Добірка наукової літератури з теми "Subcubic graph"

We present efficient algorithms for three coloring problems on subcubic graphs. (A subcubic graph has maximum degree at most three.) The first algorithm is for 4-edge coloring, or more generally, 4-list-edge coloring. Our algorithm runs in linear time, and appears to be simpler than previous ones. The second algorithm is the first randomized EREW PRAM algorithm for the same problem. It uses O(n/ log n) processors and runs in O( log n) time with high probability, where n is the number of vertices of the graph. The third algorithm is the first linear-time algorithm to 5-total-color subcubic graphs. The fourth algorithm generalizes this to get the first linear-time algorithm to 5-list-total-color subcubic graphs. Our sequential algorithms are based on a method of ordering the vertices and edges by traversing a spanning tree of a graph in a bottom-up fashion. Our parallel algorithm is based on a simple decomposition principle for subcubic graphs.

A (signed) graph is called Laplacian integral if all eigenvalues of its Laplacian matrix are integers. In this paper, we determine all connected Laplacian integral signed graphs of maximum degree 3; among these signed graphs,there are two classes of Laplacian integral signed graphs, one contains 4 infinite families of signed graphs and another contains 29 individual signed graphs.

We study strong list edge coloring of subcubic graphs, and we prove that every subcubic graph with maximum average degree less than 15/7, 27/11, 13/5, and 36/13 can be strongly list edge colored with six, seven, eight, and nine colors, respectively.

Let [Formula: see text] be a graph and [Formula: see text] be a positive integer. The [Formula: see text]-subdivision [Formula: see text] of [Formula: see text] is the graph obtained from [Formula: see text] by replacing each edge by a path of length [Formula: see text]. The [Formula: see text]-power [Formula: see text] of [Formula: see text] is the graph with vertex set [Formula: see text] in which two vertices [Formula: see text] and [Formula: see text] are adjacent if and only if the distance [Formula: see text] between [Formula: see text] and [Formula: see text] in [Formula: see text] is at most [Formula: see text]. Note that [Formula: see text] is the total graph [Formula: see text] of [Formula: see text]. The chromatic number [Formula: see text] of [Formula: see text] is the minimum integer [Formula: see text] for which [Formula: see text] has a proper [Formula: see text]-coloring. The total chromatic number of [Formula: see text], denoted by [Formula: see text], is the chromatic number of [Formula: see text]. Rosenfeld [On the total coloring of certain graphs, Israel J. Math. 9 (1971) 396–402] and independently, Vijayaditya [On total chromatic number of a graph, J. London Math. Soc. 2 (1971) 405–408] showed that for a subcubic graph [Formula: see text], [Formula: see text]. In this note, we prove that for a subcubic graph [Formula: see text], [Formula: see text].

It is proved that the median eigenvalues of every connected bipartite graph G of maximum degree at most three belong to the interval [−1, 1] with a single exception of the Heawood graph, whose median eigenvalues are $\pm\sqrt{2}$. Moreover, if G is not isomorphic to the Heawood graph, then a positive fraction of its median eigenvalues lie in the interval [−1, 1]. This surprising result has been motivated by the problem about HOMO-LUMO separation that arises in mathematical chemistry.

A strong[Formula: see text]-edge-coloring of a graph [Formula: see text] is a mapping [Formula: see text]: [Formula: see text], such that [Formula: see text] for every pair of distinct edges at distance at most two. The strong chromatical index of a graph [Formula: see text] is the least integer [Formula: see text] such that [Formula: see text] has a strong-[Formula: see text]-edge-coloring, denoted by [Formula: see text]. In this paper, we prove [Formula: see text] for any subcubic planar graph with [Formula: see text] and [Formula: see text]-cycles are not adjacent to [Formula: see text]-cycles.

A 2-distance vertex-distinguishing total coloring of graph G is a proper total coloring of G such that any pair of vertices at distance of two have distinct sets of colors. The 2-distance vertex-distinguishing total chromatic number $\chi_{d2}^{''}(G)$ of G is the minimum number of colors needed for a 2-distance vertex-distinguishing total coloring of G. In this paper, it's proved that if G is a subcubic graph, then $\chi_{d2}^{''}(G)\le 7$.

