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1999, Information Processing Letters
Let Qn be the n-cube and let Qnk be the subgraph of Qn induced by the vertices at distance ≤k from a given vertex. Qnk-like graphs are introduced as graphs in which for any vertex u the set of vertices at distance ≤k from u induces a Qnk. Two characterizations of Qnk-like graphs are given and an O(d|V(G)|2) recognition algorithm is presented, where d is the degree of a given d-regular graph G. Several examples of Qnk-like graphs are also listed.
European Journal of Combinatorics
We fill in the details of the algorithm sketched in [6] and determine its complexity . As a part of this main algorithm , we also describe an algorithm which recognizes graphs which are isometric subgraphs of halved cubes . We discuss possible further applications of the same ideas and give a nice example of non-l 1 -graph allowing a highly isometric embedding into a halved cube .
Computers & Mathematics With Applications, 1988
Almtract--We present a comprehensive survey of the theory of hypercube graphs. Basic properties related to distance, coloring, domination and genus are reviewed. The properties of the n-cube defined by its subgraphs are considered next, including thickness, coarseness, Hamiltonian cycles and induced paths and cycles. Finally, various embedding and packing problems are discussed, including the determination of the cubical dimension of a given cubical graph.
Graphs are used in modeling interconnections networks and measuring their properties. Knowing and understanding the graph theoretical/combinatorial properties of the underlying networks are necessary in developing more efficient parallel algorithms as well as fault-tolerant communication/routing algorithms [1] The hypercube is one of the most versatile and efficient networks yet discovered for parallel computation. One generalization of the hypercube is the n-cube Q(n,m) which is a graph whose vertices are all the binary n-tuples, such that two vertices are adjacent whenever they differ in exactly m coordinates. The k-subgraph of the Generalized n-cube Q k (n,m) is the induced subgraph of the n-cube Q(n,m) where q=2, such that a vertex v ∈ V(Q k (n,m)) if and only if v ∈ V(Q(n,m)) and v is of parity k. This paper presents some degree properties of Q k (n,m) as well as some isomorphisms it has with other graphs, namely: 1)) 2 , (1 n Q n− is isomorphic to Kn 2)) 2 , (i n Q k is isomor...
European Journal of Combinatorics, 1996
We fill in the details of the algorithm sketched in [6] and determine its complexity . As a part of this main algorithm , we also describe an algorithm which recognizes graphs which are isometric subgraphs of halved cubes . We discuss possible further applications of the same ideas and give a nice example of non-l 1 -graph allowing a highly isometric embedding into a halved cube .
Journal of Graph Theory, 1999
A minimal detour subgraph of the n-dimensional cube is a spanning subgraph G of Q n having the property that, for vertices x, y of Q n , distances are related by d G (x, y) ≤ d Qn (x, y)+2. For a spanning subgraph G of Q n to be a local detour subgraph, we require only that the above inequality be satisfied whenever x and y are adjacent in Q n. Let f (n) (respectively, f l (n)) denote the minimum * Dedicated to the memory of Paul Erdős Contract grant sponsor: DIMACS. DIMACS is a cooperative
arXiv: Combinatorics, 2016
We study a family of graphs related to the n-cube. The middle cube graph of parameter k is the subgraph of Q 2k−1 induced by the set of vertices whose binary representation has either k − 1 or k number of ones. The middle cube graphs can be obtained from the wellknown odd graphs by doubling their vertex set. Here we study some of the properties of the middle cube graphs in the light of the theory of distance-regular graphs. In particular, we completely determine their spectra (eigenvalues and their multiplicities, and associated eigenvectors).
Discrete Mathematics, 2009
For integers n ≥ 1, k ≥ 0, and k ≤ n, the graph Γ k n has vertices the 2 n vectors of F n 2 and adjacency defined by two vectors being adjacent if they differ in k coordinate positions. In particular Γ 1 n is the n-cube, usually denoted by Q n. We examine the binary codes obtained from the adjacency matrices of these graphs when k = 1, 2, 3, following results obtained for the binary codes of the n-cube in Fish [6] and Key and Seneviratne [12]. We find the automorphism groups of the graphs and of their associated neighbourhood designs for k = 1, 2, 3, and the dimensions of the ternary codes for k = 1, 2. We also obtain 3-PD-sets for the self-dual binary codes from Γ 2 n when n ≡ 0 (mod 4), n ≥ 8.
Lecture Notes in Computer Science, 1996
Embeddings of several graph classes into hypercubes have been widely studied. Unfortunately, almost all investigated graph classes are regular graphs such as meshes, complete trees, pyramids. In this paper, we present a general method for one-to-one embedding irregular graphs into their optimal hypercubes based on extended-edge-bisectors of graphs. An extended-edge-bisector is an edge-bisector with the additional property that a subset of the vertices is distributed more or less evenly among the two halves of the bisected graph. The dilation and congestion of the embedding depends on the quality of the extended-edge-bisector. Moreover, if the extended bisection can be efficiently computed on the hypercube, so can the embedding.
