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تسجيل مستخدم جديدA note on total co-independent domination in trees
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A set $D$ of vertices of a graph $G$ is a total dominating set if every vertex of $G$ is adjacent to at least one vertex of $D$. The total domination number of $G$ is the minimum cardinality of any total dominating set of $G$ and is denoted by $gamma_t(G)$. The total dominating set $D$ is called a total co-independent dominating set if $V(G)setminus D$ is an independent set and has at least one vertex. The minimum cardinality of any total co-independent dominating set is denoted by $gamma_{t,coi}(G)$. In this paper, we show that, for any tree $T$ of order $n$ and diameter at least three, $n-beta(T)leq gamma_{t,coi}(T)leq n-|L(T)|$ where $beta(T)$ is the maximum cardinality of any independent set and $L(T)$ is the set of leaves of $T$. We also characterize the families of trees attaining the extremal bounds above and show that the differences between the value of $gamma_{t,coi}(T)$ and these bounds can be arbitrarily large for some classes of trees.
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For a graph $G=(V,E)$, we call a subset $ Ssubseteq V cup E$ a total mixed dominating set of $G$ if each element of $V cup E$ is either adjacent or incident to an element of $S$, and the total mixed domination number $gamma_{tm}(G)$ of $G$ is the min
imum cardinality of a total mixed dominating set of $G$. In this paper, we initiate to study the total mixed domination number of a connected graph by giving some tight bounds in terms of some parameters such as order and total domination numbers of the graph and its line graph. Then we discuss on the relation between total mixed domination number of a graph and its diameter. Studing of this number in trees is our next work. Also we show that the total mixed domination number of a graph is equale to the total domination number of a graph which is obtained by the graph. Giving the total mixed domination numbers of some special graphs is our last work.
Given a graph $G$, a dominating set of $G$ is a set $S$ of vertices such that each vertex not in $S$ has a neighbor in $S$. The domination number of $G$, denoted $gamma(G)$, is the minimum size of a dominating set of $G$. The independent domination n
umber of $G$, denoted $i(G)$, is the minimum size of a dominating set of $G$ that is also independent. Note that every graph has an independent dominating set, as a maximal independent set is equivalent to an independent dominating set. Let $G$ be a connected $k$-regular graph that is not $K_{k, k}$ where $kgeq 4$. Generalizing a result by Lam, Shiu, and Sun, we prove that $i(G)le frac{k-1}{2k-1}|V(G)|$, which is tight for $k = 4$. This answers a question by Goddard et al. in the affirmative. We also show that $frac{i(G)}{gamma(G)} le frac{k^3-3k^2+2}{2k^2-6k+2}$, strengthening upon a result of Knor, v{S}krekovski, and Tepeh. In addition, we prove that a graph $G$ with maximum degree at most $4$ satisfies $i(G) le frac{5}{9}|V(G)|$, which is also tight.
Let $ G $ be a graph. A subset $S subseteq V(G) $ is called a total dominating set if every vertex of $G$ is adjacent to at least one vertex of $S$. The total domination number, $gamma_{t}$($G$), is the minimum cardinality of a total dominating set o
f $G$. In this paper using a greedy algorithm we provide an upper bound for $gamma_{t}$($G$), whenever $G$ is a bipartite graph and $delta(G)$ $geq$ $k$. More precisely, we show that if $k$ > 1 is a natural number, then for every bipartite graph $G$ of order $n$ and $delta(G) ge k$, $ $$gamma_{t}$($G$) $leq$ $n(1- frac{k!}{prod_{i=0}^{k-1}(frac{k}{k-1}+i)}).$
Let $G=(V(G), E(G))$ be a multigraph with maximum degree $Delta(G)$, chromatic index $chi(G)$ and total chromatic number $chi(G)$. The Total Coloring conjecture proposed by Behzad and Vizing, independently, states that $chi(G)leq Delta(G)+mu(G) +1$ f
or a multigraph $G$, where $mu(G)$ is the multiplicity of $G$. Moreover, Goldberg conjectured that $chi(G)=chi(G)$ if $chi(G)geq Delta(G)+3$ and noticed the conjecture holds when $G$ is an edge-chromatic critical graph. By assuming the Goldberg-Seymour conjecture, we show that $chi(G)=chi(G)$ if $chi(G)geq max{ Delta(G)+2, |V(G)|+1}$ in this note. Consequently, $chi(G) = chi(G)$ if $chi(G) ge Delta(G) +2$ and $G$ has a spanning edge-chromatic critical subgraph.
A $k$-tuple total dominating set ($k$TDS) of a graph $G$ is a set $S$ of vertices in which every vertex in $G$ is adjacent to at least $k$ vertices in $S$. The minimum size of a $k$TDS is called the $k$-tuple total dominating number and it is denoted
by $gamma_{times k,t}(G)$. We give a constructive proof of a general formula for $gamma_{times 3, t}(K_n Box K_m)$.
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