Search results for "Discrete Mathematics and Combinatorics"

Additivity of affine designs

2020

We show that any affine block design $$\mathcal{D}=(\mathcal{P},\mathcal{B})$$ is a subset of a suitable commutative group $${\mathfrak {G}}_\mathcal{D},$$ with the property that a k-subset of $$\mathcal{P}$$ is a block of $$\mathcal{D}$$ if and only if its k elements sum up to zero. As a consequence, the group of automorphisms of any affine design $$\mathcal{D}$$ is the group of automorphisms of $${\mathfrak {G}}_\mathcal{D}$$ that leave $$\mathcal P$$ invariant. Whenever k is a prime p,  $${\mathfrak {G}}_\mathcal{D}$$ is an elementary abelian p-group.

Linear and cyclic radio k-labelings of trees

2007

International audience; Motivated by problems in radio channel assignments, we consider radio k-labelings of graphs. For a connected graph G and an integer k ≥ 1, a linear radio k-labeling of G is an assignment f of nonnegative integers to the vertices of G such that |f(x)−f(y)| ≥ k+1−dG(x,y), for any two distinct vertices x and y, where dG(x,y) is the distance between x and y in G. A cyclic k-labeling of G is defined analogously by using the cyclic metric on the labels. In both cases, we are interested in minimizing the span of the labeling. The linear (cyclic, respectively) radio k-labeling number of G is the minimum span of a linear (cyclic, respectively) radio k-labeling of G. In this p…

Preface

2018

This issue of Discrete and Continuous Dynamical Systems-Series S focuses on the qualitative analysis of some concrete nonlinear problems, e.g., ordinary, partial differential equations, systems and inclusions. The ten contributions collected here give an overview on some very recent results on the existence, multiplicity and sign information of the solutions of a wide range of nonlinear differential problems involving different boundary value conditions and operators in divergence form. In our opinion, the synergy pointed out here between the classical nonlinear analysis methods, like the critical point theory, sub-super solutions methods, truncation and comparison techniques, Morse theory,…

Melnikov functions and Bautin ideal

2001

The computation of the number of limit cycles which appear in an analytic unfolding of planar vector fields is related to the decomposition of the displacement function of this unfolding in an ideal of functions in the parameter space, called the Ideal of Bautin. On the other hand, the asymptotic of the displacement function, for 1-parameter unfoldings of hamiltonian vector fields is given by Melnikov functions which are defined as the coefficients of Taylor expansion in the parameter. It is interesting to compare these two notions and to study if the general estimations of the number of limit cycles in terms of the Bautin ideal could be reduced to the computations of Melnikov functions for…

On the steady state problem of the chemotaxis-consumption model with logistic growth and Dirichlet boundary condition for signal

2023

This paper concerns the steady state problem for chemotaxis consumption system with logistic growth and constant concentration of chemoat-tractant on the boundary of the domain. We establish the existence of a non-constant positive solution to this problem. The uniqueness of this solution is obtained under the smallness assumption on the boundary data. Some qualitative properties of the solutions and numerical results are presented.

Heuristics and meta-heuristics for 2-layer straight line crossing minimization

2003

AbstractThis paper presents extensive computational experiments to compare 12 heuristics and 2 meta-heuristics for the problem of minimizing straight-line crossings in a 2-layer graph. These experiments show that the performance of the heuristics (largely based on simple ordering rules) drastically deteriorates as the graphs become sparser. A tabu search metaheuristic yields the best results for relatively dense graphs, with a GRASP implementation as close second. Furthermore, the GRASP approach outperforms all other approaches when tackling low-density graphs.

Coincidence problems for generalized contractions

2014

In this paper, we establish some new existence, uniqueness and Ulam-Hyers stability theorems for coincidence problems for two single-valued mappings. The main results of this paper extend the results presented in O. Mle?ni?e: Existence and Ulam-Hyers stability results for coincidence problems, J. Non-linear Sci. Appl., 6(2013), 108-116. In the last section two examples of application of these results are also given.

A Sokoban-type game and arc deletion within irregular digraphs of all sizes

2007

Time-dependent asymmetric traveling salesman problem with time windows: Properties and an exact algorithm

2019

Abstract In this paper, we deal with the Time-Dependent Asymmetric Traveling Salesman Problem with Time Windows. First, we prove that under special conditions the problem can be solved as an Asymmetric Traveling Salesman Problem with Time Windows, with suitable-defined time windows and (constant) travel times. Second, we show that, if the special conditions do not hold, the time-independent optimal solution provides both a lower bound and (eventually) an upper bound with a worst-case guarantee for the Time-Dependent Asymmetric Traveling Salesman Problem with Time Windows. Finally, a branch-and-bound algorithm is presented and tested on a set of 4800 instances. The results have been compared…

Neighbor-Distinguishing k-tuple Edge-Colorings of Graphs

2009

AbstractThis paper studies proper k-tuple edge-colorings of graphs that distinguish neighboring vertices by their sets of colors. Minimum numbers of colors for such colorings are determined for cycles, complete graphs and complete bipartite graphs. A variation in which the color sets assigned to edges have to form cyclic intervals is also studied and similar results are given.