bluuebunny/crossref_metadata_2025_split huggingface dataset:
Pattern-Avoidance in Binary Fillings of Grid Shapes (short version)
Authors: Spiridonov Alexey 
Published: August 2021

A $\textit{grid shape}$ is a set of boxes chosen from a square grid; any Young diagram is an example. This paper considers a notion of pattern-avoidance for $0-1$ fillings of grid shapes, which generalizes permutation pattern-avoidance. A filling avoids some patterns if none of its sub-shapes equal any of the patterns. We focus on patterns that are $\textit{pairs}$ of $2 \times 2$ fillings. For some shapes, fillings that avoid specific $2 \times 2$ pairs are in bijection with totally nonnegative Grassmann cells, or with acyclic orientations of bipartite graphs. We prove a number of results analogous to Wilf-equivalence for these objects ―- that is, we show that for certain classes of shapes, some pattern-avoiding fillings are equinumerous with others.
Une $\textit{forme de grille}$ est un ensemble de cases choisies dans une grille carrée; un diagramme de Young en est un exemple. Cet article considère une notion de motif exclu pour un remplissage d'une forme de grille par des $0$ et des $1$, qui généralise la notion correspondante pour les permutations. Un remplissage évite certains motifs si aucune de ses sous-formes n'est égale à un motif. Nous nous concentrons sur les motifs qui sont des $\textit{paires de remplissages}$ de taille $2 \times 2$. Pour certaines formes, les remplissages évitant certaines paires de taille $2 \times 2$ sont en bijection avec les cellules de Grassmann totalement positives, ou bien avec les orientations acycliques de graphes bipartis. Nous démontrons plusieurs résultats analogues à l'équivalence de Wilf pour ces objets ―- c'est-à-dire, nous montrons que, pour certaines classes de formes, des remplissages évitant un motif donné sont en nombre égal à d'autres remplissages.
The Rees product of the cubical lattice with the chain
Authors: Muldoon Patricia , Readdy Margaret A. 
Published: August 2021

We study enumerative and homological properties of the Rees product of the cubical lattice with the chain. We give several explicit formulas for the Möbius function. The last formula is expressed in terms of the permanent of a matrix and is given by a bijective proof.
Nous étudions des propriétés énumératives et homologiques du produit de Rees du treillis cubique avec la chaîne. Nous donnons plusieurs formules explicites de la fonction de Möbius de ce poset. La dernière de ces formules est exprimée en termes du permanent d’une matrice et le résultat est donné par une preuve bijective.
Hecke group algebras as degenerate affine Hecke algebras
Authors: Hivert Florent , Schilling Anne , Thiéry Nicolas M. 
Published: August 2021

The Hecke group algebra $\operatorname{H} \mathring{W}$ of a finite Coxeter group $\mathring{W}$, as introduced by the first and last author, is obtained from $\mathring{W}$ by gluing appropriately its $0$-Hecke algebra and its group algebra. In this paper, we give an equivalent alternative construction in the case when $\mathring{W}$ is the classical Weyl group associated to an affine Weyl group $W$. Namely, we prove that, for $q$ not a root of unity, $\operatorname{H} \mathring{W}$ is the natural quotient of the affine Hecke algebra $\operatorname{H}(W)(q)$ through its level $0$ representation. The proof relies on the following core combinatorial result: at level $0$ the $0$-Hecke algebra acts transitively on $\mathring{W}$. Equivalently, in type $A$, a word written on a circle can be both sorted and antisorted by elementary bubble sort operators. We further show that the level $0$ representation is a calibrated principal series representation $M(t)$ for a suitable choice of character $t$, so that the quotient factors (non trivially) through the principal central specialization. This explains in particular the similarities between the representation theory of the classical $0$-Hecke algebra and that of the affine Hecke algebra at this specialization.
L'algèbre de Hecke groupe $\operatorname{H} \mathring{W}$ d'un groupe de Coxeter fini $\mathring{W}$, introduite par le premier et le dernier auteur, est obtenue en recollant de manière appropriée son algèbre de Hecke dégénérée et son algèbre de groupe. Dans cet article, nous donnons une construction alternative dans le cas où $\mathring{W}$ est un groupe de Weyl associé à un groupe de Weyl affine $W$. Plus précisément, nous montrons que quand $q$ n'est ni nul ni une racine de l'unité, $\operatorname{H} \mathring{W}$ est le quotient naturel de l'algèbre de Hecke affine $\operatorname{H}(W)(q)$ dans sa représentation de niveau $0$. Nous montrons de plus que la représentation de niveau $0$ est une représentation de série principale calibrée $M(t)$ pour un certain caractère $t$, de sorte que le quotient se factorise par la spécialisation centrale principale. Ce fait explique en particulier les similarités entre les théories des représentations de l'algèbre de Hecke dégénérée et de l'algèbre de Hecke affine sous cette spécialisation.
A Quantization of a theorem of Goulden and Jackson
Authors: Konvalinka Matjaž , Skandera Mark 
Published: August 2021

