Grant Cairns, Stacey Mendan
We show that if the two parts of a finite bipartite graph have the same degree sequence, then there is a bipartite graph, with the same degree sequences, which is symmetric, in that it has an involutive graph automorphism that interchanges its two parts. To prove this, we study the relationship between symmetric bipartite graphs and graphs with loops.
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We study the equivalence between bipartiteness and symmetry of spectra of mixed graphs, for $θ$-Hermitian adjacency matrices defined by an angle $θ\in (0, π]$. We show that this equivalence holds when, for example, an angle $θ$ is an algebraic number, while it breaks down for any angle $θ\in \mathbb{Q}π$. Furthermore, we construct a family of non-bipartite mixed graphs having the symmetric spectra for given $θ\in \mathbb{Q}π$.
Link between bipartite and general unicellular toroidal maps via slit--slide--sew bijections
通过切口-滑动-缝合双射将一般图与双侧图联系起来，利用特定循环的旋转操作改变循环长度的奇偶性，从而在单细胞扭折图中建立完整对应关系。
The signed graphs with symmetric spectra
本文研究具有对称谱的符号图的刻画问题，给出了谱对称符号图的必要和（或）充分条件，并提出了构造此类符号图的方法，生成了无限族符号图。
Intuitively speaking, a bipartite graph is mirror if it can be drawn in the Cartesian plane in such a way that, the vertices of one stable are points in x=0, the vertices of the other stable set are points in x=1, the edges are straight line segments joining adjacent vertices and the resulting configuration is symmetric with respect to the line x=1/2. The concept of mirror bipartite graph appears naturally when studying certain types of products of graphs as for instance the Kronecker product. Motivated by this fact, we study mirror bipartite graphs from the point of view of their degree seque…
A signed graph is said to be sign-symmetric if it is switching isomorphic to its negation. Bipartite signed graphs are trivially sign-symmetric. We give new constructions of non-bipartite sign-symmetric signed graphs. Sign-symmetric signed graphs have a symmetric spectrum but not the other way around. We present constructions of signed graphs with symmetric spectra which are not sign-symmetric. This, in particular answers a problem posed by Belardo, Cioabă, Koolen, and Wang (2018).
For finite sequence $\underbar{\em d}$ of positive integers, we consider graphs that have $\underbar{\em d}$ as their list of vertex degrees, and bipartite graphs for which each part has $\underbar{\em d}$ as its list of vertex degrees. In particular, we make a connection between a result for bipartite graphs by Alon, Ben-Shimon and Krivelevich and a result of Zverovich and Zverovich for graphs, and we give an improvement of a result of Zverovich and Zverovich. We show that the bipartite graphs with vertex degree sequences $(\underbar{\em d},\underbar{\em d}\,)$ are in one to one correspondenc…
Sufficient conditions for bipartite rigidity, symmetric completability and hyperconnectivity of graphs
本文研究了三种图的matroid，给出图在这些matroid中达到最大可能秩的充分条件，并探讨了低秩矩阵唯一可补全性的 implications。
Kang and Park recently showed that every cubic (loopless) multigraph is incidence 6-choosable [On incidence choosability of cubic graphs. \emph{arXiv}, April 2018]. Equivalently, every bipartite graph obtained by subdividing once every edge of a cubic graph, is strongly 6-edge-choosable. The aim of this note is to give a shorter proof of their result by looking at the strong edge-coloring formulation of the problem.
A bipartite graph is {\em pseudo 2--factor isomorphic} if all its 2--factors have the same parity of number of circuits. In \cite{ADJLS} we proved that the only essentially 4--edge-connected pseudo 2--factor isomorphic cubic bipartite graph of girth 4 is $K_{3,3}$, and conjectured \cite[Conjecture 3.6]{ADJLS} that the only essentially 4--edge-connected cubic bipartite graphs are $K_{3,3}$, the Heawood graph and the Pappus graph. There exists a characterization of symmetric configurations $n_3$ %{\bf decide notation and how to use it in the rest of the paper} due to Martinetti (1886) in which a…
We provide asymptotic formulae for the numbers of bipartite graphs with given degree sequence, and of loopless digraphs with given in- and out-degree sequences, for a wide range of parameters. Our results cover medium range densities and close the gaps between the results known for the sparse and dense ranges. In the case of bipartite graphs, these results were proved by Greenhill, McKay and Wang in 2006 and by Canfield, Greenhill and McKay in 2008, respectively. Our method also essentially covers the sparse range, for which much less was known in the case of loopless digraphs. For the range o…
Let $G$ be a bipartite graph and its adjacency matrix $\mathbb A$. If $G$ has a unique perfect matching, then $\mathbb A$ has an inverse $\mathbb A^{-1}$ which is a symmetric integral matrix, and hence the adjacency matrix of a multigraph. The inverses of bipartite graphs with unique perfect matchings have a strong connection to Möbius functions of posets. In this note, we characterize all bipartite graphs with a unique perfect matching whose adjacency matrices have inverses diagonally similar to non-negative matrices, which settles an open problem of Godsil on inverses of bipartite graphs in …
P-Polynomial and Bipartite Coherent Configurations
本文引入P-多项式相干构形并证明其最多两纤维，提出双纤维相干构形类，其相干代数具双特殊基，包含距离双正则图P-多项式类、拟对称设计等实例。
Let $G$ be a bipartite graph without loops and multiple edges on $v\ge 4$ vertices, which can be drawn on the plane such that any edge intersects at most one other edge. We prove that such graph has at most $3v-8$ edges for even $v\ne 6$ and at most $3v-9$ edges for odd $v$ and $v=6$. For all $v\ge 4$ examples showing that these bounds are tight are constructed. In the end of paper we discuss a question about drawings of complete bipartite graphs on the plane such that any edge intersects at most one other edge. {\sc Keywords:} topological graphs, planar graphs, bipartite graphs.
