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1
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On graphs with a unique minimum hull set

100%
Chartrand G., Zhang P.
Discussiones Mathematicae Graph Theory
|
2001
|
tom 21
|
nr 1
31-42
EN
We show that for every integer k ≥ 2 and every k graphs G₁,G₂,...,Gₖ, there exists a hull graph with k hull vertices v₁,v₂,...,vₖ such that link $L(v_i) = G_i$ for 1 ≤ i ≤ k. Moreover, every pair a, b of integers with 2 ≤ a ≤ b is realizable as the hull number and geodetic number (or upper geodetic number) of a hull graph. We also show that every pair a,b of integers with a ≥ 2 and b ≥ 0 is realizable as the hull number and forcing geodetic number of a hull graph.
2
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The forcing geodetic number of a graph

100%
Chartrand G., Zhang P.
Discussiones Mathematicae Graph Theory
|
1999
|
tom 19
|
nr 1
45-58
EN
For two vertices u and v of a graph G, the set I(u, v) consists of all vertices lying on some u-v geodesic in G. If S is a set of vertices of G, then I(S) is the union of all sets I(u,v) for u, v ∈ S. A set S is a geodetic set if I(S) = V(G). A minimum geodetic set is a geodetic set of minimum cardinality and this cardinality is the geodetic number g(G). A subset T of a minimum geodetic set S is called a forcing subset for S if S is the unique minimum geodetic set containing T. The forcing geodetic number $f_G(S)$ of S is the minimum cardinality among the forcing subsets of S, and the forcing geodetic number f(G) of G is the minimum forcing geodetic number among all minimum geodetic sets of G. The forcing geodetic numbers of several classes of graphs are determined. For every graph G, f(G) ≤ g(G). It is shown that for all integers a, b with 0 ≤ a ≤ b, a connected graph G such that f(G) = a and g(G) = b exists if and only if (a,b) ∉ {(1,1),(2,2)}.
3
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Rotation and jump distances between graphs

81%
Chartrand G., Gavlas H., Hevia H., Johnson M.
Discussiones Mathematicae Graph Theory
|
1997
|
tom 17
|
nr 2
285-300
EN
A graph H is obtained from a graph G by an edge rotation if G contains three distinct vertices u,v, and w such that uv ∈ E(G), uw ∉ E(G), and H = G-uv+uw. A graph H is obtained from a graph G by an edge jump if G contains four distinct vertices u,v,w, and x such that uv ∈ E(G), wx∉ E(G), and H = G-uv+wx. If a graph H is obtained from a graph G by a sequence of edge jumps, then G is said to be j-transformed into H. It is shown that for every two graphs G and H of the same order (at least 5) and same size, G can be j-transformed into H. For every two graphs G and H of the same order and same size, the jump distance $d_j(G,H)$ between G and H is defined as the minimum number of edge jumps required to j-transform G into H. The rotation distance $d_r(G,H)$ between two graphs G and H of the same order and same size is the minimum number of edge rotations needed to transform G into H. The jump and rotation distances of two graphs of the same order and same size are compared. For a set S of graphs of a fixed order at least 5 and fixed size, the jump distance graph $D_j(S)$ of S has S as its vertex set and where G₁ and G₂ in S are adjacent if and only if $d_j(G₁,G₂) = 1$. A graph G is a jump distance graph if there exists a set S of graphs of the same order and same size with $D_j(S) = G$. Several graphs are shown to be jump distance graphs, including all complete graphs, trees, cycles, and cartesian products of jump distance graphs.
4
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Geodetic sets in graphs

81%
Chartrand G., Harary F., Zhang P.
Discussiones Mathematicae Graph Theory
|
2000
|
tom 20
|
nr 1
129-138
EN
For two vertices u and v of a graph G, the closed interval I[u,v] consists of u, v, and all vertices lying in some u-v geodesic in G. If S is a set of vertices of G, then I[S] is the union of all sets I[u,v] for u, v ∈ S. If I[S] = V(G), then S is a geodetic set for G. The geodetic number g(G) is the minimum cardinality of a geodetic set. A set S of vertices in a graph G is uniform if the distance between every two distinct vertices of S is the same fixed number. A geodetic set is essential if for every two distinct vertices u,v ∈ S, there exists a third vertex w of G that lies in some u-v geodesic but in no x-y geodesic for x, y ∈ S and {x,y} ≠ {u,v}. It is shown that for every integer k ≥ 2, there exists a connected graph G with g(G) = k which contains a uniform, essential minimum geodetic set. A minimal geodetic set S has no proper subset which is a geodetic set. The maximum cardinality of a minimal geodetic set is the upper geodetic number g⁺(G). It is shown that every two integers a and b with 2 ≤ a ≤ b are realizable as the geodetic and upper geodetic numbers, respectively, of some graph and when a < b the minimum order of such a graph is b+2.
5
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Full domination in graphs

