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Wyświetlanie 1-8 z 8
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:
The Roman Domatic Problem in Graphs and Digraphs: A Survey
Autorzy:
Chellali, Mustapha
Rad, Nader Jafari
Sheikholeslami, Seyed Mahmoud
Volkmann, Lutz
Powiązania:
https://bibliotekanauki.pl/articles/32304148.pdf
Data publikacji:
2022-08-01
Wydawca:
Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
Tematy:
Roman domination
domatic
Opis:
In this paper, we survey results on the Roman domatic number and its variants in both graphs and digraphs. This fifth survey completes our works on Roman domination and its variations published in two book chapters and two other surveys.
Źródło:
Discussiones Mathematicae Graph Theory; 2022, 42, 3; 861-891
2083-5892
Pojawia się w:
Discussiones Mathematicae Graph Theory
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
On The Co-Roman Domination in Graphs
Autorzy:
Shao, Zehui
Sheikholeslami, Seyed Mahmoud
Soroudi, Marzieh
Volkmann, Lutz
Liu, Xinmiao
Powiązania:
https://bibliotekanauki.pl/articles/31343438.pdf
Data publikacji:
2019-05-01
Wydawca:
Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
Tematy:
co-Roman dominating function
co-Roman domination number
Roman domination
Opis:
Let $G = (V, E)$ be a graph and let $f : V (G) \rightarrow {0, 1, 2}$ be a function. A vertex $v$ is said to be protected with respect to $f$, if $f(v) > 0$ or $f(v) = 0$ and $v$ is adjacent to a vertex of positive weight. The function $f$ is a co-Roman dominating function if (i) every vertex in $V$ is protected, and (ii) each $ v \in V $ with positive weight has a neighbor $ u \in V $ with $ f(u) = 0 $ such that the function $ f_{uv} : V \rightarrow {0, 1, 2} $, defined by $ f_{uv} (u) = 1$, $ f_{uv}(v) = f(v) − 1$ and $ f_{uv}(x) = f(x)$ for $ x \in V \backslash \{ v, u \} $, has no unprotected vertex. The weight of $f$ is $ \omega(f) = \Sigma_{ v \in V } f(v) $. The co-Roman domination number of a graph $G$, denoted by $ \gamma_{cr}(G) $, is the minimum weight of a co-Roman dominating function on $G$. In this paper, we give a characterization of graphs of order $n$ for which co-Roman domination number is \( \tfrac{2n}{3} \) or $n − 2$, which settles two open problem in [S. Arumugam, K. Ebadi and M. Manrique, Co-Roman domination in graphs, Proc. Indian Acad. Sci. Math. Sci. 125 (2015) 1–10]. Furthermore, we present some sharp bounds on the co-Roman domination number.
Źródło:
Discussiones Mathematicae Graph Theory; 2019, 39, 2; 455-472
2083-5892
Pojawia się w:
Discussiones Mathematicae Graph Theory
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
The Distance Roman Domination Numbers of Graphs
Autorzy:
Aram, Hamideh
Norouzian, Sepideh
Sheikholeslami, Seyed Mahmoud
Powiązania:
https://bibliotekanauki.pl/articles/30098151.pdf
Data publikacji:
2013-09-01
Wydawca:
Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
Tematy:
k-distance Roman dominating function
k-distance Roman domination number
Roman dominating function
Roman domination number
Opis:
Let $ k $ be a positive integer, and let $ G $ be a simple graph with vertex set $ V (G) $. A k-distance Roman dominating function on $ G $ is a labeling $ f : V (G) → {0, 1, 2} $ such that for every vertex with label 0, there is a vertex with label 2 at distance at most $ k $ from each other. The weight of a $k$-distance Roman dominating function $ f $ is the value $ \omega (f) =∑_{v∈V} f(v) $. The k-distance Roman domination number of a graph $G$, denoted by $\gamma_R^k (D) $, equals the minimum weight of a $k$-distance Roman dominating function on G. Note that the 1-distance Roman domination number $ \gamma_R^1 (G) $ is the usual Roman domination number $ \gamma_R (G) $. In this paper, we investigate properties of the $k$-distance Roman domination number. In particular, we prove that for any connected graph $ G $ of order $ n \geq k +2$, $\gamma_R^k (G) \leq 4n//(2k +3) $ and we characterize all graphs that achieve this bound. Some of our results extend these ones given by Cockayne et al. in 2004 and Chambers et al. in 2009 for the Roman domination number.
Źródło:
Discussiones Mathematicae Graph Theory; 2013, 33, 4; 717-730
2083-5892
Pojawia się w:
Discussiones Mathematicae Graph Theory
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
On The Total Roman Domination in Trees
Autorzy:
Amjadi, Jafar
Sheikholeslami, Seyed Mahmoud
Soroudi, Marzieh
Powiązania:
https://bibliotekanauki.pl/articles/31343413.pdf
Data publikacji:
2019-05-01
Wydawca:
Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
Tematy:
total Roman dominating function
total Roman domination number
trees
Opis:
A total Roman dominating function on a graph G is a function f : V (G) → {0, 1, 2} satisfying the following conditions: (i) every vertex u for which f(u) = 0 is adjacent to at least one vertex v for which f(v) = 2 and (ii) the subgraph of G induced by the set of all vertices of positive weight has no isolated vertex. The weight of a total Roman dominating function f is the value f(V (G)) = Σu∈V(G) f(u). The total Roman domination number γtR(G) is the minimum weight of a total Roman dominating function of G. Ahangar et al. in [H.A. Ahangar, M.A. Henning, V. Samodivkin and I.G. Yero, Total Roman domination in graphs, Appl. Anal. Discrete Math. 10 (2016) 501–517] recently showed that for any graph G without isolated vertices, 2γ(G) ≤ γtR(G) ≤ 3γ(G), where γ(G) is the domination number of G, and they raised the problem of characterizing the graphs G achieving these upper and lower bounds. In this paper, we provide a constructive characterization of these trees.
