The Art of Bijective Combinatorics
The Institute of Mathematical Sciences, Chennai, India (January-March 2016-2019)
Foreword
Some lectures for a wide audience as an introduction to the Art of Bijective Combinatorics
lecture in french
D'une lettre oubliée d'Euler (1707-1783) à la combinatoire et la physique contemporaine
(from a forgotten letter of Euler (1707-1783) to modern combinatorics and combinatorial physics)
Conférence à la BNF (bibliothèque Nationale de France), Paris, 14 Mars 2007
avec Mariette Freudenthiel et Gérard Duchamp (violons) et Marcia Pig Lagos (textes)
organisée par la SMF (Société Mathématique de France) dans le cadre de la série de conférences
"Un texte, un mathématicien"
avec le concours de la BNF, France Culture, Animath et la revue "Tangente"
résumé, slides et vidéo avec une description détaillée de la vidéo sur la page Euler
(abstract, slides and video with a detailed description of the video on the page Euler)
Trees in various science
Institute colloquium, IIT Bombay, 29 January 2013
slides (pdf, 55Mo) video(?)
(similar lecture in french: trees in the stars, trees in particles of light, Nancy, 30 May 2013)
lecture in french
Des arbres dans les étoiles, des arbres dans les grains de lumière
avec Gérard DUCHAMP (violon) et la conteuse Marcia PIG LAGOS
Collection: Sciences et société, Université de Nancy, Jeudi 30 Mai 2013
slides (pdf, 59 Mo) video
(conférence analogue en anglais, IIT Bombay, 29 Janvier 2013)
abstract
Les arbres apparaissent dans toutes les parties de l'informatique. Plus généralement des structures arborescentes sont présentes dans diverses sciences : réseaux fluviaux en hydrogéologie, molécules d'ARN, structures fractales en physique...
Des paramètres sur les arbres venant de considérations d'optimisation en informatique se retrouvent dans ces structures fluviales ou biologiques.
Ces "mathématiques des arbres" apparaissent dans des recherches récentes en physique théorique,
aussi bien vers "l'infini grand" avec la structure de notre "espace temps", que vers "l'infini petit" dans notre compréhension des particules élémentaires et de la lumière. C'est le moment des contes pour pouvoir imaginer cette science en mouvement . Le titre de la conférence est sa conclusion.
The birth of a new domain: combinatorial physics
colloquium IMSc, Chennai, India, 12 february 2015
slides (pdf, 42 Mo ) video
abstract
The interaction between Combinatorics and Physics is not new: the classical combinatorial solution of the Ising model for ferromagnetism goes back to the 60's. In the last 30 years, there has been a renaissance of combinatorics, especially what is called enumerative, algebraic and bijective combinatorics. Powerful combinatorial tools have been discovered, in relation with other domains of pure mathematics, and such tools appear to be useful for theoretical physics.
With some examples I will illustrate this fruitful interaction between combinatorics and physics, giving rise to a domain which can be called "Combinatorial Physics''. A new journal is born "Combinatorics, Physics and their Interactions'' in the prestigious series of the Annales of Poincare Institute in Paris. On the front page one can read "The unfolding of new ideas in physics is often tied to the development of new combinatorial methods, and conversely some problems in combinatorics have been successfully attacked using methods inspired by statistical physics or quantum field theory".
Proofs without words: the example of the Ramanujan continued fraction
colloquium IMSc, Chennai, February 21, 2019
slides (pdf, 28 Mo)
video link to YouTube video link to bilibili
abstract:
Visual proofs of identities were common at the Greek time, such as the Pythagoras theorem. In the same spirit, with the renaissance of combinatorics, visual proofs of much deeper identities become possible. Some identities can be interpreted at the combinatorial level, and the identity is a consequence of the construction a weight preserving bijection between the objects interpreting both sides of the identity.
In this lecture, I will give an example involving the famous and classical Ramanujan continued fraction. The construction is based on the concept of "heaps of pieces",
which gives a spatial interpretation of the commutation monoids introduced by Cartier and Foata in 1969.
An introduction to enumerative and bijective combinatorics with binary trees
conference given for TESSELATE - STEMS 2021, CMI, Chennai, India, 9 January 2021 (via Zoom Internet)
abstract:
Trees and branching structures are everywhere in nature. Their mathematical abstraction leads to the notion of binary trees, a basic notion in computer science. The simple question "how many binary trees with n nodes", will give us the opportunity to travel from old and classical combinatorics to nowadays enumerative combinatorics.
Its « philosophy » can be summarized in the following:
« replacing calculus by figures and bijections, or conversely making calculus from the visual figures ».
slides_STEMS21
slides_part I (pdf, 36Mo) slides_part II (pdf 22Mo)
sides (solution to the exercises)
video link to YouTube (1h35)
more details on the special page STEMS21