An algebraic and combinatorial approach to the study ofthe Quadratic Assignment Problem produced theoretical results that canbe applied to (meta) heuristics to give them information about theproblem structure, allowing the construction of algorithms. In thispaper those results were applied to inform a Simulated Annealing-typeheuristic (which we called RedInv-SA). Some results from tests withknown literature instances are presented.

The standard multiple criteria optimization starts with anassumption that the criteria are incomparable. However, there are manyapplications in which the criteria express ideas of allocation ofresources meant to achieve some equitable distribution. This paperfocuses on solving linear multiple criteria optimization problems withuniform criteria treated in an equitable way. An axiomatic definition ofequitable efficiency is introduced as an refinement ofPareto-optimality. Various generation techniques are examined and thestructure of the equitably efficient set is analyzed.

In this paper, a discrete-event simulation model iscoupled with a genetic algorithm to treat highly combinatorialscheduling problems encountered in a production campaign of a finechemistry plant. The main constraints and features of fine chemistryhave been taken into account in the development of the model, thusallowing a realistic evaluation of the objective function used in thestochastic optimization procedure. After a presentation of problemcombinatorics, the coupling strategy is then proposed and illustrated byan example of industrial size (24 equipment items, 140 products, 12different production recipes and 40 products to be recycled during thecampaign). This example serves as an incentive to show how the approachcan improve production performance. Three technical criteria have beenstudied: campaign completion time, average product cycle time, respectof due-dates. Two kinds of optimization variables have been considered:product input order and/or allocation of heuristics for conflittreatment. The results obtained are then analysed and some perspectivesof this work are presented.

Comparing q-ary relations on a set ${\cal O}$ ofelementary objects is one of the most fundamental problems ofclassification and combinatorial data analysis. In this paper thespecific comparison task that involvesclassification tree structures (binary or not) is considered in thiscontext. Two mathematical representationsare proposed. One is defined in terms of a weighted binary relation; the second uses a 4-ary relation.The most classical approaches to tree comparison are discussed in thecontext of a set theoretic representation of these relations. Formalandcombinatorial computing aspects of a construction method for a verygeneralfamily of association coefficients between relations are presented. The main purpose of this article is to specify the componentsof this construction, based on a permutational procedure, when thestructuresto be compared are classification trees.

We show that the problem of deciding if there is a scheduleof length three for the multiprocessor scheduling problem on identicalmachines and unit execution time tasks in -complete even for bipartitegraphs, i.e. for precedence graphs of depth one. This complexity resultextends a classical result of Lenstra and Rinnoy Kan [5].

Single server queues with repeated attempts are useful inthe modeling of computer and telecommunication systems. In addition, weconsider in this paper the possibility of disasters. When a disasteroccurs, all the customers present in the system are destroyedimmediately. Using a regenerative approach, we derive a numericallystable recursion scheme for the state probabilities. This model can beemployed to analyze the behaviour of a buffer in computers with virusinfections.