Źródło:
Discussiones Mathematicae Graph Theory; 2019, 39, 2; 519-532
2083-5892
Pojawia się w:
Discussiones Mathematicae Graph Theory
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Signed Total Roman Edge Domination In Graphs
Autorzy:
Asgharsharghi, Leila
Sheikholeslami, Seyed Mahmoud
Powiązania:
https://bibliotekanauki.pl/articles/31341578.pdf
Data publikacji:
2017-11-27
Wydawca:
Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
Tematy:
signed total Roman dominating function
signed total Roman domination number
signed total Roman edge dominating function
signed total Roman edge domination number
Opis:
Let $ G = (V,E) $ be a simple graph with vertex set $V$ and edge set $E$. A signed total Roman edge dominating function of $G$ is a function $ f : E \rightarrow {−1, 1, 2} $ satisfying the conditions that (i) $ \Sigma_{e^′ \in N(e)} f(e^′) \ge 1 $ for each $ e \in E $, where $N(e)$ is the open neighborhood of $e$, and (ii) every edge $e$ for which $f(e) = −1$ is adjacent to at least one edge $ e^′$ for which $f(e^′) = 2$. The weight of a signed total Roman edge dominating function $f$ is $ \omega(f) = \Sigma_{e \in E } f(e) $. The signed total Roman edge domination number $ \gamma_{stR}^' (G) $ of $G$ is the minimum weight of a signed total Roman edge dominating function of $G$. In this paper, we first prove that for every tree $T$ of order $ n \ge 4 $, $ \gamma_{stR}^' (T) \ge \frac{17−2n}{5} $ and we characterize all extreme trees, and then we present some sharp bounds for the signed total Roman edge domination number. We also determine this parameter for some classes of graphs.
Źródło:
Discussiones Mathematicae Graph Theory; 2017, 37, 4; 1039-1053
2083-5892
Pojawia się w:
Discussiones Mathematicae Graph Theory
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Signed Roman Edge k -Domination in Graphs
Autorzy:
Asgharsharghi, Leila
Sheikholeslami, Seyed Mahmoud
Volkmann, Lutz
Powiązania:
https://bibliotekanauki.pl/articles/31342188.pdf
Data publikacji:
2017-02-01
Wydawca:
Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
Tematy:
signed Roman edge k -dominating function
signed Roman edge k -domination number
Opis:
Let $ k \ge 1 $ be an integer, and $ G = (V, E) $ be a finite and simple graph. The closed neighborhood $ N_G [e]$ of an edge $e$ in a graph $G$ is the set consisting of $e$ and all edges having a common end-vertex with $e$. A signed Roman edge $k$-dominating function (SREkDF) on a graph $G$ is a function $ f : E \rightarrow {−1, 1, 2} $ satisfying the conditions that (i) for every edge $e$ of $G$, $ \Sigma_{ x \in N_G [e] } f(x) \ge k $ and (ii) every edge e for which $f(e) = −1$ is adjacent to at least one edge $ e^′ $ for which $ f(e^′) = 2 $. The minimum of the values $ \Sigma_{e \in E} f(e) $, taken over all signed Roman edge $k$-dominating functions $f$ of $G$ is called the signed Roman edge $k$-domination number of $G$, and is denoted by $ \gamma_{sRk}^' (G) $. In this paper we initiate the study of the signed Roman edge $k$-domination in graphs and present some (sharp) bounds for this parameter.
Źródło:
Discussiones Mathematicae Graph Theory; 2017, 37, 1; 39-53
2083-5892
Pojawia się w:
Discussiones Mathematicae Graph Theory
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
The k-Rainbow Bondage Number of a Digraph
Autorzy:
Amjadi, Jafar
Mohammadi, Negar
Sheikholeslami, Seyed Mahmoud
Volkmann, Lutz
Powiązania:
https://bibliotekanauki.pl/articles/31339490.pdf
Data publikacji:
2015-05-01
Wydawca:
Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
Tematy:
k-rainbow dominating function
k-rainbow domination number
k-rainbow bondage number
digraph
Opis:
Let $ D = (V,A) $ be a finite and simple digraph. A $k$-rainbow dominating function ($ k \text{RDF} $) of a digraph $D$ is a function $f$ from the vertex set $V$ to the set of all subsets of the set ${1, 2, . . ., k}$ such that for any vertex $ v \in V $ with $ f(v) = \emptyset $ the condition \( \bigcup_{ u \in N^−(v) } f(u) = {1, 2, . . ., k} \) is fulfilled, where $ N^− (v) $ is the set of in-neighbors of $v$. The weight of a \( k \text{RDF} \) \( f \) is the value \( \omega (f) = \sum_{v \in V} |f(v)| \). The $k$-rainbow domination number of a digraph $D$, denoted by $ \gamma_{rk} (D) $, is the minimum weight of a $ k \text{RDF} $ of $D$. The $k$-rainbow bondage number $ b_{rk} (D) $ of a digraph $D$ with maximum in-degree at least two, is the minimum cardinality of all sets $ A^\prime \subseteq A $ for which $ \gamma_{rk} (D−A^\prime ) > \gamma_{rk} (D) $. In this paper, we establish some bounds for the $k$-rainbow bondage number and determine the $k$-rainbow bondage number of several classes of digraphs.
Źródło:
Discussiones Mathematicae Graph Theory; 2015, 35, 2; 261-270
2083-5892
Pojawia się w:
Discussiones Mathematicae Graph Theory
Dostawca treści:
Biblioteka Nauki
Artykuł
    Wyświetlanie 1-8 z 8

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