Mark K. Goldberg
We present a novel algorithm for edge-coloring of multigraphs. The correctness of this algorithm for multigraphs with $χ' > Δ+1$ ($χ'$ is the chromatic edge number and $Δ$ is the maximum vertex degree) would prove a long standing conjecture in edge-coloring of multigraphs.
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Let G=(V,E) be a graph and let f be a function that assigns list sizes to the vertices of G. It is said that G is f-choosable if for every assignment of lists of colors to the vertices of G for which the list sizes agree with f, there exists a proper coloring of G from the lists. The sum choice number is the minimum of the sum of list sizes for f over all choosable functions f for G. The sum choice number of a graph is always at most the sum |V|+|E|. When the sum choice number of G is equal to this upper bound, G is said to be sc-greedy. In this paper, we determine the sum choice number of all…
Greedy Coloring and Simple Exponential Strengthenings of Brooks-Type Theorems
本文对布鲁克斯定理给出新证明，证明连通非完全且最大度Δ≥3的图存在指数多个正常Δ着色，还拓展技术到多种着色场景，给出新归约与度可选性定理的新证明。
The smallest number of edges forming an n-uniform hypergraph which is not r-colorable is denoted by m(n,r). Erdős and Lovász conjectured that m(n,2)=θ(n 2^n)$. The best known lower bound m(n,2)=Ω(sqrt(n/log(n)) 2^n) was obtained by Radhakrishnan and Srinivasan in 2000. We present a simple proof of their result. The proof is based on analysis of random greedy coloring algorithm investigated by Pluhár in 2009. The proof method extends to the case of r-coloring, and we show that for any fixed r we have m(n,r)=Ω((n/log(n))^(1-1/r) r^n) improving the bound of Kostochka from 2004. We also derive ana…
A measure theoretic approach of the problem that there exits a finite unit-distance graphs in the plane that are not five (or four) colorable.
Let $m^*(n)$ be the minimum number of edges in an $n$-uniform simple hypergraph that is not two colorable. We prove that $m^*(n)=Ω(4^n/\ln^2(n))$. Our result generalizes to $r$-coloring of $b$-simple uniform hypergraphs. For fixed $r$ and $b$ we prove that a maximum vertex degree in $b$-simple $n$-uniform hypergraph that is not $r$-colorable must be $Ω(r^n /\ln(n))$. By trimming arguments it implies that every such graph has $Ω((r^n /\ln(n))^{b+1/b})$ edges. For any fixed $r \geq 2$ our techniques yield also a lower bound $Ω(r^n/\ln(n))$ for van der Waerden numbers $W(n,r)$.
Cographs are exactly hereditarily well-colored graphs, i.e., the graphs for which a greedy coloring of every induced subgraph uses only the minimally necessary number of colors $χ(G)$. In recent work on reciprocal best match graphs so-called hierarchically coloring play an important role. Here we show that greedy colorings are a special case of hierarchical coloring, which also require no more than $χ(G)$ colors.
A connected ordering $(v_1, v_2, \ldots, v_n)$ of $V(G)$ is an ordering of the vertices such that $v_i$ has at least one neighbour in $\{v_1, \ldots, v_{i - 1}\}$ for every $i \in \{2, \ldots, n\}$. A connected greedy coloring (CGC for short) is a coloring obtained by applying the greedy algorithm to a connected ordering. This has been first introduced in 1989 by Hertz and de Werra, but still very little is known about this problem. An interesting aspect is that, contrary to the traditional greedy coloring, it is not always true that a graph has a connected ordering that produces an optimal co…
