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Wyświetlanie 1-15 z 15
Tytuł:
Further Results on Packing Related Parameters in Graphs
Autorzy:
Mojdeh, Doost Ali
Samadi, Babak
Yero, Ismael G.
Powiązania:
https://bibliotekanauki.pl/articles/32361731.pdf
Data publikacji:
2022-05-01
Wydawca:
Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
Tematy:
packing number
open packing number
independence number
Nordhaus-Gaddum inequality
total domination number
Opis:
Given a graph G = (V, E), a set B ⊆ V (G) is a packing in G if the closed neighborhoods of every pair of distinct vertices in B are pairwise disjoint. The packing number ρ(G) of G is the maximum cardinality of a packing in G. Similarly, open packing sets and open packing number are defined for a graph G by using open neighborhoods instead of closed ones. We give several results concerning the (open) packing number of graphs in this paper. For instance, several bounds on these packing parameters along with some Nordhaus-Gaddum inequalities are given. We characterize all graphs with equal packing and independence numbers and give the characterization of all graphs for which the packing number is equal to the independence number minus one. In addition, due to the close connection between the open packing and total domination numbers, we prove a new upper bound on the total domination number γt(T) for a tree T of order n ≥ 2 improving the upper bound γt(T) ≤ (n + s)/2 given by Chellali and Haynes in 2004, in which s is the number of support vertices of T.
Źródło:
Discussiones Mathematicae Graph Theory; 2022, 42, 2; 333-348
2083-5892
Pojawia się w:
Discussiones Mathematicae Graph Theory
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
More on the Rainbow Disconnection in Graphs
Autorzy:
Bai, Xuqing
Chang, Renying
Huang, Zhong
Li, Xueliang
Powiązania:
https://bibliotekanauki.pl/articles/32222544.pdf
Data publikacji:
2022-11-01
Wydawca:
Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
Tematy:
edge-coloring
edge-connectivity
rainbow disconnection coloring (number)
Erdős-Gallai type problem
Nordhaus-Gaddum type bounds
complexity
NP-hard (complete)
Opis:
Let G be a nontrivial edge-colored connected graph. An edge-cut R of G is called a rainbow-cut if no two of its edges are colored the same. An edge-colored graph G is rainbow disconnected if for every two vertices u and v of G, there exists a u-v-rainbow-cut separating them. For a connected graph G, the rainbow disconnection number of G, denoted by rd(G), is defined as the smallest number of colors that are needed in order to make G rainbow disconnected. In this paper, we first determine the maximum size of a connected graph G of order n with rd(G) = k for any given integers k and n with 1 ≤ k ≤ n − 1, which solves a conjecture posed only for n odd in [G. Chartrand, S. Devereaux, T.W. Haynes, S.T. Hedetniemi and P. Zhang, Rainbow disconnection in graphs, Discuss. Math. Graph Theory 38 (2018) 1007–1021]. From this result and a result in their paper, we obtain Erdős-Gallai type results for rd(G). Secondly, we discuss bounds on rd(G) for complete multipartite graphs, critical graphs with respect to the chromatic number, minimal graphs with respect to the chromatic index, and regular graphs, and we also give the values of rd(G) for several special graphs. Thirdly, we get Nordhaus-Gaddum type bounds for rd(G), and examples are given to show that the upper and lower bounds are sharp. Finally, we show that for a connected graph G, to compute rd(G) is NP-hard. In particular, we show that it is already NP-complete to decide if rd(G) = 3 for a connected cubic graph. Moreover, we show that for a given edge-colored (with an unbounded number of colors) connected graph G it is NP-complete to decide whether G is rainbow disconnected.
Źródło:
Discussiones Mathematicae Graph Theory; 2022, 42, 4; 1185-1204
2083-5892
Pojawia się w:
Discussiones Mathematicae Graph Theory
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Nordhaus-Gaddum bounds for upper total domination
Autorzy:
Haynes, Teresa W.
Henning, Michael A.