Journal of Interconnection Networks, 2012
Graph embedding has been known as a powerful tool for implementation of parallel algorithms and simulation of interconnection networks. In this paper, we introduce a technique to obtain a lower bound for the dilation of an embedding. Moreover, we give algorithms for embedding variants of hypercubes with dilation 2 proving that the lower bound obtained is sharp. Further, we compute the exact wirelength of embedding folded hypercubes and augmented cubes into hypercubes. embedding is defined as the maximum distance between a pair of vertices of H that are images of adjacent vertices of G. It is a measure for the communication time needed when simulating one network on another. Another important cost criteria is the wirelength. The wirelength of a graph embedding arises from VLSI designs, data structures and data representations, networks for parallel computer systems, biological models that deal with cloning and visual stimuli, parallel architecture, structural engineering and so on. 3,4 Even though there are numerous results and discussions on the wirelength problem, most of them deal with only approximate results and the estimation of lower bounds. 5, Graph embeddings have been well studied for binary trees into paths, 4 binary trees into hypercubes, 2,7 complete binary trees into hypercubes, 8 incomplete hypercube in books, 9 tori and grids into twisted cubes, 10 meshes into locally twisted cubes, 11 meshes into faulty crossed cubes, 1 meshes into crossed cubes, 12 generalized ladders into hypercubes, 13 grids into grids, 14 binary trees into grids, 15 hypercubes into cycles, 6,16 star graph into path, 17 snarks into torus, 18 generalized wheels into arbitrary trees, 19 hypercubes into grids, 20 m-sequencial k -ary trees into hypercubes, 21 meshes into möbius cubes, 22 ternary trees into hypercubes, 23 enhanced and augmented hypercubes into complete binary trees, 24 circulant into arbitrary trees, cycles, certain multicyclic graphs and ladders, 25 hypercubes into cylinders, snakes and caterpillars, 26 hypercubes into necklace, windmill and snake graphs, 27 embedding of special classes of circulant networks hypercubes and generalized Petersen graphs. In recent years, among many interconnection networks, the hypercube has been the focus of many researchers due to its structural regularity, potential for parallel computation of various algorithms, and the high degree of fault tolerance. 29 Hypercubes are known to simulate other structures such as grids and binary trees. 7,20
A generalized hypercube graph $Q_n(S)$ has $F_2^n = {0,1}^n$ as the vertex set and two vertices being adjacent whenever their mutual Hamming distance belongs to $S$, where $n ≥ 1$ and $S ⊆ {1, 2, . . . , n}$. The graph $Q_n({1})$ is the $n-$cube, usually denoted by $Q_n$. We study graph boolean products $G_1 = Q_n(S) × Q_1, G_2 = Q_n(S) ∧ Q_1, G_3 = Q_n(S)[Q1]$ and show that binary codes from neighborhood designs of $G_1, G_2 and G_3$ are self-orthogonal for all choices of $n$ and $S$. More over, we show that the class of codes $C_1$ are self-dual. Further we find subgroups of the automorphism group of these graphs and use these subgroups to obtain PD-sets for permutation decoding. As an example we find a full error-correcting PD set for the binary [32, 16, 8] extremal self-dual code.
Electronic Notes in Discrete Mathematics, 2006
ABSTRACT Isometric subgraphs of hypercubes are known as partial cubes. These graphs have first been investigated by Graham and Pollak [R.L Graham, H.Pollak On the addressing problem for loop switching, Bell System Technol. J. 50 (1971) 2495–2519] and Djokovic̀ [D. Djokovic̀, Distance preserving subgraphs of the hypercubes, J. Combin. Theory, Ser B41 (1973), 263–267]. Several papers followed with various characterizations of partial cubes. In this paper, we determine all subdivisions of a given configuration which can be embedded isometrically in the hypercube. More specially, we deal with the case where this configuration is a connected graph of order 4 on one hand and the case where the configuration is a fan Fk(k⩾3) on the other hand. Finally, we conjecture that a subdivision of a complete graph of order n(n⩾5) is a partial cube if and only if this one is isomorphic to S(Kn) or there exists n−1 edges of Kn adjacent to a common vertex in the subdivision and the other edges of Kn contain odd added vertices. This proposition is true when the order n∈{4,5,6}.
