130 results on '"Adjacency matrix"'
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2. On the number of minimal codewords in codes generated by the adjacency matrix of a graph
- Author
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Sascha Kurz
- Subjects
graphs ,Applied Mathematics ,minimal codewords ,TheoryofComputation_GENERAL ,Data_CODINGANDINFORMATIONTHEORY ,linear codes ,FOS: Mathematics ,Mathematics - Combinatorics ,Discrete Mathematics and Combinatorics ,Combinatorics (math.CO) ,Hardware_ARITHMETICANDLOGICSTRUCTURES ,Computer Science::Information Theory - Abstract
Minimal codewords have applications in decoding linear codes and in cryptography. We study the number of minimal codewords in binary linear codes that arise by appending a unit matrix to the adjacency matrix of a graph., Comment: 11 pages
- Published
- 2022
3. On the structure of the adjacency matrix of the line digraph of a regular digraph
- Author
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Severini, Simone
- Subjects
- *
UNIVERSAL algebra , *MATRICES (Mathematics) , *COMPLEX matrices , *TENSOR products - Abstract
Abstract: We show that the adjacency matrix M of the line digraph of a d-regular digraph D on n vertices can be written as , where the matrix A is the Kronecker product of the all-ones matrix of dimension d with the identity matrix of dimension n and the matrix B is the direct sum of the adjacency matrices of the factors in a dicycle factorization of D. [Copyright &y& Elsevier]
- Published
- 2006
- Full Text
- View/download PDF
4. On the characteristic polynomial of the adjacency matrix of the subdivision graph of a graph
- Author
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Shoji Shinoda
- Subjects
Discrete mathematics ,Spectral graph theory ,Applied Mathematics ,MathematicsofComputing_NUMERICALANALYSIS ,Distance-regular graph ,Combinatorics ,Graph energy ,Graph power ,TheoryofComputation_ANALYSISOFALGORITHMSANDPROBLEMCOMPLEXITY ,Seidel adjacency matrix ,ComputingMethodologies_SYMBOLICANDALGEBRAICMANIPULATION ,Discrete Mathematics and Combinatorics ,Adjacency list ,Regular graph ,Adjacency matrix ,MathematicsofComputing_DISCRETEMATHEMATICS ,Mathematics - Abstract
The characteristic polynomial of the adjacency matrix of the subdivision graph G is related to the characteristic polynomials of the adjacency matrices of g and its line graph.
- Full Text
- View/download PDF
5. Perfect state transfer in NEPS of complete graphs
- Author
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Sanming Zhou, Yipeng Li, Xiaogang Liu, and Shenggui Zhang
- Subjects
Vertex (graph theory) ,Applied Mathematics ,Diagonal ,0211 other engineering and technologies ,Stochastic matrix ,021107 urban & regional planning ,0102 computer and information sciences ,02 engineering and technology ,01 natural sciences ,Graph ,Moduli ,Combinatorics ,010201 computation theory & mathematics ,Discrete Mathematics and Combinatorics ,Adjacency matrix ,Perfect state transfer ,Mathematics ,Quantum computer - Abstract
Perfect state transfer in graphs is a concept arising from quantum physics and quantum computing. Given a graph G with adjacency matrix A G , the transition matrix of G with respect to A G is defined as H A G ( t ) = exp ( − i t A G ) , t ∈ R , i = − 1 . We say that perfect state transfer from vertex u to vertex v occurs in G at time τ if u ≠ v and the modulus of the ( u , v ) -entry of H A G ( τ ) is equal to 1. If the moduli of all diagonal entries of H A G ( τ ) are equal to 1 for some τ , then G is called periodic with period τ . In this paper we give a few sufficient conditions for NEPS of complete graphs to be periodic or exhibit perfect state transfer.
- Published
- 2021
6. Null decomposition of unicyclic graphs
- Author
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L. Emilio Allem, Daniel A. Jaume, Gonzalo Molina, Maikon Machado Toledo, and Vilmar Trevisan
- Subjects
Combinatorics ,Applied Mathematics ,Unicyclic graphs ,Discrete Mathematics and Combinatorics ,Adjacency matrix ,Graph ,MathematicsofComputing_DISCRETEMATHEMATICS ,Mathematics - Abstract
We find a basis for the null space of the adjacency matrix of unicyclic graphs. Based on the support of such a basis, we determine a null decomposition of these graphs. As an application, we obtain closed formulas for the independence and matching numbers of unicyclic graphs that solely rely on the support of the graph.
- Published
- 2020
7. Net Laplacian controllability for joins of signed graphs
- Author
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Zoran Stanić
- Subjects
Threshold graph ,Applied Mathematics ,0211 other engineering and technologies ,021107 urban & regional planning ,0102 computer and information sciences ,02 engineering and technology ,Net (mathematics) ,01 natural sciences ,Combinatorics ,010201 computation theory & mathematics ,Diagonal matrix ,Discrete Mathematics and Combinatorics ,Adjacency matrix ,Laplacian matrix ,Signed graph ,Laplace operator ,Eigenvalues and eigenvectors ,Mathematics - Abstract
The net Laplacian matrix of a signed graph G is defined to be N G = D G ± − A G , where D G ± and A G are the diagonal matrix of net-degrees and the adjacency matrix of G , respectively. For a binary vector b , the pair ( N G , b ) is controllable if N G has no eigenvector orthogonal to b ; we also say that G is net Laplacian controllable for b . In this study we consider the net Laplacian controllability of joins of signed graphs. In particular, we establish all controllable pairs ( N G , b ) , where G is a signed threshold graph determined by a ( 0 , 1 , − 1 ) -generating sequence. This result contains all controllable pairs ( L G , b ) , where L G is the Laplacian matrix of a graph G .
- Published
- 2020
8. A method for computing local contributions to graph energy based on Estrada–Benzi approach
- Author
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F. Kashkooei Jahromi, S. Fathi, and Farshad Safaei
- Subjects
Applied Mathematics ,0211 other engineering and technologies ,Diamond graph ,021107 urban & regional planning ,0102 computer and information sciences ,02 engineering and technology ,01 natural sciences ,Upper and lower bounds ,Graph ,Combinatorics ,Graph energy ,010201 computation theory & mathematics ,Discrete Mathematics and Combinatorics ,Path graph ,Adjacency matrix ,Total energy ,Graph property ,MathematicsofComputing_DISCRETEMATHEMATICS ,Mathematics - Abstract
The graph energy, as a graph invariant, contains very important structural information about the graph, its subgraphs, and ingredient segments. Estrada and Benzi (2017) have shown that the graph energy can be extracted from the weighted sum of the traces of the even powers of its adjacency matrix. Based on this kind of representation, they have reported newer and more precise bounds of the energy as the sum of fragments’ contributions such as C n (cycles of length n), P n (path graph), S n (star graph), D n (diamond graph), F (a subgraph containing a square with a pendant vertex), and H (a subgraph containing two triangles with a shared vertex). In this paper, inspired by the work of Estrada and Benzi, we first introduce a general formula for calculating the contribution of subgraphs to the total energy of the graph. We also compute the boundaries of the contributions of the above subgraphs and some of the subgraphs that appear for the first time in the higher traces of the adjacency matrix of the graph. Further, we calculate the upper bound of the graph energy for cyclic and fullerene graphs with higher accuracy.