Powiązania:
https://bibliotekanauki.pl/articles/2216175.pdf
Data publikacji:
2022
Wydawca:
Akademia Górniczo-Hutnicza im. Stanisława Staszica w Krakowie. Wydawnictwo AGH
Tematy:
upper total domination
Nordhaus-Gaddum bound
Opis:
A set S of vertices in an isolate-free graph G is a total dominating set if every vertex in G is adjacent to a vertex in S. A total dominating set of G is minimal if it contains no total dominating set of $\bar{G}$ as a proper subset. The upper total domination number $Γ_t(G)$ of G is the maximum cardinality of a minimal total dominating set in G. We establish Nordhaus-Gaddum bounds involving the upper total domination numbers of a graph G and its complement $\bar{G}$. We prove that if G is a graph of order n such that both G and $\bar{G}$ are isolate-free, then $Γ_t(G) + Γ_t(\bar{G}) ≤ n + 2$ and $Γ_t(G)Γ_t(\bar{G}) ≤ 1/4 (n + 2)^2$, and these bounds are tight.
Źródło:
Opuscula Mathematica; 2022, 42, 4; 573-582
1232-9274
2300-6919
Pojawia się w:
Opuscula Mathematica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Remarks on the outer-independent double Italian domination number
Autorzy:
Volkman, Lutz
Powiązania:
https://bibliotekanauki.pl/articles/2051048.pdf
Data publikacji:
2021
Wydawca:
Akademia Górniczo-Hutnicza im. Stanisława Staszica w Krakowie. Wydawnictwo AGH
Tematy:
double Italian domination number
outer-independent double Italian domination number
Nordhaus-Gaddum bound
Opis:
Let $G$ be a graph with vertex set $V(G)$. If $u \in V(G)$, then $N[u]$ is the closed neighborhood of $u$. An outer-independent double Italian dominating function (OIDIDF) on a graph $G$ is a function $ƒ : V(G) \rightarrow \{0, 1, 2, 3\}$ such that if $ƒ (v) \in \{0, 1\}$ for a vertex $v \in V(G)$, then $\Sigma_{x \in N[v]} f(x) \geq 3$, and the set ${u \in V(G) : f (u) = 0}$ is independent. The weight of an OIDIDF $f$ is the sum $\Sigma_{v \in V(G)} f(v)$. The outer-independent double Italian domination number $\gamma_{oidI}(G)$ equals the minimum weight of an OIDIDF on G. In this paper we present Nordhaus-Gaddum type bounds on the outer-independent double Italian domination number which improved corresponding results given in [F. Azvin, N. Jafari Rad, L. Volkmann, \textit{Bounds on the outer-independent double Italian domination number}, Commun. Comb. Optim. 6 (2021), 123-136]. Furthermore, we determine the outer-independent double Italian domination number of some families of graphs.
Źródło:
Opuscula Mathematica; 2021, 41, 2; 259-268
1232-9274
2300-6919
Pojawia się w:
Opuscula Mathematica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Triameter of Graphs
Autorzy:
Das, Angsuman
Powiązania:
https://bibliotekanauki.pl/articles/32083897.pdf
Data publikacji:
2021-05-01
Wydawca:
Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
Tematy:
distance
radio k -coloring
Nordhaus-Gaddum bounds
Opis:
In this paper, we study a new distance parameter triameter of a connected graph G, which is defined as max{d(u; v)+d(v;w)+d(u;w) : u; v;w ∈ V} and is denoted by tr(G). We find various upper and lower bounds on tr(G) in terms of order, girth, domination parameters etc., and characterize the graphs attaining those bounds. In the process, we provide some lower bounds of (connected, total) domination numbers of a connected graph in terms of its triameter. The lower bound on total domination number was proved earlier by Henning and Yeo. We provide a shorter proof of that. Moreover, we prove Nordhaus-Gaddum type bounds on tr(G) and find tr(G) for some specific family of graphs.
Źródło:
Discussiones Mathematicae Graph Theory; 2021, 41, 2; 601-616
2083-5892
Pojawia się w:
Discussiones Mathematicae Graph Theory
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Extremal Graphs for a Bound on the Roman Domination Number
Autorzy:
Bouchou, Ahmed
Blidia, Mostafa
Chellali, Mustapha
Powiązania:
https://bibliotekanauki.pl/articles/31513493.pdf
Data publikacji:
2020-08-01
Wydawca:
Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
Tematy:
Roman domination
Roman domination number
Nordhaus-Gaddum inequalities
Opis:
A Roman dominating function on a graph G = (V, E) is a function f:V (G) → {0, 1, 2} such that every vertex u for which f(u) = 0 is adjacent to at least one vertex v with f(v) = 2. The weight of a Roman dominating function is the value w(f) = Σu∈V(G) f(u). The minimum weight of a Roman dominating function on a graph G is called the Roman domination number of G, denoted by γR(G). In 2009, Chambers, Kinnersley, Prince and West proved that for any graph G with n vertices and maximum degree Δ, γR(G) ≤ n + 1 − Δ. In this paper, we give a characterization of graphs attaining the previous bound including trees, regular and semiregular graphs. Moreover, we prove that the problem of deciding whether γR(G) = n + 1 − Δ is co-complete. Finally, we provide a characterization of extremal graphs of a Nordhaus–Gaddum bound for γR(G) + γR (Ḡ), where Ḡ is the complement graph of G.