In the present paper, exterior algebraic shifting and symmetric algebraic shifting of bipartite graphs and chordal graphs are studied. First, we will determine the symmetric algebraic shifted graph of complete bipartite graphs. It turns out that, for $a>3$ and $b>3$, the exterior algebraic shifted graph of the complete bipartite graph $K_{a,b}$ of size $a,b$ is different from the symmetric algebraic shifted graph of $K_{a,b}$. Second, we will show that the exterior algebraic shifted graph of any chordal graph $G$ is coincident with the symmetric algebraic shifted graph of $G$.
We construct infinitely many signed graphs having symmetric spectrum, by using the NEPS and rooted product of signed graphs. We also present a method for constructing large cospectral signed graphs. Although the obtained family contains only a minority of signed graphs, it strengthen the belief that the signed graphs with symmetric spectrum are deeper than bipartite graphs, i.e the unsigned graphs with symmetric spectrum.
In this paper we consider the separability problem for bipartite quantum states arising from graphs. Earlier it was proved that the degree criterion is the graph-theoretic counterpart of the familiar positive partial transpose criterion for separability, although there are entangled states with positive partial transpose for which the degree criterion fails. Here we introduce the concept of partially symmetric graphs and degree symmetric graphs by using the well-known concept of partial transposition of a graph and degree criteria, respectively. Thus, we provide classes of bipartite separable …
Characterizing bipartite distance-regularized graphs with vertices of eccentricity 4
本文证明特定参数与交数条件下的拟对称SPBIBD关联图，同$D=D'=4$的二分距离正则化图一一对应，从而刻画含离心率4顶点的图类。
On the Automorphism Group of Token Graphs of Complete Bipartite Graphs
本文研究完全二分图 $K_{m,n}$ 的 $k$-令牌图，完整刻画了其自同构群的结构。
Strong chordality in tournaments and multipartite tournaments with possible loops
本文研究可能带环的多部锦标赛的强弦性，给出多项式时间识别算法与禁用导出子图刻画，并证明强弦有向图中全控制集最小规模等于不相交入邻域最大数目且可在线性时间内计算。
Given an Eulerian digraph, we consider the genus distribution of its face-oriented embeddings. We prove that such distribution is log-concave for two families of Eulerian digraphs, thus giving a positive answer for these families to a question asked in Bonnington, Conder, Morton and McKenna (2002). Our proof uses real-rooted polynomials and the representation theory of the symmetric group $\mathbb{S}_n$. The result is also extended to some factorizations of the identity in $\mathbb{S}_n$ that are rotation systems of some families of one-face constellations.