- Published
- 2019
9. On hyper-Hamiltonicity in graphs
- Author
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Cybele T. M. Vinagre, Guilherme B. Pereira, and Renata R. Del-Vecchio
- Subjects
Vertex (graph theory) ,Threshold graph ,Applied Mathematics ,0211 other engineering and technologies ,021107 urban & regional planning ,0102 computer and information sciences ,02 engineering and technology ,Mathematics::Spectral Theory ,01 natural sciences ,Hamiltonian path ,Graph ,Combinatorics ,symbols.namesake ,Distance matrix ,010201 computation theory & mathematics ,symbols ,Discrete Mathematics and Combinatorics ,Adjacency matrix ,Laplacian matrix ,Eigenvalues and eigenvectors ,Mathematics - Abstract
A Hamiltonian graph G is said to be hyper-Hamiltonian when G − v is Hamiltonian for any vertex v of G . In this paper, sufficient conditions for a graph to be hyper-Hamiltonian based on different parameters, such as degree and number of edges, are presented. Furthermore, other sufficient conditions for hyper-Hamiltonicity are obtained from spectral parameters, such as the spectral radii of the adjacency matrix, the signless Laplacian matrix and the distance matrix. Results on hyper-Hamiltonicity of a threshold graph through the eigenvalues of its Laplacian matrix are also presented.
- Published
- 2020
10. The leaf-free graphs with nullity 2c(G)−1
- Author
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Sarula Chang, An Chang, and Yirong Zheng
- Subjects
Combinatorics ,Connected component ,Simple graph ,Applied Mathematics ,Discrete Mathematics and Combinatorics ,Multiplicity (mathematics) ,Adjacency matrix ,Disjoint sets ,Upper and lower bounds ,Graph ,Eigenvalues and eigenvectors ,Mathematics - Abstract
Let G be a simple graph with n ( G ) vertices and e ( G ) edges. The elementary cyclic number c ( G ) of G is defined as c ( G ) = e ( G ) − n ( G ) + ω ( G ) , where ω ( G ) is the number of connected components of G . The nullity of G , denoted by η ( G ) , is the multiplicity of the eigenvalue zero of the adjacency matrix of G . A graph is leaf-free if it has no pendent vertices. In Ma et al. (2016) proved that if G is leaf-free and each component of G contains at least two vertices, then η ( G ) ≤ 2 c ( G ) , the equality is attained if and only if G is the union of disjoint cycles, where each cycle has length a multiple of 4. In this paper, we completely characterize all leaf-free graphs with nullity one less than the above upper bound, i.e., η ( G ) = 2 c ( G ) − 1 .
- Published
- 2020
11. A class of spectral bounds for Max [formula omitted]-Cut.
- Author
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Anjos, Miguel F. and Neto, José
- Subjects
- *
CUTTING stock problem , *EIGENVALUES - Abstract
In this paper we introduce a new class of bounds for the maximum k -cut problem on undirected edge-weighted simple graphs. The bounds involve eigenvalues of the weighted adjacency matrix together with geometrical parameters. They generalize previous results on the maximum (2-)cut problem and we demonstrate that they can strictly improve over other eigenvalue bounds from the literature. We also report computational results illustrating the potential impact of the new bounds. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
12. Eigenvalue location in cographs
- Author
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Fernando Tura, David P. Jacobs, and Vilmar Trevisan
- Subjects
media_common.quotation_subject ,0211 other engineering and technologies ,0102 computer and information sciences ,02 engineering and technology ,Computer Science::Computational Complexity ,Inertia ,01 natural sciences ,Combinatorics ,Integer ,Computer Science::Discrete Mathematics ,Diagonal matrix ,FOS: Mathematics ,Mathematics - Combinatorics ,05C50, 05C85, 15A18 ,Discrete Mathematics and Combinatorics ,Cograph ,Adjacency matrix ,Computer Science::Data Structures and Algorithms ,Eigenvalues and eigenvectors ,media_common ,Mathematics ,Discrete mathematics ,Mathematics::Combinatorics ,Spacetime ,Applied Mathematics ,021107 urban & regional planning ,010201 computation theory & mathematics ,Interval (graph theory) ,Combinatorics (math.CO) - Abstract
We give an O ( n ) time and space algorithm for constructing a diagonal matrix congruent to A + x I , where A is the adjacency matrix of a cograph and x ∈ R . Applications include determining the number of eigenvalues of a cograph’s adjacency matrix that lie in any interval, obtaining a formula for the inertia of a cograph, and exhibiting infinitely many pairs of equienergetic cographs with integer energy.
- Published
- 2018
13. Eigenvector-based identification of bipartite subgraphs
- Author
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Dragan Stevanović and Debdas Paul
- Subjects
Random graph ,Applied Mathematics ,MathematicsofComputing_NUMERICALANALYSIS ,Complex network ,Mathematics - Spectral Theory ,Combinatorics ,FOS: Mathematics ,Bipartite graph ,Discrete Mathematics and Combinatorics ,Adjacency list ,Adjacency matrix ,Laplacian matrix ,Spectral Theory (math.SP) ,Laplace operator ,Eigenvalues and eigenvectors ,MathematicsofComputing_DISCRETEMATHEMATICS ,Mathematics - Abstract
We report our experiments in identifying large bipartite subgraphs of simple connected graphs which are based on the sign pattern of eigenvectors belonging to the extremal eigenvalues of different graph matrices: adjacency, signless Laplacian, Laplacian, and normalized Laplacian matrix. We compare the performance of these methods to a local switching algorithm based on the Erdos bound that each graph contains a bipartite subgraph with at least half of its edges. Experiments with one scale-free and three random graph models, which cover a wide range of real-world networks, show that the methods based on the eigenvectors of the normalized Laplacian and the adjacency matrix yield slightly better, but comparable results to the local switching algorithm. We also formulate two edge bipartivity indices based on the former eigenvectors, and observe that the method of iterative removal of edges with maximum bipartivity index until one obtains a bipartite subgraph, yields comparable results to the local switching algorithm, and significantly better results than an analogous method that employs the edge bipartivity index of Estrada and Gomez-Gardenes., 20 pages, 8 figures
- Published
- 2019
14. Bounds for the energy of weighted graphs
- Author
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Hilal A. Ganie and Bilal A. Chat
- Subjects
Applied Mathematics ,0211 other engineering and technologies ,021107 urban & regional planning ,0102 computer and information sciences ,02 engineering and technology ,Covering number ,01 natural sciences ,Graph ,Vertex (geometry) ,Combinatorics ,Graph energy ,010201 computation theory & mathematics ,Discrete Mathematics and Combinatorics ,Adjacency list ,Adjacency matrix ,Eigenvalues and eigenvectors ,Connectivity ,Mathematics - Abstract
Let G be a simple connected graph with n vertices and m edges. Let W ( G ) = ( G , w ) be the weighted graph corresponding to G . Let λ 1 , λ 2 , … , λ n be the eigenvalues of the adjacency matrix A ( W ( G ) ) of the weighted graph W ( G ) . The energy E ( W ( G ) ) of a weighted graph W ( G ) is defined as the sum of absolute value of the eigenvalues of W ( G ) . In this paper, we obtain upper bounds for the energy E ( W ( G ) ) , in terms of the sum of the squares of weights of the edges, the maximum weight, the maximum degree d 1 , the second maximum degree d 2 and the vertex covering number τ of the underlying graph G . As applications to these upper bounds we obtain some upper bounds for the energy (adjacency energy), the extended graph energy, the Randic energy and the signed energy of the connected graph G . We also obtain some new families of weighted graphs where the energy increases with increase in weights of the edges.
