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    Wyświetlanie 1-11 z 11
    Tytuł:
    A New Upper Bound for the Perfect Italian Domination Number of a Tree
    Autorzy:
    Nazari-Moghaddam, Sakineh
    Chellali, Mustapha
    Powiązania:
    https://bibliotekanauki.pl/articles/32304138.pdf
    Data publikacji:
    2022-08-01
    Wydawca:
    Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
    Tematy:
    Italian domination
    Roman domination
    perfect Italian domination
    Opis:
    A perfect Italian dominating function (PIDF) on a graph $G$ is a function $ f : V (G) \rightarrow \{ 0, 1, 2 \} $ satisfying the condition that for every vertex u with $f(u) = 0$, the total weight of $f$ assigned to the neighbors of $u$ is exactly two. The weight of a PIDF is the sum of its functions values over all vertices. The perfect Italian domination number of $G$, denoted $ \gamma_I^p (G) $, is the minimum weight of a PIDF of $G$. In this paper, we show that for every tree $T$ of order $ n \ge 3 $, with $ \mathcal{l} (T) $ leaves and $s(T)$ support vertices, \( \gamma_I^p (T) \ge \tfrac {4n- \mathscr{l}(T) + 2s (T) - 1}{5} \), improving a previous bound given by T.W. Haynes and M.A. Henning in [Perfect Italian domination in trees, Discrete Appl. Math. 260 (2019) 164–177].
    Źródło:
    Discussiones Mathematicae Graph Theory; 2022, 42, 3; 1005-1022
    2083-5892
    Pojawia się w:
    Discussiones Mathematicae Graph Theory
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Some Progress on the Double Roman Domination in Graphs
    Autorzy:
    Rad, Nader Jafari
    Rahbani, Hadi
    Powiązania:
    https://bibliotekanauki.pl/articles/31343730.pdf
    Data publikacji:
    2019-02-01
    Wydawca:
    Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
    Tematy:
    Roman domination
    double Roman domination
    Opis:
    For a graph $ G = (V,E) $, a double Roman dominating function (or just DRDF) is a function $ f : V \rightarrow {0, 1, 2, 3} $ having the property that if $ f(v) = 0 $ for a vertex $ v $, then $ v $ has at least two neighbors assigned 2 under $ f $ or one neighbor assigned 3 under $ f $, and if $ f(v) = 1 $, then vertex $ v $ must have at least one neighbor $ w $ with $ f(w) \ge 2 $. The weight of a DRDF $f$ is the sum $f(V) = \Sigma_{ v \in V } f(v) $, and the minimum weight of a DRDF on $G$ is the double Roman domination number of $G$, denoted by $ \gamma_{dR} (G) $. In this paper, we derive sharp upper and lower bounds on $ \gamma_{dR} (G) + \gamma_{dR} ( \overline{G} ) $ and also $ \gamma_{dR} (G ) \gamma_{dR} ( \overline{G} ) $, where $ \overline{G} $ is the complement of graph $G$. We also show that the decision problem for the double Roman domination number is NP- complete even when restricted to bipartite graphs and chordal graphs.
    Źródło:
    Discussiones Mathematicae Graph Theory; 2019, 39, 1; 41-53
    2083-5892
    Pojawia się w:
    Discussiones Mathematicae Graph Theory
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Total Roman {2}-Dominating Functions in Graphs
    Autorzy:
    Ahangar, H. Abdollahzadeh
    Chellali, M.
    Sheikholeslami, S.M.
    Valenzuela-Tripodoro, J.C.
    Powiązania:
    https://bibliotekanauki.pl/articles/32304142.pdf
    Data publikacji:
    2022-08-01
    Wydawca:
    Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
    Tematy:
    Roman domination
    Roman {2}-domination
    total Roman {2}-domination
    Opis:
    A Roman {2}-dominating function (R2F) is a function f : V → {0, 1, 2} with the property that for every vertex v ∈ V with f(v) = 0 there is a neighbor u of v with f(u) = 2, or there are two neighbors x, y of v with f(x) = f(y) = 1. A total Roman {2}-dominating function (TR2DF) is an R2F f such that the set of vertices with f(v) > 0 induce a subgraph with no isolated vertices. The weight of a TR2DF is the sum of its function values over all vertices, and the minimum weight of a TR2DF of G is the total Roman {2}-domination number γtR2(G). In this paper, we initiate the study of total Roman {2}-dominating functions, where properties are established. Moreover, we present various bounds on the total Roman {2}-domination number. We also show that the decision problem associated with γtR2(G) is possible to compute this parameter in linear time for bounded clique-width graphs (including trees).