AbstractPfaffian graphs are those which can be oriented so that the 1-factors have equal sign, as calculated according to the prescription of Kasteleyn. We consider various operations on graphs and examine their effect on the Pfaffian property. We show that the study of Pfaffian graphs may be reduced to the case of subcubic graphs (graphs in which no vertex has degree greater than 3) or bricks (3-connected bicritical graphs).

Cette thèse de doctorat est divisée en deux parties principales: La partie I explore l'existence de chemins orientés dans les digraphes, cherchant à établir un lien entre le nombre chromatique d'un digraphe et l'existence de chemins orientés spécifiques en tant que sous-digraphes. Les digraphes contenus dans n'importe quel digraphe n-chromatique sont appelés n-universels. Nous examinons deux conjectures : la conjecture de Burr, qui affirme que chaque arbre orienté d'ordre n est (2n-2)-universel, et la conjecture d'El Sahili, qui déclare que chaque chemin orienté d'ordre n est n-universel. Pour les chemins orientés en général, la meilleure borne est donnée par Burr, à savoir que chaque chemin orienté d'ordre n est (n - 1)²-universel.Notre objectif est d'étudier des chemins à trois blocs. Pour atteindre nos objectifs, nous nous appuyons fortement sur des concepts fondamentaux, y compris l'induction sur l'ordre d'un digraphe donné, les forêts finales, les techniques de nivellement et les méthodes de décomposition stratégique de digraphes. Un chemin comportant trois blocs est désigné par P(k1, k2, k3). Pour le chemin P(k,1,l), nous avons confirmé la conjecture d'El Sahili dans les digraphes Hamiltoniens. En se basant sur ce résultat pour les digraphes Hamiltoniens, nous avons confirmé la conjecture d'El Sahili pour une classe plus générale de digraphes, ceux qui incluent un chemin dirigé hamiltonien. Nous introduisons une technique novatrice : une décomposition du digraphe en sous-digraphes résultant d'une série d'opérations basées sur le fameux théorème de Roy, qui garantit l'existence d'un chemin orienté dirigé d'ordre n dans tout digraphe n-chromatique. Cette technique s'est avérée cruciale pour établir de nouvelles bornes linéaires pour le nombre chromatique de digraphes qui ne comportent pas de chemin orienté avec trois blocs. En effet, en utilisant cette technique, nous avons prouvé que le chemin P(k,1,l) satisfait la conjecture de Burr. De plus, pour n'importe quel chemin à trois blocs, P(k,l,r), nous avons établi une borne linéaire pour le nombre chromatique qui améliore toutes les bornes précédemment atteintes. Dans la partie II, nous étudions le problème de la coloration de packing dans les graphes. Étant donnée une séquence non décroissante S = (s1, s2, . . . , sk) d'entiers positifs, une S-coloration (de packing) d'un graphe G est une partition de l'ensemble des sommets de G en k sous-ensembles {V1, V2, . . . , Vk} tels que pour chaque 1 ≤ i ≤ k, la distance entre deux sommets distincts u et v dans Vi est d'au moins si + 1. Notre attention est centrée sur une conjecture intrigante proposée par Brešar et al., qui affirme que l'arête subdivision de n'importe quel graphe subcubique admet une (1,2,3,4,5)-coloration de packing. Notre objectif est de confirmer cette conjecture pour des classes spécifiques de graphes subcubiques et de traiter les questions non résolues soulevées dans ce domaine. Une observation de Gastineau et Togni indique que si un graphe G est (1, 1, 2, 2)-colorable, alors son graphe subdivisé S(G) est (1,2,3,4,5)-colorable, et donc il satisfait la conjecture. En nous basant sur cette observation et afin de prouver la véracité de la conjecture pour la classe des graphes de Halin cubiques, nous avons étudié leur S-coloration de packing visant à prouver qu'ils admettent une coloration en (1, 1, 2, 2). Nous avons prouvé que tout graphe de Halin cubique est (1, 1, 2, 3)-colorable, et donc (1, 1, 2, 2)-colorable, et ainsi nous confirmons la conjecture pour cette classe. De plus, Gastineau et Togni, après avoir prouvé que chaque graphe subcubique est (1, 2, 2, 2, 2, 2, 2)-colorable, ont posé un problème ouvert sur le fait de savoir si chaque graphe subcubique est (1, 2, 2, 2, 2, 2)-colorable. Nous répondons affirmativement à cette question dans la classe particulière sur laquelle nous avons travaillé : nous avons prouvé que les graphes d'Halin cubiques sont (1, 2, 2, 2, 2, 2)-colorables
This PhD thesis is divided into two principal parts: Part I delves into the existenceof oriented paths in digraphs, aiming to establish a connection between a digraph'schromatic number and the existence of specific oriented paths within it as subdigraphs. Digraphs contained in any n-chromatic digraph are called n-universal. We consider two conjectures: Burr's conjecture, which states that every oriented tree of order n is (2n-2)-universal, and El Sahili's conjeture which states that every oriented path of order n is n-universal. For oriented paths in general, the best bound is given by Burr, that is every oriented path of order n is (n − 1)^2-universal. Our objective is to study the existence of an integer k such that any digraph with a chromatic number k, contains a copy of a given oriented path with three blocks as its subdigraph. To achieve our goals, we rely significantly on fundamental concepts, including, induction on the order of a given digraph, final forests, leveling techniques, and strategic digraph decomposition methods. A path P (k1, k2, k3) is an oriented path consisting of k1 forward arcs, followed by k2 backward arcs, and then by k3 forward arcs. For the path P(k,1,l), we have confirmed El Sahili's conjecture in Hamiltonian digraphs. More clearly, we have established the existence of any path P (k, 1, l) of order n in any n-chromatic Hamiltonian digraph. And depending on this result concerning Hamiltonian digraphs, we proved the correctness of El Sahili's conjecture on a more general class of digraphs which is digraphs containing a Hamiltonian directed path. We introduce a new technique which is represented by a decomposition of the digraph into subdigraphs defined by a series of successive operations applied to the digraph relying on the famous theorem of Roy which establishes the existence of a directed path of order n in any n-chromatic digraph. This technique has proven to be instrumental in establishing new linear bounds for the chromatic number of digraphs that lack an oriented path with three blocks. In deed, using this technique, we proved that the path P(k,1,l) satisfies Burr's conjecture.Moreover, for any path with three blocks, P(k,l,r) we establish a linear bound for the chromatic number which improves all the previously reached bounds. In Part II we study the problem of S-packing coloring in graphs. Given a non-decreasing sequence S = (s1, s2, . . . , sk) of positive integers, an S-packing coloring of a graph G is a partition of the vertex set of G into k subsets{V1, V2, . . . , Vk} such that for each 1 ≤ i ≤ k, the distance between any two dis-tinct vertices u and v in Vi is at least si + 1. Our focus is centered on an intriguing conjecture proposed by Brešar et al., which states that packing chromatic number of the subdivision of any subcubic graph is at most 5. Our desired aim is to provide a confirmation of this conjecture for specific classes of subcubic graphs, and to address the unresolved issues raised within this subject matter. An observation for Gastineau and Togni states that if a graph G is (1, 1, 2, 2)-packing colorable, then the chromatic number of its subdivision graph S(G) is at most 5, and hence it satisfies the conjecture. Depending on this observation, and in order to prove the correctness of the conjecture for the class of cubic Halin graphs, we studied its S-packing coloring aiming to prove that it admits a (1, 1, 2, 2)- packing coloring. We proved that a cubic Halin graph is (1, 1, 2, 3)-packing colorable, then it is (1, 1, 2, 2)-packing colorable, and so we confirm the conjecture for this class. Moreover, Gastineau and Togni, after proving that every subcubic graph is (1, 2, 2, 2, 2, 2, 2)-packing colorbale, have posed an open problem on whether every subcubic graph is (1, 2, 2, 2, 2, 2)-packing colorable. We answer this question in affirmative in the particular class we worked on; we proved that cubic Halin graphs are (1, 2, 2, 2, 2, 2)-packing colorable