- Published
- 2019
15. The graphs cospectral with the pineapple graph
- Author
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Sezer Sorgun, Hatice Topcu, Willem H. Haemers, and Econometrics and Operations Research
- Subjects
Vertex (graph theory) ,adjacency matrix ,Applied Mathematics ,Complete graph ,spectral characterization ,Graph ,Combinatorics ,cospectral graphs ,Discrete Mathematics and Combinatorics ,Adjacency list ,Adjacency matrix ,pineapple graph ,Eigenvalues and eigenvectors ,Mathematics - Abstract
The pineapple graph K p q is obtained by appending q pendant edges to a vertex of a complete graph K p ( p ≥ 3 , q ≥ 1 ). We prove that among connected graphs, the pineapple graph is determined by its adjacency spectrum. Moreover, we determine all disconnected graphs which are cospectral with a pineapple graph. Thus we find for which values of p and q the pineapple graph K p q is determined by its adjacency spectrum. The main tool is a recent classification of all graphs with all but three eigenvalues equal to 0 or − 1 by the third author.
- Published
- 2019
16. Vertex types in threshold and chain graphs
- Author
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Ebrahim Ghorbani, Slobodan K. Simić, and Milica Anđelić
- Subjects
Threshold graph ,Conjecture ,Applied Mathematics ,0211 other engineering and technologies ,021107 urban & regional planning ,Multiplicity (mathematics) ,0102 computer and information sciences ,02 engineering and technology ,01 natural sciences ,Graph ,Vertex (geometry) ,Combinatorics ,010201 computation theory & mathematics ,FOS: Mathematics ,Bipartite graph ,Mathematics - Combinatorics ,Discrete Mathematics and Combinatorics ,Combinatorics (math.CO) ,Adjacency matrix ,05C50 ,Eigenvalues and eigenvectors ,Mathematics - Abstract
A graph is called a chain graph if it is bipartite and the neighbourhoods of the vertices in each colour class form a chain with respect to inclusion. A threshold graph can be obtained from a chain graph by making adjacent all pairs of vertices in one colour class. Given a graph G , let λ be an eigenvalue (of the adjacency matrix) of G with multiplicity k ≥ 1 . A vertex v of G is a downer, or neutral, or Parter depending whether the multiplicity of λ in G − v is k − 1 , or k , or k + 1 , respectively. We consider vertex types in the above sense in threshold and chain graphs. In particular, we show that chain graphs can have neutral vertices, disproving a conjecture by Alazemi et al.
- Published
- 2019
17. Edge construction of molecular NSSDs
- Author
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Alexander Farrugia
- Subjects
Applied Mathematics ,Weight change ,0211 other engineering and technologies ,021107 urban & regional planning ,0102 computer and information sciences ,02 engineering and technology ,01 natural sciences ,Graph ,law.invention ,Combinatorics ,chemistry.chemical_compound ,Invertible matrix ,chemistry ,010201 computation theory & mathematics ,law ,Discrete Mathematics and Combinatorics ,Molecular graph ,Adjacency matrix ,Mathematics - Abstract
A nonsingular graph with a singular deck, or NSSD, is a graph with weighted edges and no loops whose adjacency matrix is nonsingular and whose vertex-deleted subgraphs have singular adjacency matrices. When all the weights of the edges of a NSSD are equal to one, we obtain a molecular NSSD, which is an ipso omni-insulator molecular graph. We present necessary and sufficient conditions for a NSSD G to remain a NSSD after increasing the weight of one of its edges by w ∈ R ∖ { 0 } ; this weight change may result in the addition or removal of that edge to or from G . Using this result, we construct molecular NSSDs of a fixed even order. This is accomplished by systematically introducing edges to, or removing edges from, a nonsingular tree.
- Published
- 2019
18. New inequalities for network distance measures by using graph spectra
- Author
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Matthias Dehmer, Stefan Pickl, Guihai Yu, and Yongtang Shi
- Subjects
Discrete mathematics ,Degree matrix ,Resistance distance ,Spectral graph theory ,Applied Mathematics ,020206 networking & telecommunications ,02 engineering and technology ,Mathematics::Spectral Theory ,Combinatorics ,Integer matrix ,Graph energy ,Distance matrix ,0202 electrical engineering, electronic engineering, information engineering ,Discrete Mathematics and Combinatorics ,020201 artificial intelligence & image processing ,Adjacency matrix ,Laplacian matrix ,Mathematics - Abstract
Eigenvalues of graph-theoretical matrices often reflect structure properties of networks (graphs) meaningfully. In this paper, we explore inequalities for graph distance measures which are based on topological indices. Some of these indices are based on eigenvalues of graph-theoretical matrices. We here consider the adjacency matrix, the Laplacian matrix and signless Laplacian matrix. Besides proving the inequalities, we discuss the usefulness of these measures and state some conjectures.
- Published
- 2019
19. On the characteristic polynomial of the adjacency matrix of the subdivision graph of a graph
- Author
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Shinoda, Shoji, primary
- Published
- 1980
- Full Text
- View/download PDF
20. Spectral bounds for graph partitioning with prescribed partition sizes.
- Author
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Anjos, Miguel F. and Neto, José
- Subjects
- *
CUTTING stock problem , *EIGENVECTORS , *SEMIDEFINITE programming - Abstract
Given an undirected edge weighted graph, the graph partitioning problem consists in determining a partition of the node set of the graph into subsets of prescribed sizes, so as to maximize the sum of the weights of the edges having both endpoints in the same subset. We introduce a new class of bounds for this problem relying on the full spectral information of the weighted adjacency matrix A. The expression of these bounds involves the eigenvalues and particular geometrical parameters defined using the eigenvectors of A. A connection is established between these parameters and the maximum cut problem. We report computational results showing that the new bounds compare favorably with previous bounds in the literature. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
21. On (distance) Laplacian energy and (distance) signless Laplacian energy of graphs
- Author
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Pierre Hansen, Mustapha Aouchiche, and Kinkar Chandra Das
- Subjects
Simple graph ,Applied Mathematics ,0211 other engineering and technologies ,Complete graph ,021107 urban & regional planning ,010103 numerical & computational mathematics ,02 engineering and technology ,Mathematics::Spectral Theory ,Signless laplacian ,01 natural sciences ,Graph ,Combinatorics ,Discrete Mathematics and Combinatorics ,Adjacency matrix ,0101 mathematics ,Laplace operator ,Connectivity ,Eigenvalues and eigenvectors ,Mathematics - Abstract
Let G be a graph of order n . The energy E ( G ) of a simple graph G is the sum of absolute values of the eigenvalues of its adjacency matrix. The Laplacian energy, the signless Laplacian energy and the distance energy of graph G are denoted by L E ( G ) , S L E ( G ) and D E ( G ) , respectively. In this paper we introduce a distance Laplacian energy D L E and distance signless Laplacian energy D S L E of a connected graph. We present Nordhaus–Gaddum type bounds on Laplacian energy L E ( G ) and signless Laplacian energy S L E ( G ) in terms of order n of graph G and characterize graphs for which these bounds are best possible. The complete graph and the star give the smallest distance signless Laplacian energy D S L E among all the graphs and trees of order n , respectively. We give lower bounds on distance Laplacian energy D L E in terms of n for graphs and trees, and characterize the extremal graphs. Also we obtain some relations between D E , D S L E and D L E of graph G . Moreover, we give several open problems in this paper.
