منابع مشابه
Positive graphs
We study “positive” graphs that have a nonnegative homomorphism number into every edge-weighted graph (where the edgeweights may be negative). We conjecture that all positive graphs can be obtained by taking two copies of an arbitrary simple graph and gluing them together along an independent set of nodes. We prove the conjecture for various classes of graphs including all trees. We prove a num...
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(V,E) be a finite undirected graph with vertex set V and edge set E. A mapping f ~ {O.l}m is called an M-coding of G, if the induced mapping g : V ~ {O,l • defined as g(v) f(uv). assigns ueV,uveE different vectors to the vertices of G, where all summations are mod 2.An M-coding f is calle~ positive if the zero vector is not assigned to any edge and the induced labelling g does not assign the ze...
متن کاملProperties of θ-super positive graphs
Let the matching polynomial of a graph G be denoted by μ(G, x). A graph G is said to be θ-super positive if μ(G, θ) 6= 0 and μ(G \ v, θ) = 0 for all v ∈ V (G). In particular, G is 0-super positive if and only if G has a perfect matching. While much is known about 0-super positive graphs, almost nothing is known about θsuper positive graphs for θ 6= 0. This motivates us to investigate the struct...
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In this paper we construct inverse bijections between two sequences of finite sets. One sequence is defined by planar diagrams and the other by lattice walks. In [10] it is shown that the number of elements in these two sets are equal. This problem and the methods we use are motivated by the representation theory of the exceptional simple Lie algebra G2. However in this account we have emphasis...
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ژورنال
عنوان ژورنال: European Journal of Combinatorics
سال: 2016
ISSN: 0195-6698
DOI: 10.1016/j.ejc.2015.07.007