    Źródło:
    Discussiones Mathematicae Graph Theory; 2022, 42, 3; 937-958
    2083-5892
    Pojawia się w:
    Discussiones Mathematicae Graph Theory
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Relating 2-Rainbow Domination To Roman Domination
    Autorzy:
    Alvarado, José D.
    Dantas, Simone
    Rautenbach, Dieter
    Powiązania:
    https://bibliotekanauki.pl/articles/31341598.pdf
    Data publikacji:
    2017-11-27
    Wydawca:
    Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
    Tematy:
    2-rainbow domination
    Roman domination
    Opis:
    For a graph $G$, let $ \gamma_R (G)$ and $ \gamma_{r2} (G) $ denote the Roman domination number of $G$ and the 2-rainbow domination number of $G$, respectively. It is known that $ \gamma_{r2} (G) \le \gamma_R(G) \le 3/2 \gamma_{r2} (G) $. Fujita and Furuya [Difference between 2-rainbow domination and Roman domination in graphs, Discrete Appl. Math. 161 (2013) 806-812] present some kind of characterization of the graphs $G$ for which $ \gamma_R (G) − \gamma_{r2} (G) = k $ for some integer $k$. Unfortunately, their result does not lead to an algorithm that allows to recognize these graphs efficiently. We show that for every fixed non-negative integer $k$, the recognition of the connected $ K_4$-free graphs $G$ with $ \gamma_R (G) − \gamma_{r2} (G) = k $ is NP-hard, which implies that there is most likely no good characterization of these graphs. We characterize the graphs $ G $ such that $ \gamma_{r2} (H) = \gamma_R (H) $ for every induced subgraph $ H $ of $ G $, and collect several properties of the graphs $ G $ with $ \gamma_R (G) = 3/2 \gamma_{r2} (G) $.
    Źródło:
    Discussiones Mathematicae Graph Theory; 2017, 37, 4; 953-961
    2083-5892
    Pojawia się w:
    Discussiones Mathematicae Graph Theory
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Roman bondage in graphs
    Autorzy:
    Rad, Nader
    Volkmann, Lutz
    Powiązania:
    https://bibliotekanauki.pl/articles/743601.pdf
    Data publikacji:
    2011
    Wydawca:
    Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
    Tematy:
    domination
    Roman domination
    Roman bondage number
    Opis:
    A Roman dominating function on a graph G is a function f:V(G) → {0,1,2} satisfying the condition that every vertex u for which f(u) = 0 is adjacent to at least one vertex v for which f(v) = 2. The weight of a Roman dominating function is the value $f(V(G)) = ∑_{u ∈ V(G)}f(u)$. The Roman domination number, $γ_R(G)$, of G is the minimum weight of a Roman dominating function on G. In this paper, we define the Roman bondage $b_R(G)$ of a graph G with maximum degree at least two to be the minimum cardinality of all sets E' ⊆ E(G) for which $γ_R(G -E') > γ_R(G)$. We determine the Roman bondage number in several classes of graphs and give some sharp bounds.
    Źródło:
    Discussiones Mathematicae Graph Theory; 2011, 31, 4; 763-773
    2083-5892
    Pojawia się w:
    Discussiones Mathematicae Graph Theory
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    A note on the independent Roman domination in unicyclic graphs
    Autorzy:
    Chellali, M.
    Rad, N. J.