This thesis focuses mainly on the Maximum Independent Set (MIS) problem. Some related graph theoretical combinatorial problems are also considered. As these problems are generally NP-hard, we study their complexity in hereditary graph classes, i.e. graph classes defined by a set F of forbidden induced subgraphs. We revise the literature about the issue, for example complexity results, applications, and techniques tackling the problem. Through considering some general approach, we exhibit several cases where the problem admits a polynomial-time solution. More specifically, we present polynomial-time algorithms for the MIS problem in: + some subclasses of $S_{2;j;k}$-free graphs (thus generalizing the classical result for $S_{1;2;k}$-free graphs); + some subclasses of $tree_{k}$-free graphs (thus generalizing the classical results for subclasses of P5-free graphs); + some subclasses of $P_{7}$-free graphs and $S_{2;2;2}$-free graphs; and various subclasses of graphs of bounded maximum degree, for example subcubic graphs. Our algorithms are based on various approaches. In particular, we characterize augmenting graphs in a subclass of $S_{2;k;k}$-free graphs and a subclass of $S_{2;2;5}$-free graphs. These characterizations are partly based on extensions of the concept of redundant set [125]. We also propose methods finding augmenting chains, an extension of the method in [99], and finding augmenting trees, an extension of the methods in [125]. We apply the augmenting vertex technique, originally used for $P_{5}$-free graphs or banner-free graphs, for some more general graph classes. We consider a general graph theoretical combinatorial problem, the so-called Maximum -Set problem. Two special cases of this problem, the so-called Maximum F-(Strongly) Independent Subgraph and Maximum F-Induced Subgraph, where F is a connected graph set, are considered. The complexity of the Maximum F-(Strongly) Independent Subgraph problem is revised and the NP-hardness of the Maximum F-Induced Subgraph problem is proved. We also extend the augmenting approach to apply it for the general Maximum Π -Set problem. We revise on classical graph transformations and give two unified views based on pseudo-boolean functions and αff-redundant vertex. We also make extensive uses of α-redundant vertices, originally mainly used for $P_{5}$-free graphs, to give polynomial solutions for some subclasses of $S_{2;2;2}$-free graphs and $tree_{k}$-free graphs. We consider some classical sequential greedy heuristic methods. We also combine classical algorithms with αff-redundant vertices to have new strategies of choosing the next vertex in greedy methods. Some aspects of the algorithms, for example forbidden induced subgraph sets and worst case results, are also considered. Finally, we restrict our attention on graphs of bounded maximum degree and subcubic graphs. Then by using some techniques, for example ff-redundant vertex, clique separator, and arguments based on distance, we general these results for some subclasses of $S_{i;j;k}$-free subcubic graphs.

