Combinatorial Optimization for Constructing Covering Arrays and Sequence Covering Arrays

A special issue of Mathematics (ISSN 2227-7390). This special issue belongs to the section "Mathematics and Computer Science".

Deadline for manuscript submissions: 31 August 2024 | Viewed by 560

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UNIDAD TAMAULIPAS, CINVESTAV-Tamaulipas, Tamaulipas, Ciudad Victoria 87130, Mexico
Interests: combinatorial optimization; databases; covering arrays

Special Issue Information

Dear Colleagues,

Nowadays, many combinatorial designs have been used that have succeeded in reducing the number of trials needed to obtain certain expected results in many fields, like Software Testing Processes, Business Processes, and Industrial Processes. In general, it is highly desirable to reduce the number of trials while increasing the possibilities of obtaining certain adjustments of a configuration for a system. For instance, in Software Testing Processes, it is advantageous to use the minimum number of tests to exercise at least once: a) all combinations of values from all subsets of a certain size with the total number of input variables of a software component; and b) all sequences in which all subsets of variables of a certain size are fed to a software component.

The combinatorial design used to test combinations of values of variables is the Covering Array (CA) defined as CA(N ; t, k, v), which is a matrix of the size N × k, where N is the number of tests, k is the number of variables, v is the number of possible values of each variable, and t is the size of the desired interaction. The combinatorial design used to exercise the order in which the input variables are fed to a system is called Sequence Covering Array (SCA) defined as SCA(M ; t, k), which is a matrix of the size M xk, where M is the number of possible orders, k is the number of input variables, and t is the size of the subsequences of input variables to be covered at least once.

As an optimization problem: a) the problem of constructing an optimal CA(N ; t, k, v) aims to minimize the value of N , maintaining the coverage of all the combinations of values of each t of the k input variables, at least once (each test in a CA belongs to the set vk); b) the problem of constructing an optimal SCA(M ; t, k) aims to minimize the value of M, satisfying the coverage of all subsequences for each t of the k input variables (each test in an SCA belongs to the set of k! permutations).

There are few optimal known cases for CAs and SCAs, for instance, CA(vt; t, k + 1, v) where v is a prime power and SCA(t!; t; t + 1) for t{3, 5, 6}, but in general, the problems of constructing optimal CAs and optimal SCAs are hard combinatorial optimization problems, so it is desirable to use optimization algorithms to construct both combinatorial designs that are nearly optimal ones.

In this Special Issue of Mathematics papers are welcomed that report: a) novel constructions that use greedy, metaheuristic, and/or exact approaches to construct CAs and SCAs; and b) novel applications of CAs and/or SCAs.

Dr. Jose Torres-Jimenez
Guest Editor

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Keywords

  • combinatorial optimization
  • covering array
  • optimization problems
  • constructing covering arrays
  • sequence covering arrays

Published Papers (1 paper)

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15 pages, 267 KiB  
Article
New Upper Bounds for Covering Arrays of Order Seven
by Jose Torres-Jimenez and Idelfonso Izquierdo-Marquez
Mathematics 2024, 12(12), 1908; https://doi.org/10.3390/math12121908 - 20 Jun 2024
Viewed by 305
Abstract
A covering array is a combinatorial object that is used to test hardware and software components. The covering array number is the minimum number of rows needed to construct a specific covering array. The search for better upper bounds for covering array numbers [...] Read more.
A covering array is a combinatorial object that is used to test hardware and software components. The covering array number is the minimum number of rows needed to construct a specific covering array. The search for better upper bounds for covering array numbers is a very active area of research. Although there are many methods for defining new upper bounds for covering array numbers, recently the use of covering perfect hash families has significantly improved a large number of covering array numbers for alphabets that are prime powers. Currently, excellent upper bounds have been reported for alphabets 2, 3, 4, and 5; therefore, the focus of this article is on defining new upper bounds on the size of covering arrays for the alphabet seven using perfect hash families. For this purpose, a greedy column extension algorithm was constructed to increase the number of columns in a covering perfect hash family while kee** the number of rows constant. Our greedy algorithm begins with a random covering perfect hash family containing only eight columns and alternates between adding and removing columns. Adding columns increases the size of the covering perfect hash family while removing columns reduces the number of missing combinations in covering perfect hash families with different column counts. The construction process continues with the covering perfect hash family with the smallest number of columns being refined (i.e., missing combinations reduced). Thus, columns are dynamically added and removed to refine the covering perfect hash families being built. To illustrate the advantages of our greedy approach, 152 new covering perfect hash families of order seven with strengths 3, 4, 5, and 6 were constructed, enabling us to improve 12,556 upper bounds of covering array numbers; 903 of these improvements are for strength three, 8910 for strength four, 1957 for strength five, and 786 for strength six. Full article
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