    Powiązania:
    https://bibliotekanauki.pl/articles/255989.pdf
    Data publikacji:
    2012
    Wydawca:
    Akademia Górniczo-Hutnicza im. Stanisława Staszica w Krakowie. Wydawnictwo AGH
    Tematy:
    Roman domination
    independent Roman domination
    strong equality
    Opis:
    A Roman dominating function (RDF) on a graph G= (V, E) is a function ƒ : V → {0, 1, 2} satisfying the condition that every vertex u for which ƒ(u) = 0 is adjacent to at least one vertex v for which ƒ(v)=2. The weight of an RDF is the value [formula]. An RDF ƒ in a graph G is independent if no two vertices assigned positive values are adjacent. The Roman domination number ΥR (G) (respectively, the independent Roman domination number ΥR(G) is the minimum weight of an RDF (respectively, independent RDF) on G. We say that ΥR(G) strongly equals iR(G), denoted by ΥR(G) ≡ iR(G), if every RDF on G of minimum weight is independent. In this note we characterize all unicyclic graphs G with ΥR(G) ≡ iR(G).
    Źródło:
    Opuscula Mathematica; 2012, 32, 4; 715-718
    1232-9274
    2300-6919
    Pojawia się w:
    Opuscula Mathematica
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Strong Equality Between the Roman Domination and Independent Roman Domination Numbers in Trees
    Autorzy:
    Chellali, Mustapha
    Rad, Nader Jafari
    Powiązania:
    https://bibliotekanauki.pl/articles/30146596.pdf
    Data publikacji:
    2013-05-01
    Wydawca:
    Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
    Tematy:
    Roman domination
    independent Roman domination
    strong equality
    trees
    Opis:
    A Roman dominating function (RDF) on a graph $G = (V,E)$ is a function $ f : V \rightarrow {0, 1, 2} $ satisfying the condition that every vertex $ u $ for which $ f(u) = 0 $ is adjacent to at least one vertex $v$ for which $f(v) = 2$. The weight of an RDF is the value $ f(V (G)) = \Sigma_{u \in V (G) } f(u) $. An RDF $f$ in a graph $G$ is independent if no two vertices assigned positive values are adjacent. The Roman domination number $ \gamma_R (G) $ (respectively, the independent Roman domination number $ i_R(G) $) is the minimum weight of an RDF (respectively, independent RDF) on $G$. We say that $ \gamma_R(G)$ strongly equals $ i_R(G)$, denoted by $ \gamma_R (G) \equiv i_R(G)$, if every RDF on $G$ of minimum weight is independent. In this paper we provide a constructive characterization of trees $T$ with $ \gamma_R(T) \equiv i_R(T) $.
    Źródło:
    Discussiones Mathematicae Graph Theory; 2013, 33, 2; 337-346
    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:
    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:
    A Constructive Characterization of Vertex Cover Roman Trees
    Autorzy:
    Martínez, Abel Cabrera
    Kuziak, Dorota
    Yero, Ismael G.
    Powiązania:
    https://bibliotekanauki.pl/articles/32083833.pdf
    Data publikacji:
    2021-02-01
    Wydawca:
    Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
    Tematy:
    Roman domination
    outer-independent Roman domination
    vertex cover
    vertex independence
    trees
    Opis:
    A Roman dominating function on a graph G = (V(G), E(G)) is a function f : V(G) → {0, 1, 2} satisfying the condition that every vertex u for which f(u) = 0 is adjacent to at least one vertex v for which f(v) = 2. The Roman dominating function f is an outer-independent Roman dominating function on G if the set of vertices labeled with zero under f is an independent set. The outer-independent Roman domination number γoiR(G) is the minimum weight w(f) = Σv∈V(G)f(v) of any outer-independent Roman dominating function f of G. A vertex cover of a graph G is a set of vertices that covers all the edges of G. The minimum cardinality of a vertex cover is denoted by α(G). A graph G is a vertex cover Roman graph if γoiR(G) = 2α(G). A constructive characterization of the vertex cover Roman trees is given in this article.
    Źródło:
    Discussiones Mathematicae Graph Theory; 2021, 41, 1; 267-283
    2083-5892
    Pojawia się w:
    Discussiones Mathematicae Graph Theory
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-11 z 11

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