A proper edge coloring of G =(V,E)is a map c : E → C (where C is the set of available colors ) with c(e) ≠ c(ƒ) for any adjacent edges e,f. The minimum number of colors needed to properly color the edges of G, is called the chromatic index of Gand is denoted by χ(G). A proper edge coloring c is called acyclic if there are no bichromatic cycles in the graph. In other words an edge coloring is acyclic if the union of any two color classes induces a set of paths (i.e., linear forest) in G. The acyclic edge chromatic number (also called acyclic chromatic index), denoted by a’(G), is the minimum number of colors required to acyclically edge color G. The primary motivation for this thesis is the following conjecture by Alon, Sudakov and Zaks [7] (and independently by Fiamcik [22]): Acyclic Edge Coloring Conjecture: For any graph G, a’ (G) ≤ Δ(G)+2. The following are the main results of the thesis: 1 From a result of Burnstein [16], it follows that any subcubic graph can be acyclically edge colored using at most 5 colors. Skulrattankulchai [38] gave a polynomial time algorithm to color a subcubic graph using Δ + 2 = 5 colors. We proved that any non-regular subcubic graph can be acyclically colored using only 4 colors. This result is tight. This also implies that the fifth color, when needed is required only for one edge. 2 Let G be a connected graph on n vertices, m ≤ 2n - 1 edges and maximum degree Δ ≤ 4, then a’ (G) ≤ 6. This implies that graph of maximum degree 4 are acyclically edge colorable using at most 7 colors. 3 The earliest result on acyclic edge coloring of 2-degenerate graphs was by Caro and Roditty [17], where they proved that a’ (G) ≤ Δ + k - 1, where k is the maximum edge connectivity, defined as k = maxu,vε V(G)λ(u,v), where λ(u,v)is the edge-connectivity of the pair u,v. Note that here k can be as high as Δ. Muthu,Narayanan and Subramanian [34] proved that a’ (G) ≤ Δ + 1for outerplanar graphs which are a subclass of 2-degenerate graphs and posed the problem of proving the conjecture for 2-degenerate graphs as an open problem. In fact they have also derived an upper bound of Δ+1 for series-parallel graphs [35], which is a slightly bigger subclass of 2-degenerate graphs. We proved that 2-degenerate graphs are Δ+1colorable. 1 Fiedorowicz, Hauszczak and Narayanan [24] gave an upper bound of 2Δ+29 for planar graphs. Independently Hou, Wu, GuiZhen Liu and Bin Liu [29] gave an upper bound of max(2Δ - 2,Δ+ 22). We improve this upper bound to Δ+12, which is the best known bound at present. 2 Fiedorowicz, Hauszczak and Narayanan [24] gave an upper bound of Δ+6for triangle free planar graphs. We improve the bound to Δ+3, which is the best known bound at present. 3 We have also worked on lower bounds. Alon et.al. [7], along with the acyclic edge coloring conjecture, also made an auxiliary conjecture stating that Complete graphs of 2n vertices are the only class of regular graphs which require Δ+2colors. We disproved this conjecture by showing infinite classes of regular graphs other than Complete Graphs which require Δ+2colors. Apart from the above mentioned results, this thesis also contributes to the acyclic edge coloring literature by introducing new techniques like Recoloring, Color Exchange (exchanging colors of adjacent edges), circular shifting of colors on adjacent edges (derangement of colors). These techniques turn out to be very useful in proving upper bounds on the acyclic edge chromatic number.