- Published
- 2018
22. Integral cographs.
- Author
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Allem, Luiz Emilio and Tura, Fernando
- Subjects
- *
EIGENVALUES , *INTEGERS , *MATRICES (Mathematics) - Abstract
A graph is called integral if all the eigenvalues of its adjacency matrix are integers. In this paper, we show that a cograph that has a balanced cotree T G (a 1 , ... , a r − 1 , 0 | 0 , ... , 0 , a r) is integral. We present closed formulas for its eigenvalues. As application, we use the integral cographs to estimate the eigenvalues of any cograph. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
23. On hyper-Hamiltonicity in graphs.
- Author
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Del-Vecchio, Renata R., Vinagre, Cybele T.M., and Pereira, Guilherme B.
- Subjects
- *
HAMILTONIAN graph theory , *LAPLACIAN matrices , *EIGENVALUES - Abstract
A Hamiltonian graph G is said to be hyper-Hamiltonian when G − v is Hamiltonian for any vertex v of G. In this paper, sufficient conditions for a graph to be hyper-Hamiltonian based on different parameters, such as degree and number of edges, are presented. Furthermore, other sufficient conditions for hyper-Hamiltonicity are obtained from spectral parameters, such as the spectral radii of the adjacency matrix, the signless Laplacian matrix and the distance matrix. Results on hyper-Hamiltonicity of a threshold graph through the eigenvalues of its Laplacian matrix are also presented. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
24. Relation between the skew energy of an oriented graph and its matching number
- Author
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Fenglei Tian and Dein Wong
- Subjects
Discrete mathematics ,Applied Mathematics ,0211 other engineering and technologies ,Skew ,021107 urban & regional planning ,010103 numerical & computational mathematics ,02 engineering and technology ,01 natural sciences ,Complete bipartite graph ,Graph ,Combinatorics ,Discrete Mathematics and Combinatorics ,Partition (number theory) ,Adjacency matrix ,0101 mathematics ,Equal size ,Eigenvalues and eigenvectors ,Mathematics - Abstract
Let G σ be an oriented graph with skew adjacency matrix S ( G σ ) . The skew energy E S ( G σ ) of G σ is the sum of the norms of all eigenvalues of S ( G σ ) and the skew rank s r ( G σ ) of G σ is the rank of S ( G σ ) . In this paper, it is proved that E S ( G σ ) ≥ 2 μ ( G ) for an arbitrary connected oriented graph G σ of order n , where μ ( G ) is the matching number of G , and the equality holds if and only if G is a complete bipartite graph K n 2 , n 2 with partition ( X , Y ) of equal size and σ is switching-equivalent to the elementary orientation of G which assigns all edges the same direction from vertices of X to vertices of Y . As an application, we prove that E S ( G σ ) ≥ s r ( G σ ) for an oriented graph G σ and the equality holds if and only if G is the disjoint union of some copies of K 2 and some isolated vertices.
- Published
- 2017
25. Bounds for the energy of weighted graphs.
- Author
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Ganie, Hilal A. and Chat, Bilal A.
- Subjects
- *
WEIGHTED graphs , *GRAPH connectivity , *ABSOLUTE value , *SUM of squares , *GEOMETRIC vertices , *EIGENVALUES - Abstract
Let G be a simple connected graph with n vertices and m edges. Let W (G) = (G , w) be the weighted graph corresponding to G. Let λ 1 , λ 2 , ... , λ n be the eigenvalues of the adjacency matrix A (W (G)) of the weighted graph W (G). The energy E (W (G)) of a weighted graph W (G) is defined as the sum of absolute value of the eigenvalues of W (G). In this paper, we obtain upper bounds for the energy E (W (G)) , in terms of the sum of the squares of weights of the edges, the maximum weight, the maximum degree d 1 , the second maximum degree d 2 and the vertex covering number τ of the underlying graph G. As applications to these upper bounds we obtain some upper bounds for the energy (adjacency energy), the extended graph energy, the Randić energy and the signed energy of the connected graph G. We also obtain some new families of weighted graphs where the energy increases with increase in weights of the edges. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
26. Relating multiway discrepancy and singular values of nonnegative rectangular matrices
- Author
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Marianna Bolla
- Subjects
Discrete mathematics ,Applied Mathematics ,010102 general mathematics ,0102 computer and information sciences ,Directed graph ,Row and column spaces ,01 natural sciences ,Combinatorics ,Singular value ,Matrix (mathematics) ,010201 computation theory & mathematics ,Discrete Mathematics and Combinatorics ,Rank (graph theory) ,Adjacency matrix ,0101 mathematics ,Maxima ,Mathematics - Abstract
The minimum k -way discrepancy md k ( C ) of a rectangular matrix C of nonnegative entries is the minimum of the maxima of the within- and between-cluster discrepancies that can be obtained by simultaneous k -clusterings (proper partitions) of its rows and columns. In Theorem?2, irrespective of the size of C , we give the following estimate for the k th largest nontrivial singular value of the normalized matrix: s k ? 9 md k ( C ) ( k + 2 - 9 k ln md k ( C ) ) , provided 0 < md k ( C ) < 1 and k < rank ( C ) . This statement is a certain converse of Theorem 7 of Bolla (2014), and the proof uses some lemmas and ideas of Butler (2006), where the k = 1 case is treated. The result naturally extends to the singular values of the normalized adjacency matrix of a weighted undirected or directed graph.
