# Combinatorics

The main focus of this activity is the interrelation between algebraic structure and algorithms. We plan to work on the following subjects:

- Algebraic structures (Combinatorial Hopf Algebras, Operads, Monoids, ...) related to algorithms;
- Enumerative combinatorics and symbolic dynamic.
- Object oriented software design for modeling mathematics and development of SageMath;

More precisely, the research project takes place in effective algebraic combinatorics, at the interface of enumerative combinatorics and analysis of algorithms on one hand and symbolic and algebraic computation on the other hand. The objective is twofold: firstly, thanks to vast generalization of the notion of generating series, we hope to give a theoretical framework allowing to study the fine behavior of various algorithms. Reciprocally, the study of those very same algorithms gives a new mean to discover algebraic identities. Those identities have many applications in mathematics, in particular in representation theory but also in physics (mainly statistical physics).

The research relies deeply on computer experimentation and contains as a consequence an important software development part within the Sage-Combinat software project. However, the required level of sophistication, flexibility, and breath of computational tools is reaching a point where large scale collaborative development is critical. The design and collaborative development of such a software is raising research-grade computer science challenges around the modelling of mathematics, the management of large hierarchy of (object oriented) classes, etc.

Those very specific questions also raise more general combinatorial questions. We therefore plan to work on enumerative combinatorics and cellular automaton, in particular on trees. This activity is conducted with close collaborators in France, Germany, North America, and India.

## High Performance Combinatorics

partly joint with Jean Fromentin In this talk, I will report on several experiments around large scale enumerations in enumerative and algebraic combinatorics. In a first part, I'll present a small framework implemented in Sagemath allowing to perform map/reduce like computations on large recursively defined sets. Though it ...

## Polytopal Realizations of Finite Type g-Vector Fans

To any cluster algebra with principal coefficients A, and by extension to any other cluster algebra, it is associated a simplicial fan that encodes the underlying combinatorial structure: the g-vector fan. When A is of finite type, this fan has a natural interpretation in terms of a (not necessarily finite ...

## Limite d'échelle des permutations séparables : description et universalité du permuton séparable Brownien

Travaux en collaboration avec F. Bassino, M. Bouvel, V. Feray, L. Gerin et A. Pierrot. Le permuton séparable Brownien a été introduit par Bassino et. al. (2016) comme la limite d'échelle des permutations séparables. C'est une mesure aléatoire sur le carré unité, construite à partir d'une excursion ...

Translations: fr