81%
Brigham R., Chartrand G., Dutton R., Zhang P.
Discussiones Mathematicae Graph Theory
|
2001
|
tom 21
|
nr 1
43-62
EN
For each vertex v in a graph G, let there be associated a subgraph $H_v$ of G. The vertex v is said to dominate $H_v$ as well as dominate each vertex and edge of $H_v$. A set S of vertices of G is called a full dominating set if every vertex of G is dominated by some vertex of S, as is every edge of G. The minimum cardinality of a full dominating set of G is its full domination number $γ_{FH}(G)$. A full dominating set of G of cardinality $γ_{FH}(G)$ is called a $γ_{FH}$-set of G. We study three types of full domination in graphs: full star domination, where $H_v$ is the maximum star centered at v, full closed domination, where $H_v$ is the subgraph induced by the closed neighborhood of v, and full open domination, where $H_v$ is the subgraph induced by the open neighborhood of v.
6
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Radio k-colorings of paths

81%
Chartrand G., Nebeský L., Zhang P.
Discussiones Mathematicae Graph Theory
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2004
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tom 24
|
nr 1
5-21
EN
For a connected graph G of diameter d and an integer k with 1 ≤ k ≤ d, a radio k-coloring of G is an assignment c of colors (positive integers) to the vertices of G such that d(u,v) + |c(u)- c(v)| ≥ 1 + k for every two distinct vertices u and v of G, where d(u,v) is the distance between u and v. The value rcₖ(c) of a radio k-coloring c of G is the maximum color assigned to a vertex of G. The radio k-chromatic number rcₖ(G) of G is the minimum value of rcₖ(c) taken over all radio k-colorings c of G. In this paper, radio k-colorings of paths are studied. For the path Pₙ of order n ≥ 9 and n odd, a new improved bound for $rc_{n- 2}(Pₙ)$ is presented. For n ≥ 4, it is shown that $rc_{n-3}(Pₙ) ≤ \binom{n-2} {2}$ Upper and lower bounds are also presented for rcₖ(Pₙ) in terms of k when 1 ≤ k ≤ n- 1. The upper bound is shown to be sharp when 1 ≤ k ≤ 4 and n is sufficiently large.
7
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Kaleidoscopic Colorings of Graphs

81%
Chartrand G., English S., Zhang P.
Discussiones Mathematicae Graph Theory
|
2017
|
tom 37
|
nr 3
711-727
EN
For an r-regular graph G, let c : E(G) → [k] = {1, 2, . . . , k}, k ≥ 3, be an edge coloring of G, where every vertex of G is incident with at least one edge of each color. For a vertex v of G, the multiset-color cm(v) of v is defined as the ordered k-tuple (a1, a2, . . . , ak) or a1a2 … ak, where ai (1 ≤ i ≤ k) is the number of edges in G colored i that are incident with v. The edge coloring c is called k-kaleidoscopic if cm(u) ≠ cm(v) for every two distinct vertices u and v of G. A regular graph G is called a k-kaleidoscope if G has a k-kaleidoscopic coloring. It is shown that for each integer k ≥ 3, the complete graph Kk+3 is a k-kaleidoscope and the complete graph Kn is a 3-kaleidoscope for each integer n ≥ 6. The largest order of an r-regular 3-kaleidoscope is [...] (r−12) $\left( {\matrix{{r - 1} \cr 2 } } \right)$ . It is shown that for each integer r ≥ 5 such that r ≢ 3 (mod 4), there exists an r-regular 3-kaleidoscope of order [...] (r−12) $\left( {{{r - 1} \over 2}} \right)$ .
8
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A sufficient condition for graphs with 1-factors

81%
Chartrand G., Goldsmith D. L., Schuster S.
Colloquium Mathematicum
|
1979
|
tom 41
|
nr 2
339-344
9
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Distance defined by spanning trees in graphs