- Published
- 2016
27. Non-Singular graphs with a Singular Deck
- Author
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John Baptist Gauci, Irene Sciriha, and Alexander Farrugia
- Subjects
Discrete mathematics ,Applied Mathematics ,Diagonal ,Neighbourhood (graph theory) ,Block matrix ,010103 numerical & computational mathematics ,0102 computer and information sciences ,01 natural sciences ,Graph ,Deck ,Combinatorics ,Computer Science::Discrete Mathematics ,010201 computation theory & mathematics ,Graph power ,Discrete Mathematics and Combinatorics ,Adjacency list ,Adjacency matrix ,0101 mathematics ,Mathematics - Abstract
The n -vertex graph G ( = ? ( G ) ) with a non-singular real symmetric adjacency matrix G , having a zero diagonal and singular ( n - 1 ) × ( n - 1 ) principal submatrices is termed a NSSD, a Non-Singular graph with a Singular Deck. NSSDs arose in the study of the polynomial reconstruction problem and were later found to characterise non-singular molecular graphs that are distinct omni-conductors and ipso omni-insulators. Since both matrices G and G - 1 represent NSSDs ? ( G ) and ? ( G - 1 ) , the value of the nullity of a one-, two- and three-vertex deleted subgraph of G is shown to be determined by the corresponding subgraph in ? ( G - 1 ) . Constructions of infinite subfamilies of non-NSSDs are presented. NSSDs with all two-vertex deleted subgraphs having a common value of the nullity are referred to as G -nutful graphs. We show that their minimum vertex degree is at least 4.
- Published
- 2016
28. Hyperspherical embedding of graphs and networks in communicability spaces
- Author
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M. G. Sánchez-Lirola, José Antonio de la Peña, and Ernesto Estrada
- Subjects
Discrete mathematics ,Generic property ,Applied Mathematics ,Positive-definite matrix ,Hypersphere ,Euclidean distance ,Combinatorics ,symbols.namesake ,Taylor series ,symbols ,Discrete Mathematics and Combinatorics ,Embedding ,Adjacency matrix ,Connectivity ,Mathematics - Abstract
Let G be a simple connected graph with n nodes and let f"@a"""k(A) be a communicability function of the adjacency matrix A, which is expressible by the following Taylor series expansion: @?"k"="0^[email protected]"kA^k. We prove here that if f"@a"""k(A) is positive semidefinite then the function @h"p","q=(f"@a"""k(A)"p"p+f"@a"""k(A)"q"q-2f"@a"""k(A)"p"q)^1^2 is a Euclidean distance between the corresponding nodes of the graph. Then, we prove that if f"@a"""k(A) is positive definite, the communicability distance induces an embedding of the graph into a hyperdimensional sphere (hypersphere) such as the distances between the nodes are given by @h"p","q. In addition we give analytic results for the communicability distances for the nodes in paths, cycles, stars and complete graphs, and we find functions of the adjacency matrix for which the main results obtained here are applicable. Finally, we study the ratio of the surface area to volume of the hyperspheres in which a few real-world networks are embedded. We give clear indications about the usefulness of this embedding in analyzing the efficacy of geometrical embeddings of real-world networks like brain networks, airport transportation networks and the Internet.
- Published
- 2014
29. Adjacency matrices of probe interval graphs
- Author
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Maitry Podder, Shamik Ghosh, and Malay K. Sen
- Subjects
Interval bigraph ,Discrete mathematics ,Degree matrix ,Ferrers bigraph ,Applied Mathematics ,Interval graph ,law.invention ,Probe interval graph ,Combinatorics ,Graph energy ,law ,Seidel adjacency matrix ,Adjacency matrix of a graph ,Line graph ,Discrete Mathematics and Combinatorics ,Adjacency list ,Regular graph ,Adjacency matrix ,Ferrers dimension ,Mathematics - Abstract
In this paper we obtain several characterizations of the adjacency matrix of a probe interval graph. In course of this study we describe an easy method of obtaining interval representation of an interval bigraph from its adjacency matrix. Finally, we note that if we add a loop at every probe vertex of a probe interval graph, then the Ferrers dimension of the corresponding symmetric bipartite graph is at most 3.
- Published
- 2010
30. The Pfaffian property of circulant graphs
- Author
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Yan Wang, Lianzhu Zhang, and Fuliang Lu
- Subjects
Combinatorics ,Discrete mathematics ,Circulant graph ,Graph power ,Applied Mathematics ,Discrete Mathematics and Combinatorics ,Pfaffian ,Bound graph ,Adjacency matrix ,Time complexity ,Circulant matrix ,Graph ,Mathematics - Abstract
The importance of the Pfaffian property of a graph stems from the fact that if the graph is Pfaffian, then the number of its perfect matchings can be computed in polynomial time. A graph G is Pfaffian if there exists an orientation of G , denoted by G ? , such that the determinant of the skew adjacency matrix of G ? equals the square of the number of perfect matchings of G . An undirected graph G = ( V , E ) with n vertices is a circulant graph, denoted by C n ( a 1 , a 2 , ? , a m ) , if there exists a labeling of the vertices of G , v 1 , v 2 , ? , v n , and m integers, a 1 , a 2 , ? , a m , such that the edge set E = { v i v j : i - j ? ? a k ( mod n ) for? 1 ? k ? m } . In this paper, the Pfaffian property of circulant graphs is completely characterized, that is, a simple connected circulant graph C n ( a 1 , a 2 , ? , a m ) of even order is Pfaffian if and only if m = 1 or, m = 2 and a 1 + a 2 is odd.
- Published
- 2015
31. On linear algebra of balance-binomial graphs.
- Author
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Kar, Kübra and Yılmaz, Fatih
- Subjects
- *
LINEAR algebra , *BINOMIAL equations , *COEFFICIENTS (Statistics) , *GRAPHIC methods , *MATRICES (Mathematics) - Abstract
In this work, we introduce balance-binomial graphs, whose entries of adjacency matrix are balance-binomial coefficients. Then we obtain some characteristic properties of the graph. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
32. State transfer and star complements in graphs
- Author
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Changjiang Bu and Jiang Zhou
- Subjects
Discrete mathematics ,Combinatorics ,Applied Mathematics ,Neighbourhood (graph theory) ,Induced subgraph ,Discrete Mathematics and Combinatorics ,Multiplicity (mathematics) ,Unitary operator ,Adjacency matrix ,Quantum information ,Eigenvalues and eigenvectors ,Vertex (geometry) ,Mathematics - Abstract
Let G be a graph with adjacency matrix A, and let H(t)=exp(itA). For an eigenvalue @m of A with multiplicity k, a star set for @m in G is a vertex set X of G such that |X|=k and the induced subgraph G-X does not have @m as an eigenvalue. G is said to have perfect state transfer from the vertex u to the vertex v if there is a time @t such that |H(@t)"u","v|=1. The unitary operator H(t) has important applications in the transfer of quantum information. In this paper, we give an expression of H(t). For a star set X of graph G, perfect state transfer does not occur between any two vertices in X. We also give some results for the existence of perfect state transfer in a graph.
- Published
- 2014
33. On the connectivity properties and energy of Fibonomial graphs
- Author
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Ahmet Öteleş, Akın Kale, and Mehmet Akbulak
- Subjects
Combinatorics ,Discrete mathematics ,Algebraic connectivity ,Computer Science::Discrete Mathematics ,Applied Mathematics ,Modulo ,Discrete Mathematics and Combinatorics ,Adjacency matrix ,Mathematics::Spectral Theory ,Laplacian eigenvalues ,Graph ,Eigenvalues and eigenvectors ,Mathematics - Abstract
We introduce a new type of graph called a Fibonomial graph, denoted G"n. Entries of the adjacency matrix of G"n depend on the well-known Fibonomial coefficients modulo 2. We investigate the connectivity properties, eigenvalues, and energy of G"n. We lastly obtain the sum of the Laplacian eigenvalues of G"n.