For integers $k, r > 0$, a conditional $(k,r)$-coloring of a graph $G$ is a proper $k$-coloring of the vertices of $G$ such that every vertex $v$ of degree $d(v)$ in $G$ is adjacent to at least $\min\{r, d(v)\}$ differently colored vertices. Given $r$, the smallest integer $k$ for which $G$ has a conditional $(k,r)$-coloring is called the $r$th order conditional chromatic number $χ_r(G)$ of $G$. We give results (exact values or bounds for $χ_r(G)$, depending on $r$) related to the conditional coloring of some graphs. We introduce \emph{unique conditional colorability} and give some related res…
The forb-flex method for odd coloring and proper conflict-free coloring of planar graphs
本研究提出贪心着色新工具forb-flex方法，结合放电法改进了平面图奇着色与正常无冲突着色的色数上界，优化了已有研究结果。
Let $G$ be a graph and $t$ a nonnegative integer. Suppose $f$ is a mapping from the vertex set of $G$ to $\{1,2,\dots, k\}$. If, for any vertex $u$ of $G$, the number of neighbors $v$ of $u$ with $f(v)=f(u)$ is less than or equal to $t$, then $f$ is called a $t$-relaxed $k$-coloring of $G$. And $G$ is said to be $(k,t)$-colorable. The $t$-relaxed chromatic number of $G$, denote by $χ_t(G)$, is defined as the minimum integer $k$ such that $G$ is $(k,t)$-colorable. A set $S$ of vertices in $G$ is $t$-sparse if $S$ induces a graph with a maximum degree of at most $t$. Thus $G$ is $(k,t)$-colorabl…
Randomized Greedy Online Edge Coloring Succeeds for Dense and Randomly-Ordered Graphs
本文分析在线边着色中的朴素随机贪心算法，证明其在随机边序或稠密图条件下可用$(1+ε)Δ$种颜色成功着色，并推出对抗自适应情形下的确定性算法。
Our work becomes integrated into the general problem of the stability of the network ad hoc. Some, works attacked this problem. Among these works, we find the modelling of the network ad hoc in the form of a graph. Thus the problem of stability of the network ad hoc which corresponds to a problem of allocation of frequency amounts to a problem of allocation of colors in the vertex of graph. we present use a parameter of coloring the number of Grundy. The Grundy number of a graph G, denoted by (G), is the largest k such that G has a greedy k-coloring, that is a coloring with colours obtained by…
For any graph $F$ and any integer $r\geq 2$, the \emph{online vertex-Ramsey density of $F$ and $r$}, denoted $m^*(F,r)$, is a parameter defined via a deterministic two-player Ramsey-type game (Painter vs.\ Builder). This parameter was introduced in a recent paper \cite{mrs11}, where it was shown that the online vertex-Ramsey density determines the threshold of a similar probabilistic one-player game (Painter vs.\ the binomial random graph $G_{n,p}$). For a large class of graphs $F$, including cliques, cycles, complete bipartite graphs, hypercubes, wheels, and stars of arbitrary size, a simple …
The greedy coloring algorithm shows that a graph of maximum degree at most $Δ$ has chromatic number at most $Δ+ 1$, and this is tight for cliques. Much attention has been devoted to improving this "greedy bound" for graphs without large cliques. Brooks famously proved that this bound can be improved by one if $Δ\geq 3$ and the graph contains no clique of size $Δ+ 1$. Reed's Conjecture states that the "greedy bound" can be improved by $k$ if the graph contains no clique of size $Δ+ 1 - 2k$. Johansson proved that the "greedy bound" can be improved by a factor of $Ω(\ln(Δ)^{-1})$ or $Ω\left(\frac…
Coloring hypergraphs that are the union of nearly disjoint cliques
本文研究由两两小交集团并集构成的超图最大色数，构造了团数量为多项式级的近似designs以证明其具有大色数，并通过随机贪婪超图过程对交集至多为1的情况给出下界，同时探讨了有限射影/仿影平面中最大caps数量的界。
We consider new parameters for conditional network vulnerability related to graph coloring. We define a network to be in operation if the chromatic number (or index) is greater than some specified value k. The parameters of interest, the minimum k- chromatic number and the minimum k-chromatic index consider the least number of failures in the network which could render the network inoperable. In this paper, we consider edge failure, vertex failures, as well as mixed failures for paths, cycles, and complete graphs.