A theorem of Goulden and Jackson which gives interesting formulae for character immanants also implies MacMahon's Master Theorem. We quantize Goulden and Jackson's theorem to give formulae for quantum character immanants in such a way as to obtain a known quantization of MacMahon's Master Theorem due to Garoufalidis-Lê-Zeilberger. In doing so, we also quantize formulae of Littlewood, Merris and Watkins concerning induced character immanants.
Le Théorème Master de MacMahon peut être vu comme un corollaire d'un résultat de Goulden et Jackson décrivant certaines formules satisfaites par les caractères immanants. Dans cet article, on obtient une version quantique des formules de Goulden et Jackson, ce qui permet de donner une nouvelle preuve du résultat de Garoufalidis, Lê et Zeilberger sur la quantification du Théorème Master de MacMahon. Ce faisant, on arrive aussi à quantifier les formules de Littlewood, Merris et Watkins concernant les caractères immanants induits.
Affine descents and the Steinberg torus
Authors: Dilks Kevin , Petersen T. Kyle , Stembridge John R. 
Published: August 2021

Let $W \ltimes L$ be an irreducible affine Weyl group with Coxeter complex $\Sigma$, where $W$ denotes the associated finite Weyl group and $L$ the translation subgroup. The Steinberg torus is the Boolean cell complex obtained by taking the quotient of $\Sigma$ by the lattice $L$. We show that the ordinary and flag $h$-polynomials of the Steinberg torus (with the empty face deleted) are generating functions over $W$ for a descent-like statistic first studied by Cellini. We also show that the ordinary $h$-polynomial has a nonnegative $\gamma$-vector, and hence, symmetric and unimodal coefficients. In the classical cases, we also provide expansions, identities, and generating functions for the $h$-polynomials of Steinberg tori.
Nous considérons un groupe de Weyl affine irréductible $W \ltimes L$ avec complexe de Coxeter $\Sigma$, où $W$ désigne le groupe de Weyl fini associé et $L$ le sous-groupe des translations. Le tore de Steinberg est le complexe cellulaire Booléen obtenu comme le quotient de $\Sigma$ par $L$. Nous montrons que les $h$-polynômes, ordinaires et de drapeaux, du tore de Steinberg (sans la face vide) sont des fonctions génératrices sur $W$ pour une statistique de type descente, étudiée en premier lieu par Cellini. Nous montrons également qu'un $h$-polynôme ordinaire possède un $\gamma$-vecteur positif, et par conséquent, a des coefficients symétriques et unimodaux. Dans les cas classiques, nous donnons également des développements, des identités et des fonctions génératrices pour les $h$-polynômes des tores de Steinberg.
Equivalences for pattern avoiding involutions and classification
Authors: Dukes Mark , Jelínek Vít , Mansour Toufik , Reifegerste Astrid 
Published: August 2021

We complete the Wilf classification of signed patterns of length 5 for both signed permutations and signed involutions. New general equivalences of patterns are given which prove Jaggard's conjectures concerning involutions in the symmetric group avoiding certain patterns of length 5 and 6. In this way, we also complete the Wilf classification of $S_5$, $S_6$, and $S_7$ for both permutations and involutions.
Nous complétons la classification de Wilf des motifs signés de longueur 5 à la fois pour les permutations signées et les involutions signées. Nous donnons de nouvelles équivalences générales de motifs qui prouvent les conjectures de Jaggard concernant les involutions dans le groupe symétrique évitant certains motifs de longueur 5 et 6. De cette manière nous complétons également la classification de Wilf de $S_5$, $S_6$ et $S_7$ à la fois pour les permutations et les involutions.
Waiting time distributions for pattern occurrence in a constrained sequence
Authors: Stefanov Valeri T. , Szpankowski Wojciech 
Published: August 2021

