22 2.8 Ramsey Theory and the birth of the Random Graph Method 23 2.9 Dichotomy, randomness and matrix graphs . 24 2.10 Ramsey problems similar to extremal problems . 25 2.11 Applications in Continuous Mathematics . 26 2.12 TheStabilitymethod .................... 26 2.13 The“typicalstructure” . 29 2.14 SupersaturatedGraphs . 31 2.15 Lov´asz-Simonovits Stability theorem . 32 2.16 Degeneratevs Non-degenerateproblems . 33 2.17 Diractheorem:introduction. 36 2.18 Equitable Partition . 36 2.19 Packing, Covering, Tiling, L-factors ............ 37 3 “Classicalmethods” ......................... 40 3.1 DetourI:Induction? ..................... 40 3.2 Detour II: Applications of Linear Algebra . 41 4 Methods: Randomness and the Semi-random method . 43 4.1 Various ways to use randomness in Extremal Graph Theory 44 4.2 Thesemi-randommethod . 45 4.3 Independentsetsinuncrowdedgraphs . 45 4.4 Uncrowdedhypergraphs . 47 4.5 Ramseyestimates ...................... 48 4.6 InfiniteSidonsequences . .. .. .. .. .. .. .. 49 4.7 The Heilbronn problem, old results . 50 4.8 Generalizations of Heilbronn’s problem, new results . 50 4.9 TheHeilbronnproblem,anupperbound. 51 4.10 TheGowersproblem..................... 51 3 4 Mikl´os Simonovits and Endre Szemer´edi: March29, 2019 4.11 Pippenger-Spencertheorem .