Spectrally symmetric orientations of graphs
本文研究了非二分图的谱对称定向图，探讨了其密度极值问题及构造方法。
Asymptotic enumeration of constrained bipartite, directed and oriented graphs by degree sequence
本文研究了约束双图、有向图和定向图的渐近计数问题，提出了基于度序列的概率方法，并应用到随机矩阵的永久性计算及无向图定向的度数分析中。
Some Results On Spectrum And Energy Of Graphs With Loops
本文研究带环图的谱与能量，建立二部性与谱之间的充要条件，证明二部图中加环不降低能量，并刻画完全图、完全二部图及特征值正负性受限的带环图。
A road interchange where $n$ roads meet and in which the drivers are not allowed to change lanes can be modelled as an embedding of a 2-coloured (hence bipartite) multigraph $G$ with equal-sized colour classes into an orientable surface such that there is a face bounded by a Hamiltonian cycle (Kurauskas, 2017). The case of $G$ a complete bipartite graph $K_{n,n}$ corresponds to a complete $n$-way interchange where drivers approaching from each of $n$ directions can exit to any other direction. The genus of the underlying surface can be interpreted as the number of bridges in the interchange. I…
Graph Polynomials for the Numbers of Independent Sets and Bipartite Cuts for Undirected Graphs
本文用顶点单项式的初等对称多项式刻画无向图独立集计数，并据此导出团、顶点覆盖及二部割的图多项式表示。
Graphs with Bipartite Complement that Admit Two Distinct Eigenvalues
本文研究图的最小不同特征值数q(G)，证明补图边数不超过⌊n/2⌋-1时q(G)=2，并针对二部补图情形验证了q(G)=2的猜想，同时刻画了边数为n-2时q(G)>2的图。
A resolving set for a graph $Γ$ is a collection of vertices $S$, chosen so that for each vertex $v$, the list of distances from $v$ to the members of $S$ uniquely specifies $v$. The metric dimension $μ(Γ)$ is the smallest size of a resolving set for $Γ$. We consider the metric dimension of two families of incidence graphs: incidence graphs of symmetric designs, and incidence graphs of symmetric transversal designs (i.e. symmetric nets). These graphs are the bipartite distance-regular graphs of diameter $3$, and the bipartite, antipodal distance-regular graphs of diameter $4$, respectively. In …
The Cycle Rank Threshold: Perfect Matchings and Bipartite Parter Graphs
本文确定二分图中使性质(P)等价于存在完美匹配的最大圈秩，将该等价关系从圈秩≤3推广到圈秩为4并证明其界是紧的。
In this expository paper we describe a group theoretic characterization of arc-transitive graphs and their quotients. When passing from a symmetric graph to its quotient, much information is lost, but some of this information may be recovered from a certain combinatorial design on the blocks, as well as a bipartite graph between the blocks. We address the "extention problem" which asks, when is this additional information sufficient to recover the original graph?
Let $x,y\in(0,1]$ and let $A,B,C$ be disjoint nonempty subsets of a graph $G$, where every vertex in $A$ has at least $x|B|$ neighbours in $B$, and every vertex in $B$ has at least $y|C|$ neighbours in $C$. We denote by $ϕ(x,y)$ the maximum $z$ such that, in all such graphs $G$, there is a vertex $v$ in $C$ that is joined to at least $z|A|$ vertices in $A$ by two-edge paths. The function $ϕ$ is interesting, and we investigate some of its properties. For instance, we show that it is symmetric in $x$ and $y$, and that it has a discontinuity at $x=y=1/k$ for all integers $k>1$. We raise a number …
Let Q be a Dynkin quiver of type A. The bounded derived category of the path algebra of Q has an autoequivalence given by the composition of the Auslander-Reiten translate and the square of the shift functor. We classify the maximal rigid objects in the corresponding orbit category C(Q), in terms of bipartite noncrossing graphs (with loops) in a circle. We also describe the endomorphism algebras of the maximal rigid objects, and we prove that a certain class of these algebras are iterated tilted algebras of type A.
We introduce a new notation for representing labeled regular bipartite graphs of arbitrary degree. Several enumeration problems for labeled and unlabeled regular bipartite graphs have been introduced. A general algorithm for enumerating all non-isomorphic 2-regular bipartite graphs for a specified number of vertices has been described and a mathematical proof has been provided for its completeness. An abstraction of m Symmetric Permutation Tree in order to visualize a labeled r-Regular Bipartite Graph with 2m vertices and enumerate its automorphism group has been introduced. An algorithm to ge…
A recent result of one of the authors says that every connected subcubic bipartite graph that is not isomorphic to the Heawood graph has at least one, and in fact a positive proportion of its eigenvalues in the interval [-1,1]. We construct an infinite family of connected cubic bipartite graphs which have no eigenvalues in the open interval (-1,1), thus showing that the interval [-1,1] cannot be replaced by any smaller symmetric subinterval even when allowing any finite number of exceptions. Similar examples with vertices of larger degrees are considered and it is also shown that their eigenva…
A 60-Vertex Lower Bound for Cubic Bipartite Counterexamples to the Erdős-Gyárfás Conjecture
本研究通过穷举计算将Erdős-Gyárfás猜想的立方二分反例的顶点下界从30提升至60，验证了顶点数≤58的简单立方二分图必含4、8或16环，证明过程结合Moore界、Levi图转化与受限增长搜索，结果经多重方式验证。
Let $X=(V, E)$ be a finite regular graph and $H_t(u, v), \, u, v \in V$, the heat kernel on $X$. We prove that, if the graph $X$ is bipartite and has four distinct Laplacian eigenvalues, the ratio $H_t(u, v)/H_t(u, u), \, u, v \in V,$ is monotonically non-decreasing as a function of $t$. The key to the proof is the fact that such a graph is an incidence graph of a symmetric 2-design.