Analysis of Algorithms
A binary sequence of zeros and ones is called a (d; k)-sequence if it does not contain runs of zeros of length either lessthan d or greater than k, where d and k are arbitrary, but fixed, non-negative integers and d < k. Such sequences find requires that (d; k)-sequences do not contain a specific pattern w. Therefore, distribution results concerning pattern occurrence in (d; k)-sequences are of interest. In this paper we study the distribution of the waiting time until the r-th occurrence of a pattern w in a random (d; k)-sequence generated by a Markov source. Numerical examples are also provided.
A combinatorial and probabilistic study of initial and end heights of descents in samples of geometrically distributed random variables and in permutations
Authors: Louchard Guy , Prodinger Helmut 
Published: August 2021

Analysis of Algorithms
In words, generated by independent geometrically distributed random variables, we study the lth descent, which is, roughly speaking, the lth occurrence of a neighbouring pair ab with a>b. The value a is called the initial height, and b the end height. We study these two random variables (and some similar ones) by combinatorial and probabilistic tools. We find in all instances a generating function Ψ(v,u), where the coefficient of vjui refers to the jth descent (ascent), and i to the initial (end) height. From this, various conclusions can be drawn, in particular expected values. In the probabilistic part, a Markov chain model is used, which allows to get explicit expressions for the heights of the second descent. In principle, one could go further, but the complexity of the results forbids it. This is extended to permutations of a large number of elements. Methods from q-analysis are used to simplify the expressions. This is the reason that we confine ourselves to the geometric distribution only. For general discrete distributions, no such tools are available.
Elements in finite classical groups whose powers have large 1-Eigenspaces
Authors: Niemeyer Alice , Praeger Cheryl 
Published: August 2021

Special issue in honor of Laci Babai's 60th birthday
We estimate the proportion of several classes of elements in finite classical groups which are readily recognised algorithmically, and for which some power has a large fixed point subspace and acts irreducibly on a complement of it. The estimates are used in complexity analyses of new recognition algorithms for finite classical groups in arbitrary characteristic.
On the size of induced acyclic subgraphs in random digraphs
Authors: Spencer Joel , Subramanian C.R. 
Published: August 2021

Graphs and Algorithms
Let D ∈ D(n, p) denote a simple random digraph obtained by choosing each of the (n 2) undirected edges independently with probability 2p and then orienting each chosen edge independently in one of the two directions with equal probability 1/2. Let mas(D) denote the maximum size of an induced acyclic subgraph in D. We obtain tight concentration results on the size of mas(D). Precisely, we show that $mas(D) \le \frac{2}{ln(1-p)^-1} (ln np + 3e)$ almost surely, provided p ≥ W/n for some fixed constant W. This combined with known and new lower bounds shows that (for p satisfying p = ω(1/n) and p ≤ 0.5) $mas(D) = \frac{2(ln np)}{ln(1-p)^-1} (1± o(1))$. This proves a conjecture stated by Subramanian in 2003 for those p such that p = ω(1/n). Our results are also valid for the random digraph obtained by choosing each of the n(n − 1) directed edges independently with probability p.
On the k-restricted structure ratio in planar and outerplanar graphs
Authors: Călinescu Gruia , Fernandes Cristina G. 
Published: August 2021

Graphs and Algorithms
A planar k-restricted structure is a simple graph whose blocks are planar and each has at most k vertices. Planar k-restricted structures are used by approximation algorithms for Maximum Weight Planar Subgraph, which motivates this work. The planar k-restricted ratio is the infimum, over simple planar graphs H, of the ratio of the number of edges in a maximum k-restricted structure subgraph of H to the number edges of H. We prove that, as k tends to infinity, the planar k-restricted ratio tends to 1 = 2. The same result holds for the weighted version. Our results are based on analyzing the analogous ratios for outerplanar and weighted outerplanar graphs. Here both ratios tend to 1 as k goes to infinity, and we provide good estimates of the rates of convergence, showing that they differ in the weighted from the unweighted case.
Simultaneous generation for zeta values by the Markov-WZ method
Authors: Pilehrood Khodabakhsh Hessami , Pilehrood Tatiana Hessami 
Published: August 2021

Combinatorics
By application of the Markov-WZ method, we prove a more general form of a bivariate generating function identity containing, as particular cases, Koecher's and Almkvist-Granville's Apéry-like formulae for odd zeta values. As a consequence, we get a new identity producing Apéry-like series for all ζ(2n+4m+3),n,m ≥ 0, convergent at the geometric rate with ratio 2−10.
Extremal K_(s,t)-free bipartite graphs
Authors: Balbuena Camino , García-Vázquez P. , Marcote Xavier , Valenzuela J. C. 
Published: August 2021