Discussiones Mathematicae Graph Theory, 2003
Tree-like isometric subgraphs of hypercubes, or tree-like partial cubes as we shall call them, are a generalization of median graphs. Just as median graphs they capture numerous properties of trees, but may contain larger classes of graphs that may be easier to recognize than the class of median graphs. We investigate the structure of treelike partial cubes, characterize them, and provide examples of similarities with trees and median graphs. For instance, we show that the cube graph of a tree-like partial cube is dismantlable. This in particular implies that every tree-like partial cube G contains a cube that is invariant under every automorphism of G. We also show that weak retractions preserve tree-like partial cubes, which in turn implies that * Supported by the Ministry of Education, Science and Sport of Slovenia under the grants Z1-3073, and 0101-P-504, respectively. 228 B. Brešar, W. Imrich and S. Klavžar every contraction of a tree-like partial cube fixes a cube. The paper ends with several Frucht-type results and a list of open problems.
Discrete Mathematics, 2009
Isometric subgraphs of hypercubes are known as partial cubes. These graphs have first been investigated by Graham and Pollack [R.L. Graham, H. Pollack, On the addressing problem for loop switching, Bell System Technol. J. 50 (1971) 2495-2519; and D. Djoković, Distance preserving subgraphs of hypercubes, J. Combin. Theory Ser. B 14 (1973) 263-267]. Several papers followed with various characterizations of partial cubes. In this paper, we determine all subdivisions of a given configuration which can be embedded isometrically in the hypercube. More specifically, we deal with the case where this configuration is a connected graph of order 4, a complete graph of order 5 and the case of a k-fan F k (k ≥ 3).
Arxiv preprint math/0411359, 2004
A connected 3-valent plane graph, whose faces are q-or 6-gons only, is called a graph q n . We classify all graphs 4 n , which are isometric subgraphs of a m-hypercube H m .
AKCE International Journal of Graphs and Combinatorics, 2020
The n-dimensional augmented cube AQ n is a variation of the hypercube Q n : It is a ð2n À 1Þ-regular and ð2n À 1Þ-connected graph on 2 n vertices. One of the fundamental properties of AQ n is that it is pancyclic, that is, it contains a cycle of every length from 3 to 2 n : In this paper, we generalize this property to k-regular subgraphs for k ¼ 3 and k ¼ 4: We prove that the augmented cube AQ n with n ! 4 contains a 4-regular, 4-connected and pancyclic subgraph on l vertices if and only if 8 l 2 n : Also, we establish that for every even integer l from 4 to 2 n , there exists a 3-regular, 3-connected and pancyclic subgraph of AQ n on l vertices.
Ars Combinatoria - ARSCOM, 2004
Isometric subgraphs of hypercubes are known as partial cubes. Edge-critical partial cubes are introduced as the partial cubes G for which G?e is not a partial cube for any edge e of G. An expansion theorem is proved by means of which one can generate many edge-critical partial cubes. Edge-critical partial cubes are characterized among the Cartesian product graphs. We also show that the 3-cube and the subdivision graph of K 4 are the only edge-critical partial cubes on at most 10 vertices.
AUSTRALASIAN JOURNAL OF …, 2003
All cubic partial cubes (i.e., cubic isometric subgraphs of hypercubes) up to 30 vertices and all edge-critical partial cubes up to 14 vertices are presented. The lists of graphs were confirmed by computer search to be complete. Non-trivial cubic partial cubes on 36, 42, and 48 vertices are also constructed.
Algorithms and Combinatorics, 1997
The size sz(Γ) of an ℓ1-graph Γ = (V, E) is the minimum of n f /t f over all the possible ℓ1-embeddings f into n f-dimensional hypercube with scale t f. The sum of distances between all the pairs of vertices of Γ is at most sz(Γ)⌈v/2⌉⌊v/2⌋ (v = |V |). The latter is an equality if and only if Γ is equicut graph, that is, Γ admits an ℓ1-embedding f that for any 1 ≤ i ≤ n f satisfies x∈X f (x)i ∈ {⌈v/2⌉, ⌊v/2⌋} for any x ∈ V. Basic properties of equicut graphs are investigated. A construction of equicut graphs from ℓ1-graphs via a natural doubling construction is given. It generalizes several well-known constructions of polytopes and distanceregular graphs. Finally, large families of examples, mostly related to polytopes and distance-regular graphs, are presented.
Journal of Combinatorial Theory, Series A, 1988
Discrete Mathematics, 2003
Isometric subgraphs of hypercubes are known as partial cubes. The subdivision graph of a graph G is obtained from G by subdividing every edge of G. It is proved that for a connected graph G its subdivision graph is a partial cube if and only if every block of G is either a cycle or a complete graph. Regular partial cubes are also considered. In particular it is shown that among the generalized Petersen graphs P (10, 3) and P (2n, 1), n ≥ 2, are the only (regular) partial cubes.
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