In this paper, we consider the Hessian matrices $H_Γ$ of the complete and complete bipartite graphs, and the special value of $\tilde H_Γ$ at $x_{i}=1$ for all $x_{i}$. We compute the eigenvalues of $\tilde H_Γ$. We show that one of them is positive and that the others are negative. In other words, the metric with respect to the symmetric matrix $\tilde H_Γ$ is Lorentzian. Hence those Hessian $\det (H_Γ)$ are not identically zero. As an application, we show the strong Lefschetz property for the Artinian Gorenstein algebra associated to the graphic matroids of the complete and complete bipartit…
The quantities C_4 and Theta_2,2,2 are as defined by Wanless, C_4 just the number of 4-loops of a graph. The construction of this paper provides a counterexample to a conjecture of Butera, Pernici, and the author about the monomer-dimer entropy, lambda, of a regular bipartite lattice. The lattice we construct is not a lattice graph in its most common definition.
We define strongly chordal digraphs, which generalize strongly chordal graphs and chordal bipartite graphs, and are included in the class of chordal digraphs. They correspond to square 0,1 matrices that admit a simultaneous row and column permutation avoiding the Γ matrix. In general, it is not clear if these digraphs can be recognized in polynomial time, and we focus on symmetric digraphs (i.e., graphs with possible loops), tournaments with possible loops, and balanced digraphs. In each of these cases we give a polynomial-time recognition algorithm and a forbidden induced subgraph characteriz…
We present a generalization of the marriage problem underlying Hall's famous Marriage Theorem to what we call the Symmetric Marriage Problem, a problem that can be thought of as a special case of Maximal Weighted Bipartite Matching. We show that there is a solution to the Symmetric Marriage Problem if and only if a variation on Hall's Condition holds on each of the bipartitions. We prove both finite and infinite versions of this result and provide applications. We also introduce a non-bipartite version of the problem and show that a generalization of Tutte's Theorem applies.
Conjugacy Class Averages and Sidorenko's Conjecture
通过共轭类平均约化，证明若每个Cayley型宿主图的H-密度不小于其共轭类平均的H-密度，则H是强Sidorenko图，进而满足Sidorenko猜想；并证明了有限群上任意实值函数对应的共轭平均Cayley核的1-细分图满足Sidorenko型不等式。
Let $G$ be a finite, undirected $d$-regular graph and $A(G)$ its normalized adjacency matrix, with eigenvalues $1 = λ_1(A)\geq \dots \ge λ_n \ge -1$. It is a classical fact that $λ_n = -1$ if and only if $G$ is bipartite. Our main result provides a quantitative separation of $λ_n$ from $-1$ in the case of Cayley graphs, in terms of their expansion. Denoting $h_{out}$ by the (outer boundary) vertex expansion of $G$, we show that if $G$ is a non-bipartite Cayley graph (constructed using a group and a symmetric generating set of size $d$) then $λ_n \ge -1 + ch_{out}^2/d^2\,,$ for $c$ an absolute …
These are notes for my talk at ICCM 2010, Beijing. We survey some results, obtained jointly with Pavlo Pylyavskyy, concerning the ring of loop symmetric functions. Motivations from networks on surfaces, total positivity, crystal graphs, and discrete integrable systems are discussed.
The focus of this paper is on discussion of a catalog of a class of (3, g) graphs for even girth g. A (k, g) graph is a graph with regular degree k and girth g. This catalog is compared with other known lists of (3, g) graphs such as the enumerations of trivalent symmetric graphs and enumerations of trivalent vertex-transitive graphs, to conclude that this catalog has graphs for more orders than these lists. This catalag also specifies a list of orders, rotational symmetry and girth for which the class of (3, g) graphs do not exist. It is also shown that this catalog of graphs extends infinite…
We consider the O(n) loop model on tetravalent maps and show how to rephrase it into a model of bipartite maps without loops. This follows from a combinatorial decomposition that consists in cutting the O(n) model configurations along their loops so that each elementary piece is a map that may have arbitrary even face degrees. In the induced statistics, these maps are drawn according to a Boltzmann distribution whose parameters (the face weights) are determined by a fixed point condition. In particular, we show that the dense and dilute critical points of the O(n) model correspond to bipartite…
In this paper, we study eigenvalues and eigenfunctions of $p$-Laplacians with Dirichlet boundary condition on graphs. We characterize the first eigenfunction (and the maximum eigenfunction for a bipartite graph) via the sign condition. By the uniqueness of the first eigenfunction of $p$-Laplacian, as $p\to 1,$ we identify the Cheeger constant of a symmetric graph with that of the quotient graph. By this approach, we calculate various Cheeger constants of spherically symmetric graphs.
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