Optimal and near-optimal mixed covering arrays by column expansion

This paper describes constructions for strength-2 mixed covering arrays developed from index-1 orthogonal arrays, ordered designs and covering arrays. The constructed arrays have optimal or near-optimal sizes. Conditions for achieving optimal size are described. An optimization among the different ingredient arrays to maximize the number of factors of each alphabet size is also presented.     

Test driving three 1995 genetic algorithms: New test functions and geometric matching

Genetic algorithms have attracted a good deal of interest in the heuristic search community. Yet there are several different types of genetic algorithms with varying performance and search characteristics. In this article we look at three genetic algorithms: an elitist simple genetic algorithm, the CHC algorithm and Genitor. One problem in comparing algorithms is that most test problems in the genetic algorithm literature can be solved using simple local search methods. In this article, the three algorithms are compared using new test problems that are not readily solved using simple local search methods. We then compare a local search method to genetic algorithms for geometric matching and examine a hybrid algorithm that combines local and genetic search. The geometric matching problem matches a model (e.g., a line drawing) to a subset of lines contained in a field of line fragments. Local search is currently the best known method for solving general geometric matching problems.     

Optimal electric power scheduling: A large nonlinear programming test problem solved by recursive quadratic programming

This paper discusses a nonlinear programming problem which arises when the optimum scheduling of an electric power system is being considered. A realistic, moderately large text example is described in detail; and the solution of this example by a recent method based on quadratic programming is also reported.     

Principal components in the nonnormal case: The test of equality of Q roots

The limiting distribution of the likelihood ratio statistic W_q for testing the hypothesis of equality of q characteristic roots of a covariance matrix is studied in the case of nonnormal populations. It is shown, both theoretically and empirically, that the limiting distribution of W_q is not robust to departures from normality and that W_q cannot be used for nonnormal populations with long tails. For the class of elliptical populations the limiting distribution of W_q can be expressed in close form. A corrected test statistic, W_q^*, is proposed that can be used in principal component analysis when sampling from elliptical populations.     

The mixed and multi model line balancing problem: a comparison

The balancing problem deals with the assignment of tasks to work stations. We can distinguish two approaches in the literature on the mixed model line balancing problem, that both transform this problem into a single model line balancing problem. These approaches use combined precedence diagrams and adjusted task processing times, respectively.An experiment was carried out to compare several heuristics based on the combined precedence diagram. A new optimisation method has been developed. The results indicate that the position of common tasks in the precedence diagram of the different models has a significant effect on both the CPU time and the unequal distribution of the total work content of single models among work stations. Moreover, good solutions with respect to the number of required stations go together with long CPU times. For several instances, we decreased the CPU times considerably without deteriorating the performance of the methods, by using a reversed combined precedence diagram.     

The minimization of open stacks problem: A review of some properties and their use in pre-processing operations

Pre-processing operations that reduce the size of a problem may be decisive for solving or not solving practical instances of a NP-hard problem. In this article we review some properties suggested in the literature for the minimization of open stacks problem that can be used in pre-processing operations to reduce the instances sizes. We also present a new pre-processing technique that may be very effective in reducing the size of an instance. We present computational tests with the suggested pre-processing operations applied on sets of MOSP instances of the literature and we show that the reductions obtained can be significant.