A proper edge coloring of G =(V,E)is a map c : E → C (where C is the set of available colors ) with c(e) ≠ c(ƒ) for any adjacent edges e,f. The minimum number of colors needed to properly color the edges of G, is called the chromatic index of Gand is denoted by χ(G). A proper edge coloring c is called acyclic if there are no bichromatic cycles in the graph. In other words an edge coloring is acyclic if the union of any two color classes induces a set of paths (i.e., linear forest) in G. The acyclic edge chromatic number (also called acyclic chromatic index), denoted by a’(G), is the minimum number of colors required to acyclically edge color G. The primary motivation for this thesis is the following conjecture by Alon, Sudakov and Zaks [7] (and independently by Fiamcik [22]): Acyclic Edge Coloring Conjecture: For any graph G, a’ (G) ≤ Δ(G)+2. The following are the main results of the thesis: 1 From a result of Burnstein [16], it follows that any subcubic graph can be acyclically edge colored using at most 5 colors. Skulrattankulchai [38] gave a polynomial time algorithm to color a subcubic graph using Δ + 2 = 5 colors. We proved that any non-regular subcubic graph can be acyclically colored using only 4 colors. This result is tight. This also implies that the fifth color, when needed is required only for one edge. 2 Let G be a connected graph on n vertices, m ≤ 2n - 1 edges and maximum degree Δ ≤ 4, then a’ (G) ≤ 6. This implies that graph of maximum degree 4 are acyclically edge colorable using at most 7 colors. 3 The earliest result on acyclic edge coloring of 2-degenerate graphs was by Caro and Roditty [17], where they proved that a’ (G) ≤ Δ + k - 1, where k is the maximum edge connectivity, defined as k = maxu,vε V(G)λ(u,v), where λ(u,v)is the edge-connectivity of the pair u,v. Note that here k can be as high as Δ. Muthu,Narayanan and Subramanian [34] proved that a’ (G) ≤ Δ + 1for outerplanar graphs which are a subclass of 2-degenerate graphs and posed the problem of proving the conjecture for 2-degenerate graphs as an open problem. In fact they have also derived an upper bound of Δ+1 for series-parallel graphs [35], which is a slightly bigger subclass of 2-degenerate graphs. We proved that 2-degenerate graphs are Δ+1colorable. 1 Fiedorowicz, Hauszczak and Narayanan [24] gave an upper bound of 2Δ+29 for planar graphs. Independently Hou, Wu, GuiZhen Liu and Bin Liu [29] gave an upper bound of max(2Δ - 2,Δ+ 22). We improve this upper bound to Δ+12, which is the best known bound at present. 2 Fiedorowicz, Hauszczak and Narayanan [24] gave an upper bound of Δ+6for triangle free planar graphs. We improve the bound to Δ+3, which is the best known bound at present. 3 We have also worked on lower bounds. Alon et.al. [7], along with the acyclic edge coloring conjecture, also made an auxiliary conjecture stating that Complete graphs of 2n vertices are the only class of regular graphs which require Δ+2colors. We disproved this conjecture by showing infinite classes of regular graphs other than Complete Graphs which require Δ+2colors. Apart from the above mentioned results, this thesis also contributes to the acyclic edge coloring literature by introducing new techniques like Recoloring, Color Exchange (exchanging colors of adjacent edges), circular shifting of colors on adjacent edges (derangement of colors). These techniques turn out to be very useful in proving upper bounds on the acyclic edge chromatic number.