- Published
- 2014
34. Bounds for the matching number, the edge chromatic number and the independence number of a graph in terms of rank
- Author
-
Long Wang and Dein Wong
- Subjects
Vertex (graph theory) ,Connected component ,Combinatorics ,Discrete mathematics ,Edge coloring ,Simple graph ,Applied Mathematics ,Discrete Mathematics and Combinatorics ,Adjacency matrix ,Chromatic scale ,Graph ,Mathematics ,Independence number - Abstract
Let G = ( V , E ) be a simple graph with vertex set V and edge set E . The rank of G , written as r , is defined to be the rank of its adjacency matrix. Let c denote e - v + ? , where e = | E | , v = | V | and ? means the number of connected components of G , and let m , α , ? ' respectively be the matching number, the independence number, and the chromatic index of G . In this paper, it is proved that ? r - c 2 ? ? m ? ? r + 2 c 2 ? , ? 2 e r + 2 c ? ? ? ' , and v - ? r 2 ? - c ? α ? v - ? r 2 ? . Examples are given to show that all the bounds can be attained.
- Published
- 2014
35. Tricyclic graph with maximal Estrada index
- Author
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Zhongyi Qiu, Liansheng Tan, and Zhongxun Zhu
- Subjects
Combinatorics ,Discrete mathematics ,Estrada index ,Applied Mathematics ,Discrete Mathematics and Combinatorics ,Adjacency matrix ,Connectivity ,Eigenvalues and eigenvectors ,Graph ,Mathematics - Abstract
Let G be a simple connected graph on n vertices and λ 1 , λ 2 , ? , λ n be the eigenvalues of the adjacency matrix of G . The Estrada index of G is defined as E E ( G ) = ? i = 1 n e λ i . Let T n be the class of tricyclic graphs G on n vertices. In this paper, the graphs in T n with the maximal Estrada index is characterized.
- Published
- 2014
36. An algebraic approach to lifts of digraphs
- Author
-
Jozef Širáň, Miguel Angel Fiol, Cristina Dalfó, Mirka Miller, Joe Ryan, Universitat Politècnica de Catalunya. Departament de Matemàtiques, and Universitat Politècnica de Catalunya. COMBGRAPH - Combinatòria, Teoria de Grafs i Aplicacions
- Subjects
Regular partition ,Quotient digraph ,05C20, 05C50, 15A18 ,0211 other engineering and technologies ,0102 computer and information sciences ,02 engineering and technology ,01 natural sciences ,spectrum ,Combinatorics ,Lift (mathematics) ,Computer Science::Discrete Mathematics ,FOS: Mathematics ,Discrete Mathematics and Combinatorics ,Mathematics - Combinatorics ,Adjacency matrix ,Algebraic number ,Abelian group ,Mathematics ,Mathematics::Combinatorics ,Grafs, Teoria de ,Applied Mathematics ,Digraph ,021107 urban & regional planning ,Generalized Petersen graph ,Graph ,Graph theory ,010201 computation theory & mathematics ,Voltage digraphs ,Combinatorics (math.CO) ,Lifted digraph ,Directed graphs ,Matemàtiques i estadística::Matemàtica discreta::Teoria de grafs [Àrees temàtiques de la UPC] - Abstract
We present some applications of a new matrix approach for studying the properties of the lift of a voltage digraph, which has arcs weighted by the elements of a group. As a main result, when the involved group is Abelian, we completely determine the spectrum of . As some examples of our technique, we study some basic properties of the Alegre digraph, and completely characterize the spectrum of a new family of digraphs, which contains the generalized Petersen graphs, and the Hoffman-Singleton graph The research of the first two authors have been partially supported by the Agency for Management of University and Research Grants of Catalonia (AGAUR) under project 2017SGR1087. The fifth author acknowledges support from the research grants APVV 0136/12, APVV-15-0220, VEGA 1/0026/16, and VEGA 1/0142/17. The first author has also received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sk lodowska-Curie grant agreement No 734922.
- Published
- 2018
- Full Text
- View/download PDF
37. An edge grafting theorem on the Estrada index of graphs and its applications
- Author
-
Zhibin Du
- Subjects
Discrete mathematics ,Spectral moments ,Closed walks ,Applied Mathematics ,Pendent paths ,Edge grafting operation ,Graph ,Combinatorics ,Estrada index ,Discrete Mathematics and Combinatorics ,Adjacency matrix ,Eigenvalues and eigenvectors ,Mathematics - Abstract
The Estrada index of a graph G is defined as EE(G)[email protected]?"i"="1^ne^@l^"^i, where @l"1,@l"2,...,@l"n are the eigenvalues of the adjacency matrix of G. It can be used as an efficient measuring tool in a variety of fields. An edge grafting operation on a graph moves a pendent edge between two pendent paths. In this paper, we give an edge grafting theorem on the Estrada index of graphs. We also give some applications of this theorem.
- Published
- 2013
- Full Text
- View/download PDF
38. Distance spectral radius of trees with given matching number
- Author
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Aleksandar Ilic
- Subjects
Distance matrix ,Hosoya index ,Graph center ,Matching (graph theory) ,Spectral radius ,Applied Mathematics ,Wiener index ,Trees ,Combinatorics ,Graph energy ,Matching ,Discrete Mathematics and Combinatorics ,Adjacency matrix ,Distance spectral radius ,Mathematics - Abstract
The distance spectral radius @r(G) of a graph G is the largest eigenvalue of the distance matrix D(G). Recently, many researches proposed the use of @r(G) as a molecular structure descriptor of alkanes. In this paper, we introduce general transformations that decrease distance spectral radius and characterize n-vertex trees with given matching number m which minimize the distance spectral radius. The extremal tree A(n,m) is a spur, obtained from the star graph S"n"-"m"+"1 with n-m+1 vertices by attaching a pendent edge to each of certain m-1 non-central vertices of S"n"-"m"+"1. The resulting trees also minimize the spectral radius of adjacency matrix, Hosoya index, Wiener index and graph energy in the same class of trees. In conclusion, we pose a conjecture for the maximal case based on the computer search among trees on n@?24 vertices. In addition, we found the extremal tree that uniquely maximizes the distance spectral radius among n-vertex trees with perfect matching and fixed maximum degree @D.