Źródło:
Discussiones Mathematicae Graph Theory; 2020, 40, 3; 771-785
2083-5892
Pojawia się w:
Discussiones Mathematicae Graph Theory
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
A Note on Roman Domination of Digraphs
Autorzy:
Chen, Xiaodan
Hao, Guoliang
Xie, Zhihong
Powiązania:
https://bibliotekanauki.pl/articles/31343785.pdf
Data publikacji:
2019-02-01
Wydawca:
Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
Tematy:
Roman domination number
domination number
digraph
Nordhaus-Gaddum
Opis:
A vertex subset $S$ of a digraph $D$ is called a dominating set of $D$ if every vertex not in $S$ is adjacent from at least one vertex in $S$. The domination number of a digraph $D$, denoted by $ \gamma(D) $, is the minimum cardinality of a dominating set of $D$. A Roman dominating function (RDF) on a digraph $D$ is a function $ f : V (D) \rightarrow {0, 1, 2} $ satisfying the condition that every vertex $v$ with $f(v) = 0$ has an in-neighbor $u$ with $f(u) = 2$. The weight of an RDF $f$ is the value $ \omega (f) = \Sigma_{ v \in V(D) } f(v) $. The Roman domination number of a digraph $D$, denoted by $ \gamma_R (D) $, is the minimum weight of an RDF on $D$. In this paper, for any integer $k$ with $ 2 \le k \le \gamma(D) $, we characterize the digraphs $D$ of order $ n \ge 4 $ with $ \delta − (D) \ge 1 $ for which $ \gamma_R(D) = (D) + k $ holds. We also characterize the digraphs $D$ of order $ n \ge k $ with $ \gamma_R(D) = k $ for any positive integer $k$. In addition, we present a Nordhaus-Gaddum bound on the Roman domination number of digraphs.
Źródło:
Discussiones Mathematicae Graph Theory; 2019, 39, 1; 13-21
2083-5892
Pojawia się w:
Discussiones Mathematicae Graph Theory
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Nordhaus-Gaddum-Type Results for Resistance Distance-Based Graph Invariants
Autorzy:
Das, Kinkar Ch.
Yang, Yujun
Xu, Kexiang
Powiązania:
https://bibliotekanauki.pl/articles/31340811.pdf
Data publikacji:
2016-08-01
Wydawca:
Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
Tematy:
resistance distance
Kirchhoff index
additive degree-Kirchhoff index
multiplicative degree-Kirchhoff index
Nordhaus-Gaddum-type result
Opis:
Two decades ago, resistance distance was introduced to characterize “chemical distance” in (molecular) graphs. In this paper, we consider three resistance distance-based graph invariants, namely, the Kirchhoff index, the additive degree-Kirchhoff index, and the multiplicative degree-Kirchhoff index. Some Nordhaus-Gaddum-type results for these three molecular structure descriptors are obtained. In addition, a relation between these Kirchhoffian indices is established.
Źródło:
Discussiones Mathematicae Graph Theory; 2016, 36, 3; 695-707
2083-5892
Pojawia się w:
Discussiones Mathematicae Graph Theory
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
The Vertex-Rainbow Index of A Graph
Autorzy:
Mao, Yaping
Powiązania:
https://bibliotekanauki.pl/articles/31340818.pdf
Data publikacji:
2016-08-01
Wydawca:
Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
Tematy:
vertex-coloring
connectivity
vertex-rainbow S-tree
vertex- rainbow index
Nordhaus-Gaddum type
Opis:
The k-rainbow index rxk(G) of a connected graph G was introduced by Chartrand, Okamoto and Zhang in 2010. As a natural counterpart of the k-rainbow index, we introduce the concept of k-vertex-rainbow index rvxk(G) in this paper. In this paper, sharp upper and lower bounds of rvxk(G) are given for a connected graph G of order n, that is, 0 ≤ rvxk(G) ≤ n − 2. We obtain Nordhaus-Gaddum results for 3-vertex-rainbow index of a graph G of order n, and show that rvx3(G) + rvx3(Ḡ) = 4 for n = 4 and 2 ≤ rvx3(G) + rvx3(Ḡ) ≤ n − 1 for n ≥ 5. Let t(n, k, ℓ) denote the minimal size of a connected graph G of order n with rvxk(G) ≤ ℓ, where 2 ≤ ℓ ≤ n − 2 and 2 ≤ k ≤ n. Upper and lower bounds on t(n, k, ℓ) are also obtained.