Graphs and Algorithms
In this paper new exact values of the Zarankiewicz function z(m,n;s,t) are obtained assuming certain requirements on the parameters. Moreover, all the corresponding extremal graphs are characterized. Finally, an extension of this problem to 3-partite graphs is studied.
Recurrence among trees with most numerous efficient dominating sets
Authors: Bród Dorota , Skupień Zdzisław 
Published: August 2021

Graphs and Algorithms
A dominating set D of vertices in a graph G is called an efficient dominating set if the distance between any two vertices in D is at least three. A tree T of order n is called maximum if T has the largest number of efficient dominating sets among all n-vertex trees. A constructive characterization of all maximum trees is given. Their structure has recurring aspects with period 7. Moreover, the number of efficient dominating sets in maximum n-vertex trees is determined and is exponential. Also the number of maximum n-vertex trees is shown to be bounded below by an increasing exponential function in n.
VC-dimensions of random function classes
Authors: Ycart Bernard , Ratsaby Joel 
Published: August 2021

Combinatorics
For any class of binary functions on [n]={1, ..., n} a classical result by Sauer states a sufficient condition for its VC-dimension to be at least d: its cardinality should be at least O(nd-1). A necessary condition is that its cardinality be at least 2d (which is O(1) with respect to n). How does the size of a 'typical' class of VC-dimension d compare to these two extreme thresholds ? To answer this, we consider classes generated randomly by two methods, repeated biased coin flips on the n-dimensional hypercube or uniform sampling over the space of all possible classes of cardinality k on [n]. As it turns out, the typical behavior of such classes is much more similar to the necessary condition; the cardinality k need only be larger than a threshold of 2d for its VC-dimension to be at least d with high probability. If its expected size is greater than a threshold of O(&log;n) (which is still significantly smaller than the sufficient size of O(nd-1)) then it shatters every set of size d with high probability. The behavior in the neighborhood of these thresholds is described by the asymptotic probability distribution of the VC-dimension and of the largest d such that all sets of size d are shattered.
Directed figure codes are decidable
Authors: Kolarz Michal , Moczurad Wlodzimierz 
Published: August 2021

Automata, Logic and Semantics
Two-dimensional structures of various kinds can be viewed as generalizations of words. Codicity verification and the defect effect, important properties related to word codes, are studied also in this context. Unfortunately, both are lost in the case of two common structures, polyominoes and figures. We consider directed figures defined as labelled polyominoes with designated start and end points, equipped with catenation operation that uses a merging function to resolve possible conflicts. We prove that in this setting verification whether a given finite set of directed figures is a code is decidable and we give a constructive algorithm. We also clarify the status of the defect effect for directed figures.
Self-complementing permutations of k-uniform hypergraphs
Authors: Szymański Artur , Wojda Adam Pawel 
Published: August 2021

Graphs and Algorithms
A k-uniform hypergraph H = ( V; E) is said to be self-complementary whenever it is isomorphic with its complement (H) over bar = ( V; ((V)(k)) - E). Every permutation sigma of the set V such that sigma(e) is an edge of (H) over bar if and only if e is an element of E is called self-complementing. 2-self-comlementary hypergraphs are exactly self complementary graphs introduced independently by Ringel ( 1963) and Sachs ( 1962). <br> For any positive integer n we denote by lambda(n) the unique integer such that n = 2(lambda(n)) c, where c is odd. <br> In the paper we prove that a permutation sigma of [1, n] with orbits O-1,..., O-m O m is a self-complementing permutation of a k-uniform hypergraph of order n if and only if there is an integer l >= 0 such that k = a2(l) + s, a is odd, 0 <= s <= 2(l) and the following two conditions hold: <br> (i)n = b2(l+1) + r,r is an element of {0,..., 2(l) - 1 + s}, and <br> (ii) Sigma(i:lambda(vertical bar Oi vertical bar)<= l) vertical bar O-i vertical bar <= r. <br> For k = 2 this result is the very well known characterization of self-complementing permutation of graphs given by Ringel and Sachs.
A characterization of infinite smooth Lyndon words
Authors: Paquin Geneviève 
Published: August 2021

Combinatorics
In a recent paper, Brlek, Jamet and Paquin showed that some extremal infinite smooth words are also infinite Lyndon words. This result raises a natural question: are they the only ones? If no, what do the infinite smooth words that are also Lyndon words look like? In this paper, we give the answer, proving that the only infinite smooth Lyndon words are m(\a ...
Tight Bounds for Delay-Sensitive Aggregation
Authors: Pignolet Yvonne Anne , Schmid Stefan , Wattenhofer Roger 
Published: August 2021