81%
Chartrand G., Nebeský L., Zhang P.
Discussiones Mathematicae Graph Theory
|
2007
|
tom 27
|
nr 3
485-506
EN
For a spanning tree T in a nontrivial connected graph G and for vertices u and v in G, there exists a unique u-v path u = u₀, u₁, u₂,..., uₖ = v in T. A u-v T-path in G is a u- v path u = v₀, v₁,...,vₗ = v in G that is a subsequence of the sequence u = u₀, u₁, u₂,..., uₖ = v. A u-v T-path of minimum length is a u-v T-geodesic in G. The T-distance $d_{G|T}(u,v)$ from u to v in G is the length of a u-v T-geodesic. Let geo(G) and geo(G|T) be the set of geodesics and the set of T-geodesics respectively in G. Necessary and sufficient conditions are established for (1) geo(G) = geo(G|T) and (2) geo(G|T) = geo(G|T*), where T and T* are two spanning trees of G. It is shown for a connected graph G that geo(G|T) = geo(G) for every spanning tree T of G if and only if G is a block graph. For a spanning tree T of a connected graph G, it is also shown that geo(G|T) satisfies seven of the eight axioms of the characterization of geo(G). Furthermore, we study the relationship between the distance d and T-distance $d_{G|T}$ in graphs and present several realization results on parameters and subgraphs defined by these two distances.
10
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Recognizable colorings of graphs

81%
Chartrand G., Lesniak L., VanderJagt D., Zhang P.
Discussiones Mathematicae Graph Theory
|
2008
|
tom 28
|
nr 1
35-57
EN
Let G be a connected graph and let c:V(G) → {1,2,...,k} be a coloring of the vertices of G for some positive integer k (where adjacent vertices may be colored the same). The color code of a vertex v of G (with respect to c) is the ordered (k+1)-tuple code(v) = (a₀,a₁,...,aₖ) where a₀ is the color assigned to v and for 1 ≤ i ≤ k, $a_i$ is the number of vertices adjacent to v that are colored i. The coloring c is called recognizable if distinct vertices have distinct color codes and the recognition number rn(G) of G is the minimum positive integer k for which G has a recognizable k-coloring. Recognition numbers of complete multipartite graphs are determined and characterizations of connected graphs of order n having recognition numbers n or n-1 are established. It is shown that for each pair k,n of integers with 2 ≤ k ≤ n, there exists a connected graph of order n having recognition number k. Recognition numbers of cycles, paths, and trees are investigated.
11
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On γ-labelings of trees

81%
Chartrand G., Erwin D., VanderJagt D., Zhang P.
Discussiones Mathematicae Graph Theory
|
2005
|
tom 25
|
nr 3
363-383
EN
Let G be a graph of order n and size m. A γ-labeling of G is a one-to-one function f:V(G) → {0,1,2,...,m} that induces a labeling f': E(G) → {1,2,...,m} of the edges of G defined by f'(e) = |f(u)-f(v)| for each edge e = uv of G. The value of a γ-labeling f is $val(f) = Σ_{e ∈ E(G)}f'K(e)$. The maximum value of a γ-labeling of G is defined as $val_{max}(G) = max {val(f) : f is a γ- labeling of G}$; while the minimum value of a γ-labeling of G is $val_{min}(G) = min {val(f) : f is a γ- labeling of G}$; The values $val_{max}(S_{p,q})$ and $val_{min}(S_{p,q})$ are determined for double stars $S_{p,q}$. We present characterizations of connected graphs G of order n for which $val_{min}(G) = n$ or $val_{min}(G) = n+1$.
12
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The set chromatic number of a graph

81%
Chartrand G., Okamoto F., Rasmussen C., Zhang P.
Discussiones Mathematicae Graph Theory
|
2009
|
tom 29
|
nr 3
545-561
EN
For a nontrivial connected graph G, let c: V(G)→ N be a vertex coloring of G where adjacent vertices may be colored the same. For a vertex v of G, the neighborhood color set NC(v) is the set of colors of the neighbors of v. The coloring c is called a set coloring if NC(u) ≠ NC(v) for every pair u,v of adjacent vertices of G. The minimum number of colors required of such a coloring is called the set chromatic number χₛ(G) of G. The set chromatic numbers of some well-known classes of graphs are determined and several bounds are established for the set chromatic number of a graph in terms of other graphical parameters.
13
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A technique for reconstructing disconnected graphs

80%
Chartrand G., Kronk H. V., Schuster S.
Colloquium Mathematicum
|
1973
|
tom 27
|
nr 1
31-34
14
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On minimal regular digraphs with given girth

80%
Behzad M., Chartrand G., Wall C. E.
Fundamenta Mathematicae
|
1970
|
tom 69
|
nr 3
227-231
15
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On Hamiltonian properties of powers of special Hamiltonian graphs

80%
Chartrand G., Kapoor S. F.
Colloquium Mathematicum
|
1974
|
tom 29
|
nr 1
113-117
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