This talk will cover two recent advancements in the theory of online algorithms for dynamic matching markets. The first set of results concern a stochastic model of matching with Poisson arrivals and memoryless departures over edge-weighted graphs. The second set of results focus on the incorporation of serial correlation properties in classical online stochastic matching models. We develop new mathematical programming relaxations and correlated rounding schemes, yielding the first constant-factor performance guarantees in such settings.[-]

We study repeated bilateral trade where an adaptive σ-smooth adversary generates the valuations of sellers and buyers. We provide a complete characterization of the regret regimes for fixed-price mechanisms under different feedback models in the two cases where the learner can post either the same or different prices to buyers and sellers. We begin by showing that the minimax regret after $T$ rounds is of order $\sqrt{T}$ in the full-feedback scenario. Under partial feedback, any algorithm that has to post the same price to buyers and sellers suffers worst-case linear regret. However, when the learner can post two different prices at each round, we design an algorithm enjoying regret of order $T^{3/4}$ ignoring log factors. We prove that this rate is optimal by presenting a surprising $T^{3/4}$ lower bound, which is the main technical contribution of the paper.[-]

Benoît Mandelbrot and Marcel-Paul Schützenberger first met at the Institut Poincaré in Paris in the 1950s, when both were working on topics in the then novel field of information theory. Their paths crossed again at the other end of the Atlantic on the East Coast where they were drawn into discussions on formal models of language. This was an important topic in the U.S. because these models could be useful for automatic translation, and for automatic coding of information and of programs for digital computers. In the late 1950s, a vivid debate raged whether probabilistic models or rather grammatical or rule-based models were appropriate for describing (natural) language, with notably Noam Chomsky and his students attacking the probabilistic approach. As Mandelbrot arrived in the U.S., the probabilistic model of language he had developed in his PhD became part of the discussion. Also Schützenberger got involved in the debate with his early work on coding theory. Eventually, Chomsky's arguments against probabilistic models would prevail. As a result, Mandelbrot's research went into a slightly different direction that would bring him to fractal geometry, whereas Schützenberger, via his frequent visits to the U.S., became one of the architects of the mathematics behind formal languages and coding theory.[-]

Walnut is computer software, written in Java, that implements an algorithm to decide the truth of first-order logic statements in an extension of Presburger arithmetic known as Buchi arithmetic. It can be used to prove a wide variety of results in combinatorics on words and number theory. In this course we will give an introduction to the theory behind Walnut, examples of the types of results that can be proved with it, and exercises for participants to get some hands-on training on how to use Walnut.[-]

This tutorial surveys computational aspects of cellular automata, a discrete dynamical model introduced by S. Ulam and J. von Neumann in the late 40s: a regular grid of finite state cells evolving synchronously according to a common local rule described by a finite automaton.

Formally, a cellular automaton is a tuple $(d, S, N, f)$ where $d \in \mathbb{N}$ is the dimension of the cellular space, $S$ is the finite set of states, $N \subseteq_{\text {finite }} \mathbb{Z}^d$ is the finite neighborhood and $f: S^N \rightarrow S$ is the local rule of the cellular automaton.

A configuration $c \in S^{\mathbb{Z}^d}$ is a coloring of the cellular space by states.

The global transition function $G: S^{\mathbb{Z}^d} \rightarrow S^{\mathbb{Z}^d}$ applies $f$ uniformly according to $N$, i.e. for every configuration $c \in S^{\mathbb{Z}^d}$ and every position $z \in \mathbb{Z}^d$ it holds
$$G(c)(z)=f\left(c\left(z+v_1\right), \ldots, c\left(z+v_m\right)\right) \quad \text { where } N=\left\{v_1, \ldots, v_m\right\} .$$
A space-time diagram $\Delta \in S^{\mathbb{Z}^d \times \mathbb{N}}$ is obtained by piling successive configurations of an orbit, i.e. for every time step $t \in \mathbb{N}$ it holds $\Delta_{t+1}=G\left(\Delta_t\right)$.

Computing inside the cellular space: The first part of the tutorial considers cellular automata as a universal model of computation. Several notions of universality are discussed: boolean circuit simulation, Turing universality, intrinsic universality. Special abilities of cellular automata as a model of massive parallelism are then investigated.

Computing properties of cellular automata: The second part of the tutorial considers properties of cellular automata and their computation. De Bruijn diagrams and associated regular languages are introduced as tools to decide injectivity and surjectivity of the global transition function in the one-dimensional case. Both immediate and dynamical properties are introduced, in particular the notion of limit set.

Computation and reduction: undecidability results: The last part of the tutorial considers computing by reduction to establish undecidability results on some properties of cellular automata: injectivity and surjectivity of the global transition function in higher dimensions, nilpotency and intrinsic universality in every dimension, a Rice's theorem for limit sets.[-]

Walnut is computer software, written in Java, that implements an algorithm to decide the truth of first-order logic statements in an extension of Presburger arithmetic known as Buchi arithmetic. It can be used to prove a wide variety of results in combinatorics on words and number theory. In this course we will give an introduction to the theory behind Walnut, examples of the types of results that can be proved with it, and exercises for participants to get some hands-on training on how to use Walnut.[-]

This tutorial surveys computational aspects of cellular automata, a discrete dynamical model introduced by S. Ulam and J. von Neumann in the late 40s: a regular grid of finite state cells evolving synchronously according to a common local rule described by a finite automaton.

Formally, a cellular automaton is a tuple $(d, S, N, f)$ where $d \in \mathbb{N}$ is the dimension of the cellular space, $S$ is the finite set of states, $N \subseteq_{\text {finite }} \mathbb{Z}^d$ is the finite neighborhood and $f: S^N \rightarrow S$ is the local rule of the cellular automaton.

A configuration $c \in S^{\mathbb{Z}^d}$ is a coloring of the cellular space by states.

The global transition function $G: S^{\mathbb{Z}^d} \rightarrow S^{\mathbb{Z}^d}$ applies $f$ uniformly according to $N$, i.e. for every configuration $c \in S^{\mathbb{Z}^d}$ and every position $z \in \mathbb{Z}^d$ it holds
$$G(c)(z)=f\left(c\left(z+v_1\right), \ldots, c\left(z+v_m\right)\right) \quad \text { where } N=\left\{v_1, \ldots, v_m\right\} .$$
A space-time diagram $\Delta \in S^{\mathbb{Z}^d \times \mathbb{N}}$ is obtained by piling successive configurations of an orbit, i.e. for every time step $t \in \mathbb{N}$ it holds $\Delta_{t+1}=G\left(\Delta_t\right)$.

Computing inside the cellular space: The first part of the tutorial considers cellular automata as a universal model of computation. Several notions of universality are discussed: boolean circuit simulation, Turing universality, intrinsic universality. Special abilities of cellular automata as a model of massive parallelism are then investigated.

Computing properties of cellular automata: The second part of the tutorial considers properties of cellular automata and their computation. De Bruijn diagrams and associated regular languages are introduced as tools to decide injectivity and surjectivity of the global transition function in the one-dimensional case. Both immediate and dynamical properties are introduced, in particular the notion of limit set.

Computation and reduction: undecidability results: The last part of the tutorial considers computing by reduction to establish undecidability results on some properties of cellular automata: injectivity and surjectivity of the global transition function in higher dimensions, nilpotency and intrinsic universality in every dimension, a Rice's theorem for limit sets.[-]