Distributed Computing and Networking
This article studies the fundamental trade-off between delay and communication cost in networks. We consider an online optimization problem where nodes are organized in a tree topology. The nodes seek to minimize the time until the root is informed about the changes of their states and to use as few transmissions as possible. We derive an upper bound on the competitive ratio of O(min (h, c)) where h is the tree's height, and c is the transmission cost per edge. Moreover, we prove that this upper bound is tight in the sense that any oblivious algorithm has a ratio of at least Omega(min (h, c)). For chain networks, we prove a tight competitive ratio of Theta(min (root h, c)). Furthermore, we introduce a model for value-sensitive aggregation, where the cost depends on the number of transmissions and the error at the root.
On a 1, 2 Conjecture
Authors: Przybylo Jakub , WoźniaK Mariusz 
Published: August 2021

Graphs and Algorithms
Let us assign positive integers to the edges and vertices of a simple graph G. As a result we obtain a vertex-colouring of G with integers, where a vertex colour is simply a sum of the weight assigned to the vertex itself and the weights of its incident edges. Can we obtain a proper colouring using only weights 1 and 2 for an arbitrary G? We give a positive answer when G is a 3-colourable, complete or 4-regular graph. We also show that it is enough to C use weights from 1 to 11, as well as from 1 to 11 [chi(G)/2] + 1, for an arbitrary graph G.
Covering codes in Sierpinski graphs
Authors: Beaudou Laurent , Gravier Sylvain , Klavžar Sandi , Kovse Matjaz , Mollard Michel 
Published: August 2021

Graphs and Algorithms
For a graph G and integers a and b, an (a, b)-code of G is a set C of vertices such that any vertex from C has exactly a neighbors in C and any vertex not in C has exactly b neighbors in C. In this paper we classify integers a and b for which there exist (a, b)-codes in Sierpinski graphs.
Deterministic recognizability of picture languages with Wang automata
Authors: Lonati Violetta , Pradella Matteo 
Published: August 2021

special issue dedicated to the second edition of the conference AutoMathA: from Mathematics to Applications
We present a model of automaton for picture language recognition, called Wang automaton, which is based on labeled Wang tiles. Wang automata combine features of both online tessellation acceptors and 4-way automata: as in online tessellation acceptors, computation assigns states to each picture position; as in 4-way automata, the input head visits the picture moving from one pixel to an adjacent one, according to some scanning strategy. Wang automata recognize the class REC, i.e. they are equivalent to tiling systems or online tessellation acceptors, and hence strictly more powerful than 4-way automata. We also introduce a natural notion of determinism for Wang automata, and study the resulting class, extending the more traditional approach of diagonal-based determinism, used e. g. by deterministic tiling systems. In particular, we prove that the concept of row (or column) ambiguity defines the class of languages recognized by Wang automata directed by boustrophedonic scanning strategies.
Crucial abelian k-power-free words
Authors: Glen Amy , Halldorsson Bjarni V. , Kitaev Sergey 
Published: August 2021

Combinatorics
In 1961, Erdos asked whether or not there exist words of arbitrary length over a fixed finite alphabet that avoid patterns of the form XX' where X' is a permutation of X (called abelian squares). This problem has since been solved in the affirmative in a series of papers from 1968 to 1992. Much less is known in the case of abelian k-th powers, i.e., words of the form X1X2 ... X-k where X-i is a permutation of X-1 for 2 <= i <= k. In this paper, we consider crucial words for abelian k-th powers, i. e., finite words that avoid abelian k-th powers, but which cannot be extended to the right by any letter of their own alphabets without creating an abelian k-th power. More specifically, we consider the problem of determining the minimal length of a crucial word avoiding abelian k-th powers. This problem has already been solved for abelian squares by Evdokimov and Kitaev (2004), who showed that a minimal crucial word over an n-letter alphabet A(n) = \1, 2, ..., n\ avoiding abelian squares has length 4n - 7 for n >= 3. Extending this result, we prove that a minimal crucial word over A(n) avoiding abelian cubes has length 9n - 13 for n >= 5, and it has length 2, 5, 11, and 20 for n = 1, 2, 3, and 4, respectively. Moreover, for n >= 4 and k >= 2, we give a construction of length k(2) (n - 1) - k - 1 of a crucial word over A(n) avoiding abelian k-th powers. This construction gives the minimal length for k = 2 and k = 3. For k >= 4 and n >= 5, we provide a lower bound for the length of crucial words over A(n) avoiding abelian k-th powers.