22,567 research outputs found
On double domination in graphs
In a graph G, a vertex dominates itself and its neighbors. A subset S ⊆ V(G) is a double dominating set of G if S dominates every vertex of G at least twice. The minimum cardinality of a double dominating set of G is the double domination number γ ×2(G). A function f(p) is defined, and it is shown that γ ×2(G) = minf(p), where the minimum is taken over the n-dimensional cube Cn = {p = (p1,…,pn) | pi ∈ IR, 0 ≤ pi ≤ 1,i = 1,…,n}. Using this result, it is then shown that if G has order n with minimum degree δ and average degree d, then γ×2(G) ≤ ((ln(1+d)+lnδ+1)/δ)n
A new approach on locally checkable problems
By providing a new framework, we extend previous results on locally checkable
problems in bounded treewidth graphs. As a consequence, we show how to solve,
in polynomial time for bounded treewidth graphs, double Roman domination and
Grundy domination, among other problems for which no such algorithm was
previously known. Moreover, by proving that fixed powers of bounded degree and
bounded treewidth graphs are also bounded degree and bounded treewidth graphs,
we can enlarge the family of problems that can be solved in polynomial time for
these graph classes, including distance coloring problems and distance
domination problems (for bounded distances)
Outer Independent Double Italian Domination of Some Graph Products
An outer independent double Italian dominating function on a graph is a function for which each vertex with then and vertices assigned under are independent. The outer independent double Italian domination number is the minimum weight of an outer independent double Italian dominating function of graph . In this work, we present some contributions to the study of outer independent double Italian domination of three graph products. We characterize the Cartesian product, lexicographic product and direct product of custom graphs in terms of this parameter. We also provide the best possible upper and lower bounds for these three products for arbitrary graphs
Degree Sequence Index Strategy
We introduce a procedure, called the Degree Sequence Index Strategy (DSI), by
which to bound graph invariants by certain indices in the ordered degree
sequence. As an illustration of the DSI strategy, we show how it can be used to
give new upper and lower bounds on the -independence and the -domination
numbers. These include, among other things, a double generalization of the
annihilation number, a recently introduced upper bound on the independence
number. Next, we use the DSI strategy in conjunction with planarity, to
generalize some results of Caro and Roddity about independence number in planar
graphs. Lastly, for claw-free and -free graphs, we use DSI to
generalize some results of Faudree, Gould, Jacobson, Lesniak and Lindquester
Some Bounds on the Double Domination of Signed Generalized Petersen Graphs and Signed I-Graphs
In a graph , a vertex dominates itself and its neighbors. A subset is a double dominating set of if dominates every vertex
of at least twice. A signed graph is a graph
together with an assignment of positive or negative signs to all its
edges. A cycle in a signed graph is positive if the product of its edge signs
is positive. A signed graph is balanced if all its cycles are positive. A
subset is a double dominating set of if it
satisfies the following conditions: (i) is a double dominating set of ,
and (ii) is balanced, where
is the subgraph of induced by the edges of with one end point
in and the other end point in . The cardinality of a minimum
double dominating set of is the double domination number
. In this paper, we give bounds for the double
domination number of signed cubic graphs. We also obtain some bounds on the
double domination number of signed generalized Petersen graphs and signed
I-graphs.Comment: 13 page
Signed double Roman domination on cubic graphs
The signed double Roman domination problem is a combinatorial optimization
problem on a graph asking to assign a label from to each
vertex feasibly, such that the total sum of assigned labels is minimized. Here
feasibility is given whenever (i) vertices labeled have at least one
neighbor with label in ; (ii) each vertex labeled has one
-labeled neighbor or at least two -labeled neighbors; and (iii) the sum
of labels over the closed neighborhood of any vertex is positive. The
cumulative weight of an optimal labeling is called signed double Roman
domination number (SDRDN). In this work, we first consider the problem on
general cubic graphs of order for which we present a sharp
lower bound for the SDRDN by means of the discharging method. Moreover, we
derive a new best upper bound. Observing that we are often able to minimize the
SDRDN over the class of cubic graphs of a fixed order, we then study in this
context generalized Petersen graphs for independent interest, for which we
propose a constraint programming guided proof. We then use these insights to
determine the SDRDNs of subcubic grid graphs, among other results
The k-tuple domination number revisited
The following fundamental result for the domination number γ (G) of a graph G was proved by Alon and Spencer, Arnautov, Lovász and Payan: γ (G) ≤ frac(ln (δ + 1) + 1, δ + 1) n, where n is the order and δ is the minimum degree of vertices of G. A similar upper bound for the double domination number was found by Harant and Henning [J. Harant, M.A. Henning, On double domination in graphs, Discuss. Math. Graph Theory 25 (2005) 29-34], and for the triple domination number by Rautenbach and Volkmann [D. Rautenbach, L. Volkmann, New bounds on the k-domination number and the k-tuple domination number, Appl. Math. Lett. 20 (2007) 98-102], who also posed the interesting conjecture on the k-tuple domination number: for any graph G with δ ≥ k - 1, γ× k (G) ≤ frac(ln (δ - k + 2) + ln (over(d, ̂)k - 1 + over(d, ̂)k - 2) + 1, δ - k + 2) n, where over(d, ̂)m = ∑i = 1n ((di; m)) / n is the m-degree of G. This conjecture, if true, would generalize all the mentioned upper bounds and improve an upper bound proved in [A. Gagarin, V. Zverovich, A generalised upper bound for the k-tuple domination number, Discrete Math. (2007), in press (doi:10.1016/j.disc.2007.07.033)]. In this paper, we prove the Rautenbach-Volkmann conjecture. © 2007 Elsevier Ltd. All rights reserved
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