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Wyświetlanie 1-15 z 29
Tytuł:
Notes on the independence number in the Cartesian product of graphs
Autorzy:
Abay-Asmerom, G.
Hammack, R.
Larson, C.
Taylor, D.
Powiązania:
https://bibliotekanauki.pl/articles/744113.pdf
Data publikacji:
2011
Wydawca:
Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
Tematy:
independence number
Cartesian product
critical independent set
radius
r-ciliate
Opis:
Every connected graph G with radius r(G) and independence number α(G) obeys α(G) ≥ r(G). Recently the graphs for which equality holds have been classified. Here we investigate the members of this class that are Cartesian products. We show that for non-trivial graphs G and H, α(G ☐ H) = r(G ☐ H) if and only if one factor is a complete graph on two vertices, and the other is a nontrivial complete graph. We also prove a new (polynomial computable) lower bound α(G ☐ H) ≥ 2r(G)r(H) for the independence number and we classify graphs for which equality holds.
The second part of the paper concerns independence irreducibility. It is known that every graph G decomposes into a König-Egervary subgraph (where the independence number and the matching number sum to the number of vertices) and an independence irreducible subgraph (where every non-empty independent set I has more than |I| neighbors). We examine how this decomposition relates to the Cartesian product. In particular, we show that if one of G or H is independence irreducible, then G ☐ H is independence irreducible.
Źródło:
Discussiones Mathematicae Graph Theory; 2011, 31, 1; 25-35
2083-5892
Pojawia się w:
Discussiones Mathematicae Graph Theory
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Coloring Some Finite Sets in $ \mathbb{R}^n $
Autorzy:
Balogh, József
Kostochka, Alexandr
Raigorodskii, Andrei
Powiązania:
https://bibliotekanauki.pl/articles/30146863.pdf
Data publikacji:
2013-03-01
Wydawca:
Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
Tematy:
chromatic number
independence number
distance graph
Opis:
This note relates to bounds on the chromatic number $ \chi (\mathbb{R}^n)$ of the Euclidean space, which is the minimum number of colors needed to color all the points in $ \mathbb{R}^n$ so that any two points at the distance 1 receive different colors. In [6] a sequence of graphs $ G_n $ in $ \mathbb{R}_n $ was introduced showing that $ \chi(\mathbb{R}^n) \ge \chi(G_n) \ge (1+ o(1))\frac{n^2}{6} $. For many years, this bound has been remaining the best known bound for the chromatic numbers of some lowdimensional spaces. Here we prove that $ \chi(G_n) \sim \frac{n^2}{6} $ and find an exact formula for the chromatic number in the case of $ n = 2^k $ and $ n = 2^k − 1 $.
Źródło:
Discussiones Mathematicae Graph Theory; 2013, 33, 1; 25-31
2083-5892
Pojawia się w:
Discussiones Mathematicae Graph Theory
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Complete minors, independent sets, and chordal graphs
Autorzy:
Balogh, József
Lenz, John
Wu, Hehui
Powiązania:
https://bibliotekanauki.pl/articles/743579.pdf
Data publikacji:
2011
Wydawca:
Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
Tematy:
clique minor
independence number
Hadwiger conjecture
chordal graphs
Opis:
The Hadwiger number h(G) of a graph G is the maximum size of a complete minor of G. Hadwiger's Conjecture states that h(G) ≥ χ(G). Since χ(G) α(G) ≥ |V(G)|, Hadwiger's Conjecture implies that α(G) h(G) ≥ |V(G)|. We show that (2α(G) - ⌈log_{τ}(τα(G)/2)⌉) h(G) ≥ |V(G)| where τ ≍ 6.83. For graphs with α(G) ≥ 14, this improves on a recent result of Kawarabayashi and Song who showed (2α(G) - 2) h(G) ≥ |V(G) | when α(G) ≥ 3.