Źródło:
Discussiones Mathematicae Graph Theory; 2016, 36, 3; 669-681
2083-5892
Pojawia się w:
Discussiones Mathematicae Graph Theory
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Various Bounds for Liar’s Domination Number
Autorzy:
Alimadadi, Abdollah
Mojdeh, Doost Ali
Rad, Nader Jafari
Powiązania:
https://bibliotekanauki.pl/articles/31340859.pdf
Data publikacji:
2016-08-01
Wydawca:
Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
Tematy:
liar’s domination
diameter
regular graph
Nordhaus-Gaddum
Opis:
Let $ G = (V,E) $ be a graph. A set $ S \subseteq V $ is a dominating set if \( \bigcup_{v \in S} N[v] = V \), where $ N[v] $ is the closed neighborhood of $ v $. Let $ L \subseteq V $ be a dominating set, and let $v$ be a designated vertex in $V$ (an intruder vertex). Each vertex in $ L \cap N[v] $ can report that $v$ is the location of the intruder, but (at most) one $ x \in L \cap N[v] $ can report any $ w \in N[x] $ as the intruder location or $ x $ can indicate that there is no intruder in $ N[x] $. A dominating set $L$ is called a liar’s dominating set if every $ v \in V (G) $ can be correctly identified as an intruder location under these restrictions. The minimum cardinality of a liar’s dominating set is called the liar’s domination number, and is denoted by $ \gamma_{LR} (G) $. In this paper, we present sharp bounds for the liar’s domination number in terms of the diameter, the girth and clique covering number of a graph. We present two Nordhaus-Gaddum type relations for $ \gamma_{LR} (G) $, and study liar’s dominating set sensitivity versus edge-connectivity. We also present various bounds for the liar’s domination component number, that is, the maximum number of components over all minimum liar’s dominating sets.
Źródło:
Discussiones Mathematicae Graph Theory; 2016, 36, 3; 629-641
2083-5892
Pojawia się w:
Discussiones Mathematicae Graph Theory
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Bounds on the Signed 2-Independence Number in Graphs
Autorzy:
Volkmann, Lutz
Powiązania:
https://bibliotekanauki.pl/articles/29794119.pdf
Data publikacji:
2013-09-01
Wydawca:
Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
Tematy:
bounds
signed 2-independence function
signed 2-independence number
Nordhaus-Gaddum type result
Opis:
Let $G$ be a finite and simple graph with vertex set $V (G)$, and let $f V (G) → {−1, 1}$ be a two-valued function. If $∑_{x∈N|v|} f(x) ≤ 1$ for each $v ∈ V (G)$, where $N[v]$ is the closed neighborhood of $v$, then $f$ is a signed 2-independence function on $G$. The weight of a signed 2-independence function $f$ is $w(f) = ∑_{v∈V (G)} f(v)$. The maximum of weights $w(f)$, taken over all signed 2-independence functions $f$ on $G$, is the signed 2-independence number $α_s^2(G)$ of $G$. In this work, we mainly present upper bounds on $α_s^2(G)$, as for example $α_s^2(G) ≤ n−2 [∆ (G)//2]$, and we prove the Nordhaus-Gaddum type inequality $α_s^2 (G) + α_s^2(G) ≤ n+1$, where $n$ is the order and $∆ (G)$ is the maximum degree of the graph $G$. Some of our theorems improve well-known results on the signed 2-independence number.
Źródło:
Discussiones Mathematicae Graph Theory; 2013, 33, 4; 709-715
2083-5892
Pojawia się w:
Discussiones Mathematicae Graph Theory
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Some Sharp Bounds on the Negative Decision Number of Graphs
Autorzy:
Liang, Hongyu
Powiązania:
https://bibliotekanauki.pl/articles/29785048.pdf
Data publikacji:
2013-09-01
Wydawca:
Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
Tematy:
negative decision number
bad function
sharp upper bounds
Nordhaus-Gaddum results
Opis:
Let $G = (V,E)$ be a graph. A function $f : V → {-1,1}$ is called a bad function of $G$ if $∑_{u∈N_G(v)} f(u) ≤ 1$ for all $v ∈ V$ where $N_G(v)$ denotes the set of neighbors of $v$ in $G$. The negative decision number of $G$, introduced in [12], is the maximum value of $∑_{v∈V} f(v)$ taken over all bad functions of $G$. In this paper, we present sharp upper bounds on the negative decision number of a graph in terms of its order, minimum degree, and maximum degree. We also establish a sharp Nordhaus-Gaddum-type inequality for the negative decision number.
