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Wyświetlanie 1-3 z 3
Tytuł:
Minimal forbidden subgraphs of reducible graph properties
Autorzy:
Berger, Amelie
Powiązania:
https://bibliotekanauki.pl/articles/743439.pdf
Data publikacji:
2001
Wydawca:
Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
Tematy:
reducible graph properties
forbidden subgraphs
induced subgraphs
Opis:
A property of graphs is any class of graphs closed under isomorphism. Let ₁,₂,...,ₙ be properties of graphs. A graph G is (₁,₂,...,ₙ)-partitionable if the vertex set V(G) can be partitioned into n sets, {V₁,V₂,..., Vₙ}, such that for each i = 1,2,...,n, the graph $G[V_i] ∈ _i$. We write ₁∘₂∘...∘ₙ for the property of all graphs which have a (₁,₂,...,ₙ)-partition. An additive induced-hereditary property is called reducible if there exist additive induced-hereditary properties ₁ and ₂ such that = ₁∘₂. Otherwise is called irreducible. An additive induced-hereditary property can be defined by its minimal forbidden induced subgraphs: those graphs which are not in but which satisfy that every proper induced subgraph is in . We show that every reducible additive induced-hereditary property has infinitely many minimal forbidden induced subgraphs. This result is also seen to be true for reducible additive hereditary properties.
Źródło:
Discussiones Mathematicae Graph Theory; 2001, 21, 1; 111-117
2083-5892
Pojawia się w:
Discussiones Mathematicae Graph Theory
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Chromatic Sums for Colorings Avoiding Monochromatic Subgraphs
Autorzy:
Kubicka, Ewa
Kubicki, Grzegorz
McKeon, Kathleen A.
Powiązania:
https://bibliotekanauki.pl/articles/31339334.pdf
Data publikacji:
2015-08-01
Wydawca:
Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
Tematy:
coloring
sum of colors
forbidden subgraphs
Opis:
Given graphs G and H, a vertex coloring c : V (G) →ℕ is an H-free coloring of G if no color class contains a subgraph isomorphic to H. The H-free chromatic number of G, χ (H,G), is the minimum number of colors in an H-free coloring of G. The H-free chromatic sum of G, ∑(H,G), is the minimum value achieved by summing the vertex colors of each H-free coloring of G. We provide a general bound for ∑(H,G), discuss the computational complexity of finding this parameter for different choices of H, and prove an exact formulas for some graphs G. For every integer k and for every graph H, we construct families of graphs, Gk with the property that k more colors than χ (H,G) are required to realize ∑(H,G) for H-free colorings. More complexity results and constructions of graphs requiring extra colors are given for planar and outerplanar graphs.
Źródło:
Discussiones Mathematicae Graph Theory; 2015, 35, 3; 541-555
2083-5892
Pojawia się w:
Discussiones Mathematicae Graph Theory
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
\( \mathcal{P} \)-Apex Graphs
Autorzy:
Borowiecki, Mieczysław
Drgas-Burchardt, Ewa
Sidorowicz, Elżbieta
Powiązania:
https://bibliotekanauki.pl/articles/31342421.pdf
Data publikacji:
2018-05-01
Wydawca:
Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
Tematy:
induced hereditary classes of graphs
forbidden subgraphs
hypergraphs
transversal number
Opis:
Let \( \mathcal{P} \) be an arbitrary class of graphs that is closed under taking induced subgraphs and let \( \mathcal{C}( \mathcal{P} ) \) be the family of forbidden subgraphs for \( \mathcal{P} \). We investigate the class \( \mathcal{P} (k) \) consisting of all the graphs \( G \) for which the removal of no more than \( k \) vertices results in graphs that belong to \( \mathcal{P} \). This approach provides an analogy to apex graphs and apex-outerplanar graphs studied previously. We give a sharp upper bound on the number of vertices of graphs in \( \mathcal{C}( \mathcal{P}(1)) \) and we give a construction of graphs in \( \mathcal{C}( \mathcal{P}(k)) \) of relatively large order for \( k \ge 2 \). This construction implies a lower bound on the maximum order of graphs in \( \mathcal{C}( \mathcal{P}(k)) \). Especially, we investigate \( \mathcal{C}( \mathcal{W}_r(1)) \), where \( \mathcal{W}_r \) denotes the class of \( \mathcal{P}_r \)-free graphs. We determine some forbidden subgraphs for the class \( \mathcal{W}_r(1) \) with the minimum and maximum number of vertices. Moreover, we give sufficient conditions for graphs belonging to \( \mathcal{C} ( \mathcal{P} (k)) \), where \( \mathcal{P} \) is an additive class, and a characterisation of all forests in \( \mathcal{C} ( \mathcal{P} (k)) \). Particularly we deal with \( \mathcal{C} ( \mathcal{P} (1)) \), where \( \mathcal{P} \) is a class closed under substitution and obtain a characterisation of all graphs in the corresponding \( \mathcal{C} ( \mathcal{P} (1)) \). In order to obtain desired results we exploit some hypergraph tools and this technique gives a new result in the hypergraph theory.
Źródło:
Discussiones Mathematicae Graph Theory; 2018, 38, 2; 323-349
2083-5892
Pojawia się w:
Discussiones Mathematicae Graph Theory
Dostawca treści:
Biblioteka Nauki
Artykuł
    Wyświetlanie 1-3 z 3

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