Źródło:
Discussiones Mathematicae Graph Theory; 2011, 31, 4; 639-674
2083-5892
Pojawia się w:
Discussiones Mathematicae Graph Theory
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Independence Number and Packing Coloring of Generalized Mycielski Graphs
Autorzy:
Bidine, Ez Zobair
Gadi, Taoufiq
Kchikech, Mustapha
Powiązania:
https://bibliotekanauki.pl/articles/32222704.pdf
Data publikacji:
2021-08-01
Wydawca:
Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
Tematy:
independence number
packing chromatic number
Mycielskians
generalized Mycielskians
Opis:
For a positive integer k ⩾ 1, a graph G with vertex set V is said to be k-packing colorable if there exists a mapping f : V ↦ {1, 2, . . ., k} such that any two distinct vertices x and y with the same color f(x) = f(y) are at distance at least f(x) + 1. The packing chromatic number of a graph G, denoted by χρ(G), is the smallest integer k such that G is k-packing colorable. In this work, we study both independence and packing colorings in the m-generalized Mycielskian of a graph G, denoted μm(G). We first give an explicit formula for α (μm(G)) when m is odd and bounds when m is even. We then use these results to give exact values of α(μm(Kn)) for any m and n. Next, we give bounds on the packing chromatic number, χρ, of μm(G). We also prove the existence of large planar graphs whose packing chromatic number is 4. The rest of the paper is focused on packing chromatic numbers of the Mycielskian of paths and cycles.
Źródło:
Discussiones Mathematicae Graph Theory; 2021, 41, 3; 725-747
2083-5892
Pojawia się w:
Discussiones Mathematicae Graph Theory
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
The Quest for A Characterization of Hom-Properties of Finite Character
Autorzy:
Broere, Izak
Matsoha, Moroli D.V.
Heidema, Johannes
Powiązania:
https://bibliotekanauki.pl/articles/31340894.pdf
Data publikacji:
2016-05-01
Wydawca:
Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
Tematy:
(countable) graph
homomorphism (of graphs)
property of graphs
hom-property
(finitely-)induced-hereditary property
finitely determined property
(weakly) finite character
axiomatizable property
compactness theorems
core
connectedness
chromatic number
clique number
independence number
dominating set
Opis:
A graph property is a set of (countable) graphs. A homomorphism from a graph \( G \) to a graph \( H \) is an edge-preserving map from the vertex set of \( G \) into the vertex set of \( H \); if such a map exists, we write \( G \rightarrow H \). Given any graph \( H \), the hom-property \( \rightarrow H \) is the set of \( H \)-colourable graphs, i.e., the set of all graphs \( G \) satisfying \( G \rightarrow H \). A graph property \( mathcal{P} \) is of finite character if, whenever we have that \( F \in \mathcal{P} \) for every finite induced subgraph \( F \) of a graph \( G \), then we have that \( G \in \mathcal{P} \) too. We explore some of the relationships of the property attribute of being of finite character to other property attributes such as being finitely-induced-hereditary, being finitely determined, and being axiomatizable. We study the hom-properties of finite character, and prove some necessary and some sufficient conditions on \( H \) for \( \rightarrow H \) to be of finite character. A notable (but known) sufficient condition is that \( H \) is a finite graph, and our new model-theoretic proof of this compactness result extends from hom-properties to all axiomatizable properties. In our quest to find an intrinsic characterization of those \( H \) for which \( \rightarrow H \) is of finite character, we find an example of an infinite connected graph with no finite core and chromatic number 3 but with hom-property not of finite character.