- Published
- 2010
39. Matrix power inequalities and the number of walks in graphs
- Author
-
Jeremias Weihmann and Hanjo Täubig
- Subjects
Combinatorics ,Discrete mathematics ,Unification ,Spectral radius ,Applied Mathematics ,Discrete Mathematics and Combinatorics ,Symmetric matrix ,Adjacency matrix ,Nonnegative matrix ,Hermitian matrix ,Squeeze theorem ,Vertex (geometry) ,Mathematics - Abstract
We unify and generalize several inequalities for the number w"k of walks of length k in graphs, and for the entry sum of matrix powers. First, we present a weighted sandwich theorem for Hermitian matrices which generalizes a matrix theorem by Marcus and Newman and which further generalizes our former unification of inequalities for the number of walks in undirected graphs by Lagarias et al. and by Dress and Gutman. The new inequality uses an arbitrary nonnegative weighting of the indices (vertices) which allows to apply the theorem to index (vertex) subsets (i.e., inequalities considering the number w"k(S,S) of walks of length k that start at a vertex of a given vertex subset S and that end within the same subset). We also deduce a stronger variation of the sandwich theorem for the case of positive-semidefinite Hermitian matrices which generalizes another inequality of Marcus and Newman. Further, we show a similar theorem for nonnegative symmetric matrices which is another unification and generalization of inequalities for walk numbers by Erdos and Simonovits, by Dress and Gutman, and by Ilic and Stevanovic. In the last part, we generalize lower bounds for the spectral radius of adjacency matrices and upper bounds for the energy of graphs.
- Published
- 2014
40. On the minimal energy ordering of trees with perfect matchings
- Author
-
Ji-Ming Guo
- Subjects
Discrete mathematics ,Energy ,Applied Mathematics ,Eigenvalues ,Graph ,Characteristic polynomial ,Combinatorics ,Discrete Mathematics and Combinatorics ,Perfect matching ,Adjacency matrix ,Tree ,Eigenvalues and eigenvectors ,Mathematics - Abstract
The energy of a graph is defined as the sum of the absolute values of all eigenvalues of the adjacency matrix of the graph. Zhang and Li [F. Zhang, H. Li, On acyclic conjugated molecules with minimal energies, Discrete Appl. Math. 92 (1999) 71–84] determined the first two smallest-energy trees of a fixed size with a perfect matching and showed that the third minimal energy is between two trees. This paper characterizes trees of a fixed size with a perfect matching with third minimal, fourth minimal and fifth minimal energies for n≥86 and third minimal, fourth minimal energies for 14≤n≤84.
- Published
- 2008
41. Ordering graphs with index in the interval (2,2+5)
- Author
-
Slobodan K. Simić, Francesco Belardo, and Enzo M. Li Marzi
- Subjects
Combinatorics ,Indifference graph ,Pathwidth ,Chordal graph ,Applied Mathematics ,Trapezoid graph ,Discrete Mathematics and Combinatorics ,Interval graph ,Maximal independent set ,Adjacency matrix ,1-planar graph ,Mathematics - Abstract
The index of a graph is the largest eigenvalue (or spectral radius) of its adjacency matrix. We consider the problem of ordering graphs by the index in the class of connected graphs with a fixed order n and index belonging to the interval (2,2+5). For any fixed n (provided that n is not too small), we order a significant portion of graphs whose indices are close to the end points of the above interval.
- Published
- 2008
42. Hamiltonicity of regular graphs and blocks of consecutive ones in symmetric matrices
- Author
-
Yingchao Zhao, Francis C. M. Lau, and Rui Wang
- Subjects
Discrete mathematics ,Hamiltonicity ,Applied Mathematics ,Block matrix ,Incidence matrix ,Hamiltonian path ,NP-completeness ,Combinatorics ,symbols.namesake ,Regular graph ,symbols ,Consecutive ones ,Discrete Mathematics and Combinatorics ,Symmetric matrix ,Logical matrix ,Adjacency matrix ,Row ,Mathematics - Abstract
We show that the Hamiltonicity of a regular graph G can be fully characterized by the numbers of blocks of consecutive ones in the binary matrix A+I, where A is the adjacency matrix of G, I is the unit matrix, and the blocks can be either linear or circular. Concretely, a k-regular graph G with girth g(G)⩾5 has a Hamiltonian circuit if and only if the matrix A+I can be permuted on rows such that each column has at most (or exactly) k-1 circular blocks of consecutive ones; and if the graph G is k-regular except for two (k-1)-degree vertices a and b, then there is a Hamiltonian path from a to b if and only if the matrix A+I can be permuted on rows to have at most (or exactly) k-1 linear blocks per column.Then we turn to the problem of determining whether a given matrix can have at most k blocks of consecutive ones per column by some row permutation. For this problem, Booth and Lueker gave a linear algorithm for k=1 [Proceedings of the Seventh Annual ACM Symposium on Theory of Computing, 1975, pp. 255–265]; Flammini et al. showed its NP-completeness for general k [Algorithmica 16 (1996) 549–568]; and Goldberg et al. proved the same for every fixed k⩾2 [J. Comput. Biol. 2 (1) (1995) 139–152]. In this paper, we strengthen their result by proving that the problem remains NP-complete for every constant k⩾2 even if the matrix is restricted to (1) symmetric, or (2) having at most three blocks per row.
- Published
- 2007
43. Generating effective symmetry-breaking predicates for search problems
- Author
-
Ilya Shlyakhter
- Subjects
Discrete mathematics ,Backtracking ,Applied Mathematics ,Binary number ,Directed graph ,Measure (mathematics) ,Satisfiability ,Combinatorics ,Permutation ,Matrix (mathematics) ,Discrete Mathematics and Combinatorics ,Logical matrix ,Adjacency matrix ,Isomorphism class ,Isomorphism ,Boolean satisfiability problem ,Mathematics ,MathematicsofComputing_DISCRETEMATHEMATICS - Abstract
Consider the problem of testing for existence of an n-node graph G satisfying some condition P, expressed as a Boolean constraint among the nxn Boolean entries of the adjacency matrix M. This problem reduces to satisfiability of P(M). If P is preserved by isomorphism, P(M) is satisfiable iff P(M)@?SB(M) is satisfiable, where SB(M) is a symmetry-breaking predicate-a predicate satisfied by at least one matrix M in each isomorphism class. P(M)@?SB(M) is more constrained than P(M), so it is solved faster by backtracking than P(M)-especially if SB(M) rules out most matrices in each isomorphism class. This method, proposed by Crawford et al., applies not just to graphs but to testing existence of a combinatorial object satisfying any property that respects isomorphism, as long as the property can be compactly specified as a Boolean constraint on the object's binary representation. We present methods for generating symmetry-breaking predicates for several classes of combinatorial objects: acyclic digraphs, permutations, functions, and arbitrary-arity relations (direct products). We define a uniform optimality measure for symmetry-breaking predicates, and evaluate our constraints according to this measure. Results indicate that these constraints are either optimal or near-optimal for their respective classes of objects.
