A greedy heuristic to solve a given combinatorial optimisation problem can be seen as an element of an infinite set of heuristics, H, which is defined by a function that depends on several parameters. We propose a procedure for determining the best element of H for a set of instances of the combinatorial optimisation problem. The procedure consists essentially in applying a direct non-linear op...

The present contribution deals with the numerical modeling of railway track-supporting systems-using coupled finite-infinite elements-to represent the near and distant field stress distribution, and also employing a thin layer interface element to account for the interfacial behavior between sleepers and ballast. To simulate the relative debonding, slipping and crushing at the contact area betw...

For an element x of a ring R, let A (x), Ar(x), and A(x) denote, respectively, the left, right and two-sided annihilator of x in R. For a set X , we denote cardX by |X|; and say that a subset Y of X is large in X if |Y | = |X|. We prove that if x is any nilpotent element and I is any infinite ideal of R, then A(x) ∩ I is large in I , and in particular |A (x)| = |Ar(x)| = |A(x)| = |R|. The last ...

A tournament is acyclically indecomposable if no acyclic autonomous set of vertices has more than one element. We identify twelve infinite acyclically indecomposable tournaments and prove that every infinite acyclically indecomposable tournament contains a subtournament isomorphic to one of these tournaments. The profile of a tournament T is the function φT which counts for each integer n the n...