Źródło:
Discussiones Mathematicae Graph Theory; 2016, 36, 2; 479-500
2083-5892
Pojawia się w:
Discussiones Mathematicae Graph Theory
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
New Results Relating Independence and Matchings
Autorzy:
Caro, Yair
Davila, Randy
Pepper, Ryan
Powiązania:
https://bibliotekanauki.pl/articles/32304143.pdf
Data publikacji:
2022-08-01
Wydawca:
Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
Tematy:
independent sets
independence number
matchings
matching number
Opis:
In this paper we study relationships between the matching number, written µ(G), and the independence number, written α(G). Our first main result is to show α(G) ≤ µ(G) + |X| − µ(G[NG[X]]), where X is any intersection of maximum independent sets in G. Our second main result is to show δ(G) α(G) ≤ Δ(G)µ(G), where δ(G) and Δ(G) denote the minimum and maximum vertex degrees of G, respectively. These results improve on and generalize known relations between µ(G) and α(G). Further, we also give examples showing these improvements.
Źródło:
Discussiones Mathematicae Graph Theory; 2022, 42, 3; 921-935
2083-5892
Pojawia się w:
Discussiones Mathematicae Graph Theory
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Bounds on the 2-domination number in cactus graphs
Autorzy:
Chellali, M.
Powiązania:
https://bibliotekanauki.pl/articles/254915.pdf
Data publikacji:
2006
Wydawca:
Akademia Górniczo-Hutnicza im. Stanisława Staszica w Krakowie. Wydawnictwo AGH
Tematy:
2-domination number
total domination number
independence number
cactus graphs
trees
Opis:
A 2-dominating set of a graph G is a set D of vertices of G such that every vertex not in S is dominated at least twice. The minimum cardinality of a 2-dominating set of G is the 2-domination number γ2(G). We show that if G is a nontrivial connected cactus graph with k(G) even cycles (k(G) ≥ 0), then γ2(G) ≥ γt(G) - k(G), and if G is a graph of order n with at most one cycle, then γ2(G) ≥ (n + l - s)/2 improving Fink and Jacobson's lower bound for trees with l > s, where γt(G), l and s are the total domination number, the number of leaves and support vertices of G, respectively. We also show that if T is a tree of order n ≥ 3, then γ2(T) ≤ β(T) + s - 1, where β(T) is the independence number of T.
Źródło:
Opuscula Mathematica; 2006, 26, 1; 5-12
1232-9274
2300-6919
Pojawia się w:
Opuscula Mathematica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Bounds on the global offensive k-alliance number in graphs
Autorzy:
Chellali, Mustapha
Haynes, Teresa
Randerath, Bert
Volkmann, Lutz
Powiązania:
https://bibliotekanauki.pl/articles/744476.pdf
Data publikacji:
2009
Wydawca:
Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
Tematy:
global offensive k-alliance number
independence number
chromatic number
Opis:
Let G = (V(G),E(G)) be a graph, and let k ≥ 1 be an integer. A set S ⊆ V(G) is called a global offensive k-alliance if |N(v)∩S| ≥ |N(v)-S|+k for every v ∈ V(G)-S, where N(v) is the neighborhood of v. The global offensive k-alliance number $γₒ^k(G)$ is the minimum cardinality of a global offensive k-alliance in G. We present different bounds on $γₒ^k(G)$ in terms of order, maximum degree, independence number, chromatic number and minimum degree.
Źródło:
Discussiones Mathematicae Graph Theory; 2009, 29, 3; 597-613
2083-5892
Pojawia się w:
Discussiones Mathematicae Graph Theory
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Global alliances and independence in trees
Autorzy:
Chellali, Mustapha
Haynes, Teresa
Powiązania:
https://bibliotekanauki.pl/articles/743643.pdf
Data publikacji:
2007
Wydawca:
Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
Tematy:
defensive alliance
offensive alliance
global alliance
domination
trees
independence number
Opis:
A global defensive (respectively, offensive) alliance in a graph G = (V,E) is a set of vertices S ⊆ V with the properties that every vertex in V-S has at least one neighbor in S, and for each vertex v in S (respectively, in V-S) at least half the vertices from the closed neighborhood of v are in S. These alliances are called strong if a strict majority of vertices from the closed neighborhood of v must be in S. For each kind of alliance, the associated parameter is the minimum cardinality of such an alliance. We determine relationships among these four parameters and the vertex independence number for trees.