碩士
國立中山大學
應用數學系研究所
96
Suppose G is a graph with n vertices and m edges. Let n′ be the maximum number of vertices in an induced bipartite subgraph of G and let m′ be the maximum number of edges in a spanning bipartite subgraph of G. Then b(G) = m′/m is called the bipartite density of G, and b∗(G) = n′/n is called the bipartite ratio of G. It is proved in [18] that if G is a 2-connected triangle-free subcubic graph, then apart from seven exceptional graphs, we have b(G) ≥ 17/21. If G is a 2-connected triangle-free subcubic graph, then b∗(G) ≥ 5/7 provided that G is not the Petersen graph and not the dodecahedron. These two results are consequences of a more technical result which is proved by induction: If G is a 2-connected triangle-free subcubic graph with minimum degree 2, then G has an induced bipartite subgraph H with |V (H)| ≥ (5n3 + 6n2 + ǫ(G))/7, where ni = ni(G) are the number of degree i vertices of G, and ǫ(G) ∈ {−2,−1, 0, 1}. To determine ǫ(G), four classes of graphs G1, G2, G3 and F-cycles are onstructed. For G ∈ Gi, we have ǫ(G) = −3 + i and for an F-cycle G, we have ǫ(G) = 0. Otherwise, ǫ(G) = 1. To construct these graph classes, eleven graph operations are used. This thesis studies the structural property of graphs in G1, G2, G3. First of all, a computer algorithm is used to generate all the graphs in Gi for i = 1, 2, 3. Let P be the set of 2-edge connected subcubic triangle-free planar graphs with minimum degree 2. Let G′ 1 be the set of graphs in P with all faces of degree 5, G′2 the set of graphs in P with all faces of degree 5 except that one face has degree 7, and G′3 the set of graphs in P with all faces of degree 5 except that either two faces are of degree 7 or one face is of degree 9. By checking the graphs generated by the computer algorithm, it is easy to see that Gi ⊆ G′i for i = 1, 2, 3. The main results of this thesis are that for i = 1, 2, Gi = G′i and G′3 = G3 ∪R, where R is a set of nine F-cycles.

碩士
國立清華大學
資訊系統與應用研究所
104
A total vertex cover is a vertex cover whose induced subgraph consists of a set of connected components, each of which contains at least two vertices. A t-total vertex cover is a total vertex cover where each component of its induced subgraph contains at least t vertices. The total vertex cover (TVC) problem and the t-total vertex cover (t-TVC) problem ask for the corresponding cover set with minimum cardinality, respectively. In this paper, we first show that the t-TVC problem is NP-complete for connected subcubic grid graphs of arbitrary large girth. Next, we show that the t-TVC problem is NP-complete for 3-connected cubic planar graphs. Moreover, we show that the t-TVC problem is APX-complete for connected subcubic graphs of arbitrary large girth.