Źródło:
Discussiones Mathematicae Graph Theory; 2013, 33, 4; 649-656
2083-5892
Pojawia się w:
Discussiones Mathematicae Graph Theory
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
On the hat problem on a graph
Autorzy:
Krzywkowski, M.
Powiązania:
https://bibliotekanauki.pl/articles/256048.pdf
Data publikacji:
2012
Wydawca:
Akademia Górniczo-Hutnicza im. Stanisława Staszica w Krakowie. Wydawnictwo AGH
Tematy:
hat problem
graph
degree
neighborhood
neighborhood-dominated
unicyclic
universal vertex
Nordhaus-Gaddum
Opis:
The topic of this paper is the hat problem in which each of n players is uniformly and independently fitted with a blue or red hat. Then everybody can try to guess simultaneously his own hat color by looking at the hat colors of the other players. The team wins if at least one player guesses his hat color correctly, and no one guesses his hat color wrong; otherwise the team loses. The aim is to maximize the probability of winning. In this version every player can see everybody excluding himself. We consider such a problem on a graph, where vertices correspond to players, and a player can see each player to whom he is connected by an edge. The solution of the hat problem on a graph is known for trees and for cycles on four or at least nine vertices. In this paper first we give an upper bound on the maximum chance of success for graphs with neighborhood-dominated vertices. Next we solve the problem on unicyclic graphs containing a cycle on at least nine vertices. We prove that the maximum chance of success is one by two. Then we consider the hat problem on a graph with a universal vertex. We prove that there always exists an optimal strategy such that in every case some vertex guesses its color. Moreover, we prove that there exists a graph with a universal vertex for which there exists an optimal strategy such that in some case no vertex guesses its color. We also give some Nordhaus-Gaddum type inequalities.
Źródło:
Opuscula Mathematica; 2012, 32, 2; 285-296
1232-9274
2300-6919
Pojawia się w:
Opuscula Mathematica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Nordhaus-Gaddum results for weakly convex domination number of a graph
Autorzy:
Lemańska, Magdalena
Powiązania:
https://bibliotekanauki.pl/articles/744253.pdf
Data publikacji:
2010
Wydawca:
Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
Tematy:
weakly convex domination number
Nordhaus-Gaddum results
Opis:
Nordhaus-Gaddum results for weakly convex domination number of a graph G are studied.
Źródło:
Discussiones Mathematicae Graph Theory; 2010, 30, 2; 257-263
2083-5892
Pojawia się w:
Discussiones Mathematicae Graph Theory
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Generalised irredundance in graphs: Nordhaus-Gaddum bounds
Autorzy:
Cockayne, Ernest
Finbow, Stephen
Powiązania:
https://bibliotekanauki.pl/articles/744461.pdf
Data publikacji:
2004
Wydawca:
Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
Tematy:
graph
generalised irredundance
Nordhaus-Gaddum
Opis:
For each vertex s of the vertex subset S of a simple graph G, we define Boolean variables p = p(s,S), q = q(s,S) and r = r(s,S) which measure existence of three kinds of S-private neighbours (S-pns) of s. A 3-variable Boolean function f = f(p,q,r) may be considered as a compound existence property of S-pns. The subset S is called an f-set of G if f = 1 for all s ∈ S and the class of f-sets of G is denoted by $Ω_f(G)$. Only 64 Boolean functions f can produce different classes $Ω_f(G)$, special cases of which include the independent sets, irredundant sets, open irredundant sets and CO-irredundant sets of G. Let $Q_f(G)$ be the maximum cardinality of an f-set of G. For each of the 64 functions f, we establish sharp upper bounds for the sum $Q_f(G) + Q_f(G̅)$ and the product $Q_f(G)Q_f(G̅)$ in terms of n, the order of G.
Źródło:
Discussiones Mathematicae Graph Theory; 2004, 24, 1; 147-160
2083-5892
Pojawia się w:
Discussiones Mathematicae Graph Theory
Dostawca treści:
Biblioteka Nauki
Artykuł
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