Źródło:
Discussiones Mathematicae Graph Theory; 2007, 27, 1; 19-27
2083-5892
Pojawia się w:
Discussiones Mathematicae Graph Theory
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Trees with equal 2-domination and 2-independence numbers
Autorzy:
Chellali, Mustapha
Meddah, Nacéra
Powiązania:
https://bibliotekanauki.pl/articles/743338.pdf
Data publikacji:
2012
Wydawca:
Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
Tematy:
2-domination number
2-independence number
trees
Opis:
Let G = (V,E) be a graph. A subset S of V is a 2-dominating set if every vertex of V-S is dominated at least 2 times, and S is a 2-independent set of G if every vertex of S has at most one neighbor in S. The minimum cardinality of a 2-dominating set a of G is the 2-domination number γ₂(G) and the maximum cardinality of a 2-independent set of G is the 2-independence number β₂(G). Fink and Jacobson proved that γ₂(G) ≤ β₂(G) for every graph G. In this paper we provide a constructive characterization of trees with equal 2-domination and 2-independence numbers.
Źródło:
Discussiones Mathematicae Graph Theory; 2012, 32, 2; 263-270
2083-5892
Pojawia się w:
Discussiones Mathematicae Graph Theory
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Domination Number, Independent Domination Number and 2-Independence Number in Trees
Autorzy:
Dehgardi, Nasrin
Sheikholeslami, Seyed Mahmoud
Valinavaz, Mina
Aram, Hamideh
Volkmann, Lutz
Powiązania:
https://bibliotekanauki.pl/articles/32083746.pdf
Data publikacji:
2021-02-01
Wydawca:
Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
Tematy:
2-independence number
domination number
independent domination number
Opis:
For a graph $G$, let $\gamma(G)$ be the domination number, $i(G)$ be the independent domination number and $\beta_2(G)$ be the 2-independence number. In this paper, we prove that for any tree $T$ of order $n ≥ 2, 4\beta_2(T) − 3\gamma(T) ≥ 3i(T)$, and we characterize all trees attaining equality. Also we prove that for every tree $T$ of order \(n ≥ 2, i(T)≤\frac{3\beta_2(T)}{4}\), and we characterize all extreme trees.
Źródło:
Discussiones Mathematicae Graph Theory; 2021, 41, 1; 39-49
2083-5892
Pojawia się w:
Discussiones Mathematicae Graph Theory
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Chvátal-Erdös type theorems
Autorzy:
Faudree, Jill
Faudree, Ralph
Gould, Ronald
Jacobson, Michael
Magnant, Colton
Powiązania:
https://bibliotekanauki.pl/articles/744255.pdf
Data publikacji:
2010
Wydawca:
Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
Tematy:
Hamiltonian
Hamiltonian-connected
Chvátal-Erdös condition
independence number
Opis:
The Chvátal-Erdös theorems imply that if G is a graph of order n ≥ 3 with κ(G) ≥ α(G), then G is hamiltonian, and if κ(G) > α(G), then G is hamiltonian-connected. We generalize these results by replacing the connectivity and independence number conditions with a weaker minimum degree and independence number condition in the presence of sufficient connectivity. More specifically, it is noted that if G is a graph of order n and k ≥ 2 is a positive integer such that κ(G) ≥ k, δ(G) > (n+k²-k)/(k+1), and δ(G) ≥ α(G)+k-2, then G is hamiltonian. It is shown that if G is a graph of order n and k ≥ 3 is a positive integer such that κ(G) ≥ 4k²+1, δ(G) > (n+k²-2k)/k, and δ(G) ≥ α(G)+k-2, then G is hamiltonian-connected. This result supports the conjecture that if G is a graph of order n and k ≥ 3 is a positive integer such that κ(G) ≥ k, δ(G) > (n+k²-2k)/k, and δ(G) ≥ α(G)+k-2, then G is hamiltonian-connected, and the conjecture is verified for k = 3 and 4.