This thesis focuses mainly on the Maximum Independent Set (MIS) problem. Some related graph theoretical combinatorial problems are also considered. As these problems are generally NP-hard, we study their complexity in hereditary graph classes, i.e. graph classes defined by a set F of forbidden induced subgraphs. We revise the literature about the issue, for example complexity results, applications, and techniques tackling the problem. Through considering some general approach, we exhibit several cases where the problem admits a polynomial-time solution. More specifically, we present polynomial-time algorithms for the MIS problem in: + some subclasses of $S_{2;j;k}$-free graphs (thus generalizing the classical result for $S_{1;2;k}$-free graphs); + some subclasses of $tree_{k}$-free graphs (thus generalizing the classical results for subclasses of P5-free graphs); + some subclasses of $P_{7}$-free graphs and $S_{2;2;2}$-free graphs; and various subclasses of graphs of bounded maximum degree, for example subcubic graphs. Our algorithms are based on various approaches. In particular, we characterize augmenting graphs in a subclass of $S_{2;k;k}$-free graphs and a subclass of $S_{2;2;5}$-free graphs. These characterizations are partly based on extensions of the concept of redundant set [125]. We also propose methods finding augmenting chains, an extension of the method in [99], and finding augmenting trees, an extension of the methods in [125]. We apply the augmenting vertex technique, originally used for $P_{5}$-free graphs or banner-free graphs, for some more general graph classes. We consider a general graph theoretical combinatorial problem, the so-called Maximum -Set problem. Two special cases of this problem, the so-called Maximum F-(Strongly) Independent Subgraph and Maximum F-Induced Subgraph, where F is a connected graph set, are considered. The complexity of the Maximum F-(Strongly) Independent Subgraph problem is revised and the NP-hardness of the Maximum F-Induced Subgraph problem is proved. We also extend the augmenting approach to apply it for the general Maximum Π -Set problem. We revise on classical graph transformations and give two unified views based on pseudo-boolean functions and αff-redundant vertex. We also make extensive uses of α-redundant vertices, originally mainly used for $P_{5}$-free graphs, to give polynomial solutions for some subclasses of $S_{2;2;2}$-free graphs and $tree_{k}$-free graphs. We consider some classical sequential greedy heuristic methods. We also combine classical algorithms with αff-redundant vertices to have new strategies of choosing the next vertex in greedy methods. Some aspects of the algorithms, for example forbidden induced subgraph sets and worst case results, are also considered. Finally, we restrict our attention on graphs of bounded maximum degree and subcubic graphs. Then by using some techniques, for example ff-redundant vertex, clique separator, and arguments based on distance, we general these results for some subclasses of $S_{i;j;k}$-free subcubic graphs.

In 1988, Chetwynd and Hilton defined conformable vertex colorings when trying to characterize the vertex colorings induced by a (∆ + 1)-total coloring. Anticonformable colorings were used to characterize the subcubic conformable graphs. A graph G is anticonformable if it has a (∆ + 1)-vertex coloring such that the number of color classes (including empty color classes) with the same parity as |V| is at most def(G) = ∑v∈V (∆− dG(v)). The only connected subcubic not anticonformable graph is the triangular prism graph L3. In this paper, we prove that if k is even, then every k-regular graph is not anticonformable; and if k ≥ 3 is odd, then there is a not anticonformable graph Hk, where H3 = L3.

A graph is locally irregular if any pair of adjacent vertices have distinct degrees. A locally irregular decomposition of a graph G is a decomposition of G into subgraphs that are locally irregular. We prove that any graph G can be decomposed into at most 2∆(G) − 1 locally irregular graphs, improving on the previous upper bound of 3∆(G)−2. We also show some results on subcubic and non-decomposable graphs.

Given a simple graph G, an ordered pair (π, cπ) is said to be a gap- [k]-edge-labelling (resp. gap-[k]-vertex-labelling) ofG ifπ is an edge-labelling (vertex-labelling) on the set {1, . . . , k}, and cπ is a proper vertex-colouring such that every vertex of degree at least two has its colour induced by the largest difference among the labels of its incident edges (neighbours). The decision problems associated with these labellings are NP-complete for k ≥ 3, and even when k = 2 for some classes of graphs. This thesis presents a study of the computational complexity of these problems, structural properties for certain families of graphs and several labelling algorithms and techniques. First, we present an NP-completeness result for the family of subcubic bipartite graphs. Second, we present polynomial-time algorithms for families ofgraphs. Third, we introduce a new parameter associated with gap-[k]-vertex-labellings ofgraphs.

In this paper, we propose a hyperspectral band selection method via spatial-spectral weighted region-wise multiple graph fusion-based spectral clustering, referred to as RMGF briefly. Considering that different objects have different reflection characteristics, we use a superpixel segmentation algorithm to segment the first principal component of original hyperspectral image cube into homogeneous regions. For each superpixel, we construct a corresponding similarity graph to reflect the similarity between band pairs. Then, a multiple graph diffusion strategy with theoretical convergence guarantee is designed to learn a unified graph for partitioning the whole hyperspectral cube into several subcubes via spectral clustering. During the graph diffusion process, the spatial and spectral information of each superpixel are embedded to make spatial/spectral similar superpixels contribute more to each other. Finally, the band containing minimum noise in each subcube is selected to represent the whole subcube. Extensive experiments are conducted on three public datasets to validate the superiority of the proposed method when compared with other state-of-the-art ones.