The Grundy number of a graph is the maximum number of colors used by the greedy coloring algorithm over all vertex orderings. In this paper, we study the computational complexity of GRUNDY COLORING, the problem of determining whether a given graph has Grundy number at least $k$. We also study the variants WEAK GRUNDY COLORING (where the coloring is not necessarily proper) and CONNECTED GRUNDY COLORING (where at each step of the greedy coloring algorithm, the subgraph induced by the colored vertices must be connected). We show that GRUNDY COLORING can be solved in time $O^*(2.443^n)$ and WEAK G…
Grundy Packing Coloring of Graphs
本文提出图的 Grundy 填充色数 Γ_ρ(G)，用贪心多项式算法的最大着色值定义它，并研究其性质、复杂性、界与精确值。
On ${\rm b}^{\ast}$-Coloring and $z$-Coloring of graphs with high girth
该研究针对高围长图，运用列表着色技术推导了${\rm b}^*$-色数、$z$-色数的相关结论，丰富了图着色理论的成果。
Wild number for spanning trees in complete and complete bipartite graphs
该文研究完全图与完全二部图的野生数，确定均衡2-着色、最小真着色下的野生数范围与精确值，推导结构条件并分析贪心算法，还将结果应用于图笛卡尔积以得到相关下界。
A stronger upper bound on the D-chromatic index
该研究针对图的D-色指数的Brooks型上界问题，采用概率方法，首次改进了此前由贪心着色得到的上界，证明了最大度足够大时D-色指数不超过带正系数修正的二次上界。
Coloring the vertices of a graph with mutual-visibility property
本文提出图的互可见性着色及互可见性色数，研究其与色数、互可见性数的关系，给出参数界、贪心算法、笛卡尔积与冠积结果，并刻画二着色图。
A linear-time algorithm for $(1+ε)Δ$-edge-coloring
本文提出首个覆盖任意最大度范围的线性时间随机化算法，用于求解$(1+ε)Δ$-边着色问题，填补了此前即使$2Δ-1$色贪心界情形也无线性时间算法的空白。
Online coloring of short interval graphs and two-count interval graphs
本文研究了σ-区间图和两计数区间图的在线着色问题，证明了σ-区间图的在线着色竞争比下界为3，而两计数区间图的贪心算法First-Fit的竞争比为4，且在不同条件下给出了更优的竞争比下界。
On Grundy and b-chromatic number of some families of graphs: a comparative study
本文比较研究图的 Grundy 数与 b-色数，构造二者背离的图序列，并证明若干图族中 Grundy 数可由 b-色数的函数控制，从而验证相关猜想。
Graph colorings is a fundamental topic in graph theory that require an assignment of labels (or colors) to vertices or edges subject to various constraints. We focus on the harmonious coloring of a graph, which is a proper vertex coloring such that for every two distinct colors i, j at most one pair of adjacent vertices are colored with i and j. This type of coloring is edge-distinguishing and has potential applications in transportation network, computer network, airway network system. The results presented in this paper fall into two categories: in the first part of the paper we are concerne…
Neural Algorithmic Reasoning for Approximate $k$-Coloring with Recursive Warm Starts
本文提出利用图神经网络和递归预热启动方法改进近似k-着色，通过优化算法和局部搜索算法提升着色效率。
For given graph $H$ and graphical property $P$, the conditional chromatic number $χ(H,P)$ of $H$, is the smallest number $k$, so that $V(H)$ can be decomposed into sets $V_1,V_2,\ldots, V_k$, in which $H[V_i]$ satisfies the property $P$, for each $1\leq i\leq k$. When property $P$ be that each color class contains no copy of $G$, we write $χ_{G}(H)$ instead of $χ(G,P)$, which is called the $G$-free chromatic number. Due to this, we say $H$ has a $k$-$G$-free coloring if there is a map $c : V(H) \longrightarrow \{1,\ldots,k\}$, so that each of the color classes of $c$ be $G$-free. Assume that f…
In this paper we consider colorings of oriented graphs, i.e. digraphs without cycles of length 2. Given some oriented graph $G=(V,E)$, an oriented $r$-coloring for $G$ is a partition of the vertex set $V$ into $r$ independent sets, such that all the arcs between two of these sets have the same direction. The oriented chromatic number of $G$ is the smallest integer $r$ such that $G$ permits an oriented $r$-coloring. In this paper we consider the Oriented Chromatic Number problem on classes of recursively defined oriented graphs. Oriented co-graphs (short for oriented complement reducible graphs…
A 2-hued coloring of a graph $G$ (also known as conditional $(k, 2)$-coloring and dynamic coloring) is a coloring such that for every vertex $v\in V(G)$ of degree at least $2$, the neighbors of $v$ receive at least $2$ colors. The smallest integer $k$ such that $G$ has a 2-hued coloring with $ k $ colors, is called the {\it 2-hued chromatic number} of $G$ and denoted by $χ_2(G)$. In this paper, we will show that if $G$ is a regular graph, then $ χ_{2}(G)- χ(G) \leq 2 \log _{2}(α(G)) +\mathcal{O}(1) $ and if $G$ is a graph and $δ(G)\geq 2$, then $ χ_{2}(G)- χ(G) \leq 1+\lceil \sqrt[δ-1]{4Δ^{2}}…
Finding a directed acyclic graph (DAG) that best encodes the conditional independence statements observable from data is a central question within causality. Algorithms that greedily transform one candidate DAG into another given a fixed set of moves have been particularly successful, for example the GES, GIES, and MMHC algorithms. In 2010, Studený, Hemmecke and Lindner introduced the characteristic imset polytope, $\operatorname{CIM}_p$, whose vertices correspond to Markov equivalence classes, as a way of transforming causal discovery into a linear optimization problem. We show that the moves…
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