Źródło:
Discussiones Mathematicae Graph Theory; 2010, 30, 2; 245-256
2083-5892
Pojawia się w:
Discussiones Mathematicae Graph Theory
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
On Selkow’s Bound on the Independence Number of Graphs
Autorzy:
Harant, Jochen
Mohr, Samuel
Powiązania:
https://bibliotekanauki.pl/articles/31343349.pdf
Data publikacji:
2019-08-01
Wydawca:
Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
Tematy:
graph
independence number
Opis:
For a graph $G$ with vertex set $ V (G) $ and independence number $ \alpha (G) $, Selkow [A Probabilistic lower bound on the independence number of graphs, Discrete Math. 132 (1994) 363–365] established the famous lower bound \( \sum_{ v \in V (G) } \tfrac{1}{d(v)+1} ( 1+ \max \{ \tfrac{ d(v) }{ d(v)+1 } - \sum_{ u \in N(v) } \tfrac{1}{ d(u)+1 },0 \} ) \) on $ \alpha (G) $, where $ N(v) $ and $ d(v) = | N(v) | $ denote the neighborhood and the degree of a vertex $ v \in V (G) $, respectively. However, Selkow’s original proof of this result is incorrect. We give a new probabilistic proof of Selkow’s bound here.
Źródło:
Discussiones Mathematicae Graph Theory; 2019, 39, 3; 655-657
2083-5892
Pojawia się w:
Discussiones Mathematicae Graph Theory
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Extending the MAX Algorithm for Maximum Independent Set
Autorzy:
Lê, Ngoc C.
Brause, Christoph
Schiermeyer, Ingo
Powiązania:
https://bibliotekanauki.pl/articles/31339469.pdf
Data publikacji:
2015-05-01
Wydawca:
Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
Tematy:
maximum independent set
stable set
stability number
independence number
reduction
graph transformation
MAX Algorithm
MIN Algorithm
Vertex Order Algorithm
Opis:
The maximum independent set problem is an NP-hard problem. In this paper, we consider Algorithm MAX, which is a polynomial time algorithm for finding a maximal independent set in a graph G. We present a set of forbidden induced subgraphs such that Algorithm MAX always results in finding a maximum independent set of G. We also describe two modifications of Algorithm MAX and sets of forbidden induced subgraphs for the new algorithms.
Źródło:
Discussiones Mathematicae Graph Theory; 2015, 35, 2; 365-386
2083-5892
Pojawia się w:
Discussiones Mathematicae Graph Theory
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
A note of arbitrarily vertex decomposable graphs
Autorzy:
Marczyk, A.
Powiązania:
https://bibliotekanauki.pl/articles/254919.pdf
Data publikacji:
2006
Wydawca:
Akademia Górniczo-Hutnicza im. Stanisława Staszica w Krakowie. Wydawnictwo AGH
Tematy:
arbitrarily vertex decomposable graphs
traceable graphs
independence number
perfect matching
Opis:
A graph G of order n is said to be arbitrarily vertex decomposable if for each sequence (n1,..., nk) of positive integers such that n1 + ... + nk = n there exists a partition (V1,..., Vk) of the vertex set of G such that for each i ∈ {1,..., k}, Vi induces a connected subgraph of G on ni vertices. In this paper we show that if G is a two-connected graph on n vertices with the independence number at most ⌈n/2⌉ and such that the degree sum of any pair of non-adjacent vertices is at least n - 3, then G is arbitrarily vertex decomposable. We present another result for connected graphs satisfying a similar condition, where the bound n - 3 is replaced by n - 2.
Źródło:
Opuscula Mathematica; 2006, 26, 1; 109-118
1232-9274
2300-6919
Pojawia się w:
Opuscula Mathematica
Dostawca treści:
Biblioteka Nauki
Artykuł
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