We are solving a tactical mail delivery problem by combining exact and heuristic methods. Routes for postpersons have to be planned visiting each customer exactly once at minimum cost. Four different modes (car, moped, bicycle, and walking) are available, but not all customers are accessible by all modes. In addition, it is possible to change the mode in the tour and walk a loop, which is calle...

A true-to-mechanism model is proposed, which considers steady-state two-phase ̄ow in porous media (SS2uPM) as a composition of two prototype ̄ows, namely ganglion dynamics (GD) and connected-oil pathway ̄ow (CPF). Coupling of the prototype ̄ows is e€ected with the simple rule that the macroscopic pressure gradient is the same in both. For a given set of values of the ̄ow system parameters, a dom...

In compilers for machines with instruction-level parallelism, the phases of register assignment and instruction scheduling can be antagonistic. Whichever phase is executed first can have negative effects on the other’s performance. This paper describes a framework, called CRAIG (Combining Register Assignment Interference Graphs), that combines register assignment and instruction scheduling to a...

A fair allocation of workload to people is crucial for securing job satisfaction. Researchers have introduced numerous objectives and algorithms to represent and improve fairness in personnel rostering problems. These approaches should not ignore the roster quality that is influenced by personnel rostering constraints, such as maximum working times, minimum rest times, etc. The present paper pr...

Given an undirected graph G and an integer k, a k-club is a subset of nodes that induces a subgraph with diameter at most k. The k-club problem consists of identifying a maximum cardinality k-club in G. It is an NP-hard problem. The problem of checking if a given k-club is maximal or if it is a subset of a larger k-club is also NP-hard, due to the non-hereditary nature of the k-club structure. ...

In this paper, we describe an aircraft loading problem submitted by the French military agency (DGA) as part of a more general military airlift planning problem. It can be viewed as a kind of bi-dimensional bin-packing problem, with heterogeneous bins and several additional constraints. We introduce two-phase methods for solving this NP-hard problem. The first phase consists in building good in...

We describe a two phase algorithm for MAX{SAT and weighted MAX{ SAT problems. In the rst phase, we use the GSAT heuristic to nd a good solution to the problem. In the second phase, we use an enumera-tion procedure based on the Davis{Putnam{Loveland algorithm, to nd a provably optimal solution. The rst heuristic stage improves the performance of the algorithm by obtaining an upper bound on the m...

In dispersed two-phase flow, experimental data indicate that the effective drag force on individual dispersed elements∗ is strongly influenced when the dispersed phase is present at high volume fractions. This appears to be true whether the DPEs are solid or fluid (i.e. droplets or bubbles). The paper first reviews the literature relating to the modelling of the drag force in densely dispersed ...

The numerical peculiarities which inhabit the numerical instance of a MOCO problem may seriously decrease the effectiveness of an approximation method. To deal with this problem we propose a flexible two-phase method for MOCO. Phase 1 produces a good approximation of the efficient frontier. However it may not be of good enough quality in terms of density. The aim of phase 2 is to tackle this pr...

This paper presents a systematic model, two-phase optimization algorithms (TPOA), for Mastermind. TPOA is not only able to efficiently obtain approximate results but also effectively discover results that are getting closer to the optima. This systematic approach could be regarded as a general improver for heuristics. That is, given a constructive heuristic, TPOA has a higher chance to obtain r...