Results 101 to 110 of about 8,697 (224)

Species on Digraphs

Advances in Mathematics, 1996
The author applies the language of Joyal's species to enumeration problems of digraphs using the machinery of coloured species, see, e.g., the author and \textit{O. Nava} [J. Comb. Theory, Ser. A 64, No. 1, 102-129 (1993; Zbl 0787.05095)]. A species over digraphs is defined as a functor from the category of digraphs to the category of finite sets and ...
openaire   +2 more sources

A Min–Max Relation on Dicuts and Dijoins in Weighted Chordal Digraphs

Journal of Graph Theory, Volume 113, Issue 3, Page 462-469, November 2026.
ABSTRACT In a digraph, a dicut is a cut where all the arcs cross in one direction. A dijoin is a subset of arcs that intersects every dicut. Edmonds and Giles conjectured that in a weighted digraph, the minimum weight of a dicut is equal to the maximum size of a packing of dijoins. This has been disproved. However, the unweighted version conjectured by
Gérard Cornuéjols, Siyue Liu, R. Ravi
wiley   +1 more source

KONSTRUKSI DIGRAPH EKSENTRIS DENGAN MATRIKS ADJACENCY [PDF]

, 2004
The objective of this thesis is to find the connection between adjacency matrix of digraph and adjacency matrix of its eccentric dib'T3ph, and algorithm for constructing eccentric digraph from digraph based on the connection.
AGUS YASIN KURNIAWAN, 089911925
core   +1 more source

On polynomial digraphs

Discrete Mathematics, 2006
Let $Φ(x,y)$ be a bivariate polynomial with complex coefficients. The zeroes of $Φ(x,y)$ are given a combinatorial structure by considering them as arcs of a directed graph $G(Φ)$. This paper studies some relationship between the polynomial $Φ(x,y)$ and the structure of $G(Φ)$.
Josep M. Brunat, Antonio Montes
openaire   +2 more sources

On the Hardness of Switching to a Small Number of Edges

Journal of Graph Theory, Volume 113, Issue 2, Page 237-251, October 2026.
ABSTRACT Seidel's switching is a graph operation which makes a given vertex adjacent to precisely those vertices to which it was non‐adjacent before, while keeping the rest of the graph unchanged. Two graphs are called switching‐equivalent if one can be made isomorphic to the other one by a sequence of switches. Jelínková et al. [DMTCS 13, no. 2, 2011]
Vít Jelínek, Eva Jelínková, Jan Kratochvíl   +2 more
wiley   +1 more source

Minimal positive realizations of linear continuous-time fractional descriptor systems: Two cases of an input-output digraph structure

International Journal of Applied Mathematics and Computer Science, 2018
In the last two decades, fractional calculus has become a subject of great interest in various areas of physics, biology, economics and other sciences. The idea of such a generalization was mentioned by Leibniz and L’Hospital.
Markowski Konrad Andrzej
doaj   +1 more source

Halin's Grid Theorem for Digraphs

Journal of Graph Theory, Volume 113, Issue 1, Page 97-112, September 2026.
ABSTRACT Halin showed that every thick end of every graph contains an infinite grid. We extend Halin's theorem to digraphs. More precisely, we show that for every infinite family ℛ of disjoint equivalent out‐rays there is a grid whose vertical rays are contained in ℛ Florian Reich
wiley   +1 more source

On Tight Tree‐Complete Hypergraph Ramsey Numbers

Journal of Graph Theory, Volume 113, Issue 1, Page 88-96, September 2026.
ABSTRACT Chvátal showed that for any tree T with k edges, the Ramsey number R ( T , n ) = k ( n − 1 ) + 1. For r = 3 or 4, we show that, if T is an r‐uniform nontrivial tight tree, then the hypergraph Ramsey number R ( T , n ) = Θ ( n r − 1 ). The 3‐uniform result comes from observing a construction of Cooper and Mubayi.
Jiaxi Nie
wiley   +1 more source

Orientations of Graphs With at Most One Directed Path Between Every Pair of Vertices

Journal of Graph Theory, Volume 113, Issue 1, Page 143-164, September 2026.
ABSTRACT Given a graph G, we say that an orientation D of G is a KT orientation if, for all u , v ∈ V ( D ), there is at most one directed path (in any direction) between u and v. Graphs that admit such orientations have been used to construct graphs with large chromatic number and small clique number that served as counterexamples to various ...
Barbora Dohnalová, Jiří Kalvoda, Gaurav Kucheriya, Sophie Spirkl   +3 more
wiley   +1 more source

The superposition method for the reconstruction of food webs

Methods in Ecology and Evolution, Volume 17, Issue 9, Page 2770-2782, September 2026.
Abstract Understanding trophic positions is essential for analysing complex food webs. While calculating these positions can be straightforward when feeding relationships and their proportions are known, determining diet coefficients traditionally requires substantial time and effort.
Ettore Barbieri, Naoto F. Ishikawa
wiley   +1 more source