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We show that the number of independent sets in an N-vertex, d-regular graph is at most (2^{d+1} - 1)^{N/2d}, where the bound is sharp for a disjoint union of complete d-regular bipartite graphs. This settles a conjecture of Alon in 1991 and…

Combinatorics · Mathematics 2015-10-26 Yufei Zhao

We give explicit formulas for the asymptotic Betti numbers, over an arbitrary field, of the ordered configuration spaces of a graph. In characteristic zero, we further give explicit formulas for the asymptotic multiplicities in homology of…

Algebraic Topology · Mathematics 2025-10-02 Louis Hainaut , Ben Knudsen , Nicholas Wawrykow

Amongst $d$-regular $r$-uniform hypergraphs on $n$ vertices, which ones have the largest number of independent sets? While the analogous problem for graphs (originally raised by Granville) is now well-understood, it is not even clear what…

Combinatorics · Mathematics 2020-02-25 Jozsef Balogh , Bela Bollobas , Bhargav Narayanan

The number of independent sets in regular bipartite expander graphs can be efficiently approximated by expressing it as the partition function of a suitable polymer model and truncating its cluster expansion. While this approach has been…

Combinatorics · Mathematics 2024-12-20 Patrick Arras , Frederik Garbe , Felix Joos

The task of this survey is to present various results on intersection patterns of convex sets. One of main tools for studying intersection patterns is a point of view via simplicial complexes. We recall the definitions of so called…

Combinatorics · Mathematics 2011-10-25 Martin Tancer

Let d=(d_1,d_2,..., d_n) be a vector of non-negative integers. We study the number of symmetric 0-1 matrices whose row sum vector equals d. While previous work has focussed on the case of zero diagonal, we allow diagonal entries to equal 1.…

Combinatorics · Mathematics 2012-03-12 Brendan D. McKay , Catherine Greenhill

We consider unitary graphs attached to Z_d^n using an analogue of the Euclidean distance. These graphs are shown to be integral when n is odd or the dimension d is even.

Combinatorics · Mathematics 2008-07-17 Si Li , Le Anh Vinh

We derive limiting distributions of symmetrized estimators of scatter, where instead of all $n(n-1)/2$ pairs of the $n$ observations we only consider $nd$ suitably chosen pairs, $1 \le d < \lfloor n/2\rfloor$. It turns out that the…

Statistics Theory · Mathematics 2023-08-21 Lutz Duembgen , Klaus Nordhausen

Let P_{n,d,D} denote the graph taken uniformly at random from the set of all labelled planar graphs on {1,2,...,n} with minimum degree at least d(n) and maximum degree at most D(n). We use counting arguments to investigate the probability…

Combinatorics · Mathematics 2011-01-28 Chris Dowden

Function graphs are graphs representable by intersections of continuous real-valued functions on the interval [0,1] and are known to be exactly the complements of comparability graphs. As such they are recognizable in polynomial time.…

Data Structures and Algorithms · Computer Science 2012-05-01 Pavel Klavík , Jan Kratochvíl , Tomasz Krawczyk , Bartosz Walczak

It is known that polytopes with at most two nonsimple vertices are reconstructible from their graphs, and that $d$-polytopes with at most $d-2$ nonsimple vertices are reconstructible from their 2-skeletons. Here we close the gap between 2…

Combinatorics · Mathematics 2018-11-28 Guillermo Pineda-Villavicencio , Julien Ugon , David Yost

The persistence diagram (PD) is an increasingly popular topological descriptor. By encoding the size and prominence of topological features at varying scales, the PD provides important geometric and topological information about a space.…

Let $k\ge 1$ be an integer. We prove that a suitable asymptotic formula for the average number of representations of integers $n=p_{1}^{k}+p_{2}^{2}+p_{3}^{2}$, where $p_1,p_2,p_3$ are prime numbers, holds in intervals shorter than the ones…

Number Theory · Mathematics 2021-06-04 Alessandro Languasco , Alessandro Zaccagnini

We consider random graphs sampled uniformly from a structured class of graphs, such as the class of graphs embeddable in a given surface. We sharpen and extend earlier results on pendant appearances, concerning for example numbers of…

Combinatorics · Mathematics 2024-05-07 Colin McDiarmid

I compute several terms of the asymptotic expansion of the number of connected labelled graphs with n nodes and m edges, for small k=m-n.

Discrete Mathematics · Computer Science 2011-03-14 Keith Briggs

Let Y be a random d-dimensional subcomplex of the (n-1)-dimensional simplex S obtained by starting with the full (d-1)-dimensional skeleton of S and then adding each d-simplex independently with probability p=c/n. We compute an explicit…

Combinatorics · Mathematics 2011-08-04 L. Aronshtam , N. Linial , T. Luczak , R. Meshulam

Multiple interval graphs are a well-known generalization of interval graphs introduced in the 1970s to deal with situations arising naturally in scheduling and allocation. A $d$-interval is the union of $d$ intervals on the real line, and a…

Computational Complexity · Computer Science 2023-09-22 Virginia Ardévol Martínez , Romeo Rizzi , Florian Sikora , Stéphane Vialette

We develop a theory of limits for sequences of dense abstract simplicial complexes, where a sequence is considered convergent if its homomorphism densities converge. The limiting objects are represented by stacks of measurable [0,1]-valued…

Combinatorics · Mathematics 2022-07-19 T. Mitchell Roddenberry , Santiago Segarra

Word-representable graphs are a subset of graphs that may be represented by a word $w$ over an alphabet composed of the vertices in the graph. In such graphs, an edge exists if and only if the occurrences of the corresponding vertices…

Data Structures and Algorithms · Computer Science 2025-02-12 Duncan Adamson

We enumerate the connected graphs that contain a number of edges growing linearly with respect to the number of vertices. So far, only the first term of the asymptotics and a bound on the error were known. Using analytic combinatorics, ie…

Combinatorics · Mathematics 2018-10-12 Elie de Panafieu