- Published
- 2007
- Full Text
- View/download PDF
44. On split graphs with four distinct eigenvalues.
- Author
-
Goldberg, Felix, Kirkland, Steve, Varghese, Anu, and Vijayakumar, Ambat
- Subjects
- *
DIAMETER - Abstract
It is a well-known fact that a graph of diameter d has at least d + 1 eigenvalues. A graph is d -extremal, if it has diameter d and exactly d + 1 eigenvalues. A graph is split if its vertex set can be partitioned into a clique and a stable set. Such graphs have diameter at most 3. We obtain a complete classification of the connected bidegreed 3-extremal split graphs using the association of split graphs with combinatorial designs. We also construct certain families of non-bidegreed 3-extremal split graphs. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
45. Non-Singular graphs with a Singular Deck.
- Author
-
Farrugia, Alexander, Gauci, John Baptist, and Sciriha, Irene
- Subjects
- *
GRAPH theory , *MATHEMATICAL symmetry , *MATRICES (Mathematics) , *MOLECULAR graphs , *ELECTRICAL conductors , *SUBGRAPHS - Abstract
The n -vertex graph G ( = Γ ( G ) ) with a non-singular real symmetric adjacency matrix G , having a zero diagonal and singular ( n − 1 ) × ( n − 1 ) principal submatrices is termed a NSSD, a Non-Singular graph with a Singular Deck. NSSDs arose in the study of the polynomial reconstruction problem and were later found to characterise non-singular molecular graphs that are distinct omni-conductors and ipso omni-insulators. Since both matrices G and G − 1 represent NSSDs Γ ( G ) and Γ ( G − 1 ) , the value of the nullity of a one-, two- and three-vertex deleted subgraph of G is shown to be determined by the corresponding subgraph in Γ ( G − 1 ) . Constructions of infinite subfamilies of non-NSSDs are presented. NSSDs with all two-vertex deleted subgraphs having a common value of the nullity are referred to as G -nutful graphs. We show that their minimum vertex degree is at least 4. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
46. On strongly regular signed graphs.
- Author
-
Stanić, Zoran
- Subjects
- *
REGULAR graphs - Abstract
In this paper we consider a concept of strong regularity of signed graphs—a generalization of strong regularity of graphs. We establish certain structural and spectral properties of such signed graphs and determine or characterize those belonging to specified classes. Theoretical results are followed by examples and discussions. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
47. Graph models and their efficient implementation for sparse Jacobian matrix determination
- Author
-
Trond Steihaug and Shahadat Hossain
- Subjects
Theoretical computer science ,Applied Mathematics ,Incidence matrix ,Directed graph ,Butterfly graph ,law.invention ,law ,Line graph ,Discrete Mathematics and Combinatorics ,Graph (abstract data type) ,Adjacency matrix ,Null graph ,Graph property ,Mathematics - Abstract
Large-scale combinatorial scientific computing problems arising in sparse or otherwise structured matrix computation are often expressed using an appropriate graph model, and sometimes the same problem can be given in more than one graph model with similar asymptotic computational complexity. The relative merits of different graph models for the same problem can then be expressed in terms of factors such as generality of the model or ease of computer implementation. We review contemporary graph formulations for large-scale sparse Jacobian matrix determination problem (JMDP) and suggest the pattern graph as a unifying framework for methods that exploit sparsity by matrix compression: row compression, column compression, or a combination of the two. We argue that with the pattern graph, which is structurally close to the underlying matrix, exploitable sparsity and structures in the matrix are unlikely to be lost in ''translation'' from a matrix problem to a graph problem. From an algorithmic view point the structural correspondence between the matrix and its graph, as we demonstrate in this paper, leads to a better exposition of the compression heuristics and their efficient computer realization. Array-based data structures are suggested as the basic building-blocks for the efficient implementation of relevant graph algorithms. Results from the numerical testing of a subset of implemented algorithms on a suite of test instances drawn from the standard test matrix collection are presented.
- Published
- 2013
48. The underlying line digraph structure of some (0,1)-matrix equations
- Author
-
Yaokun Wu and Joan Gimbert
- Subjects
Discrete mathematics ,Polynomial ,Mathematics::Combinatorics ,(0,1)-matrix equation ,Applied Mathematics ,Moore bound ,Digraph ,Line digraph ,Combinatorics ,Matrix (mathematics) ,Integer ,Computer Science::Discrete Mathematics ,Iterated function ,Cycle graph ,Order (group theory) ,Discrete Mathematics and Combinatorics ,Adjacency matrix ,Mathematics - Abstract
From the theory ofHo0man polynomial, it is known that the adjacency matrix A ofa strongly connected regular digraph oforder n satis3es certain polynomial equation A l P(A)=Jn, where l is a nonnegative integer, P(x) is a polynomial with rational coe5cients, and Jn is the n×n matrix of all ones. In this paper we present some su5cient conditions, in terms ofthe coe5cients of P(x), to ensure that all (0; 1)-matrices satisfying such an equation with l? 0 have an underlying line digraph structure, that is to say, for any solution A there exists a (0; 1)-matrix C satisfying P(C)= Jn=dl and the associated (d-regular) digraph of A, � (A), is the lth iterated line digraph of � (C). As a result, we simplify the study of some digraph classes with order functions asymptotically attaining the Moore bound. ? 2002 Elsevier Science B.V. All rights reserved.
- Published
- 2002
- Full Text
- View/download PDF
49. Adjacency matrices of probe interval graphs
- Author
-
Ghosh, Shamik, Podder, Maitry, and Sen, Malay K.
- Subjects
- *
BIPARTITE graphs , *INTERVAL analysis , *MATHEMATICAL proofs , *DIMENSIONAL analysis , *MATHEMATICAL symmetry , *MATHEMATICAL analysis - Abstract
Abstract: In this paper we obtain several characterizations of the adjacency matrix of a probe interval graph. In course of this study we describe an easy method of obtaining interval representation of an interval bigraph from its adjacency matrix. Finally, we note that if we add a loop at every probe vertex of a probe interval graph, then the Ferrers dimension of the corresponding symmetric bipartite graph is at most 3. [ABSTRACT FROM AUTHOR]
- Published
- 2010
- Full Text
- View/download PDF
50. Graph spectra as a systematic tool in computational biology
- Author
-
Anirban Banerjee and Jürgen Jost
- Subjects
Theoretical computer science ,Biological network ,Neuronal network ,FOS: Physical sciences ,Quantitative Biology - Quantitative Methods ,Spectral plot ,Protein–protein interaction network ,Foodweb ,Discrete Mathematics and Combinatorics ,Integral graph ,Adjacency matrix ,Quantitative Methods (q-bio.QM) ,Graph spectrum ,Mathematics ,Spectral graph theory ,Applied Mathematics ,Transcription network ,Voltage graph ,Metabolic network ,Mathematics::Spectral Theory ,Nonlinear Sciences - Adaptation and Self-Organizing Systems ,Graph energy ,Graph evolution ,FOS: Biological sciences ,Graph (abstract data type) ,Laplacian matrix ,Null graph ,Adaptation and Self-Organizing Systems (nlin.AO) ,Algorithm - Abstract
We present the spectrum of the (normalized) graph Laplacian as a systematic tool for the investigation of networks, and we describe basic properties of eigenvalues and eigenfunctions. Processes of graph formation like motif joining or duplication leave characteristic traces in the spectrum. This can suggest hypotheses about the evolution of a graph representing biological data. To this data, we analyze several biological networks in terms of rough qualitative data of their spectra., Comment: 12 pages, 3 figures, Discrete Applied Mathematics, to appear
- Published
- 2009
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