arXiv subjects

Davide Sclosa

Publications and source records attributed to Davide Sclosa.

10 recordsLinked to original sources

arXiv2025

If you are the smartest person in the room, you are in the wrong room

If taken seriously, the advice in the title leads to interesting combinatorics. Consider $N$ people moving between $M$ rooms as follows: at each step, simultaneously, the smartest person in each room moves to a different room of their choice, while no one else moves. The process repeats. In this paper we determine which configurations are reachable, from which other configurations, and provide bounds on the number of moves. Namely, let $G(N,M)$ be the directed graph with vertices representing all $M^N$ configurations and edges representing possible moves. We prove that the graph $G(N,M)$ is weakly connected, and that it is strongly connected if and only if $M\geq N+1$ (one extra room for maneuvering is both required and sufficient). For $M\leq N$, we show that the graph has a giant strongly connected component with $Θ(M^N)$ vertices and diameter $\mathcal O(N^2)$.

math.CO↗

arXiv2024

A Random-Walk Concentration Principle for Occupancy Processes on Finite Graphs

This paper concerns discrete-time occupancy processes on a finite graph. Our results can be formulated in two theorems, which are stated for vertex processes, but also applied to edge process (e.g., dynamic random graphs). The first theorem shows that concentration of local state averages is controlled by a random walk on the graph. The second theorem concerns concentration of polynomials of the vertex states. For dynamic random graphs, this allows to estimate deviations of edge density, triangle density, and more general subgraph densities. Our results only require Lipschitz continuity and hold for both dense and sparse graphs.

math.PR↗

arXiv2024

Dimension Bounds for Systems of Equations with Graph Structure

We introduce a broad class of equations that are described by a graph, which includes many well-studied systems. For these, we show that the number of solutions (or the dimension of the solution set) can be bounded by studying certain induced subgraphs. As corollaries, we obtain novel bounds in spectral graph theory on the multiplicities of graph eigenvalues, and in nonlinear dynamical system on the dimension of the equilibrium set of a network.

math.CO↗

arXiv2024

From Combinatorics to Geometry: The Dynamics of Graph Gradient Diffusion

We discuss a link between graph theory and geometry that arises when considering graph dynamical systems with odd interactions. The equilibrium set in such systems is not a collection of isolated points, but rather a union of manifolds, which may intersect creating singularities and may vary in dimension. We prove that geometry and stability of such manifolds are governed by combinatorial properties of the underlying graph. In particular, we derive an upper bound on the dimension of the equilibrium set using graph homology and a lower bound using graph coverings. Moreover, we show how graph automorphisms relate to geometric singularities and prove that the decomposition of a graph into $2$-vertex-connected components induces a decomposition of the equilibrium set that preserves three notions of stability.

math.DS↗

arXiv2024

Dynamical Systems on Graph Limits and Their Symmetries

The collective dynamics of interacting dynamical units on a network crucially depends on the properties of the network structure. Rather than considering large but finite graphs to capture the network, one often resorts to graph limits and the dynamics thereon. We elucidate the symmetry properties of dynamical systems on graph limits -- including graphons and graphops -- and analyze how the symmetry shape the dynamics, for example through invariant subspaces. In addition to traditional symmetries, dynamics on graph limits can support generalized noninvertible symmetries. Moreover, as asymmetric networks can have symmetric limits, we note that one can expect to see ghosts of symmetries in the dynamics of large asymmetric networks.

math.DS↗

arXiv2024

Bounded Power Series on the Real Line

We investigate power series that converge to a bounded function on the real line. First, we establish relations between coefficients of a power series and boundedness of the resulting function; in particular, we show that boundedness can be prevented by certain Turán inequalities and, in the case of real coefficients, by certain sign patterns. Second, we show that the set of bounded power series naturally supports three topologies and that these topologies are inequivalent and incomplete. In each case, we determine the topological completion. Third, we study the algebra of bounded power series, revealing the key role of the backward shift operator.

math.CA↗

arXiv2023

Completely Degenerate Equilibria of the Kuramoto Model on Networks

Kuramoto Networks contain non-hyperbolic equilibria whose stability is sometimes difficult to determine. We consider the extreme case in which all Jacobian eigenvalues are zero. In this case linearizing the system at the equilibrium leads to a Jacobian matrix which is zero in every entry. We call these equilibria completely degenerate. We prove that they exist for certain intrinsic frequencies if and only if the underlying graph is bipartite, and that they do not exist for generic intrinsic frequencies. In the case of zero intrinsic frequencies, we prove that they exist if and only if the graph has an Euler circuit such that the number of steps between any two visits at the same vertex is a multiple of 4. The simplest example is the cycle graph with 4 vertices. We prove that graphs with this property exist for every number of vertices N larger than 5 and that they become asymptotically rare for N large. Regarding stability, we prove that for any choice of intrinsic frequencies, any coupling strength and any graph with at least one edge, completely degenerate equilibria are not Lyapunov stable. As a corollary, we obtain that stable equilibria in Kuramoto Networks must have at least one strictly negative eigenvalue.

math.DS↗

arXiv2022

Algebraic Groups over Finite Fields: Connections Between Subgroups and Isogenies

Let G be a linear algebraic group defined over a finite field F_q. We present several connections between the isogenies of G and the finite groups of rational points G(F_q^n). We show that an isogeny from G' to G over F_q gives rise to a subgroup of fixed index in G(F_q^n) for infinitely many n. Conversely, we show that if G is reductive the existence of a subgroup of fixed index k for infinitely many n implies the existence of an isogeny of order k. In particular, we show that every infinite sequence of subgroups is controlled by a finite number of isogenies. This result applies to classical groups GLm, SLm, SOm, SUm, Sp2m and can be extended to non-reductive groups if k is prime to the characteristic. As a special case, we see that if G is simply connected the minimal indexes of proper subgroups of G(F_q^n) diverge to infinity. Similar results are investigated regarding the sequence G(F_p) by varying the characteristic p.

math.GR↗

arXiv2022

Kuramoto Networks with Infinitely Many Stable Equilibria

We prove that the Kuramoto model on a graph can contain infinitely many non-equivalent stable equilibria. More precisely, we prove that for every positive integer d there is a connected graph such that the set of stable equilibria contains a manifold of dimension d. In particular, we solve a conjecture of R. Delabays, T. Coletta and P. Jacquod about the number of equilibria on planar graphs. Our results are based on the analysis of balanced configurations, which correspond to equilateral polygon linkages in topology. In order to analyze the stability of manifolds of equilibria we apply topological bifurcation theory.

math.DS↗

arXiv2021

The finiteness conjecture holds in SL(2,Z>=0)^2

Let A,B be matrices in SL(2,R) having trace greater than or equal to 2. Assume the pair A,B is coherently oriented, that is, can be conjugated to a pair having nonnegative entries. Assume also that either A,B^(-1) is coherently oriented as well, or A,B have integer entries. Then the Lagarias-Wang finiteness conjecture holds for the set {A,B}, with optimal product in {A,B,AB,A^2B,AB^2}. In particular, it holds for every matrix pair in SL(2,Z>=0).

math.DS↗