Title:

Genetic algorithms : sequential and parallel implementations and case studies.

Practical issues concerning the implementation and application of genetic algorithms
to a number of optimisation problems are the main subjects dealt with in this thesis.
Genetic algorithms (GAs) are an attractive class of computational models that attempt
to mimic the mechanisms of natural evolution to solve problems in a wide variety of
domains. A general purpose genetic algorithm toolkit is developed and applied to the
Steiner Problem in Graphs and the Radio Link Frequency Assignment Problem. The
toolkit is then extended to cover a large number of parallel genetic algorithm models
which are then compared. Solutions for the two case studies are presented with each
of the parallel GAs.
The thesis begins with a general introduction to genetic algorithms. Holland's
original genetic algorithm is described and it's workings illustrated on a simple
function minimisation problem. The notion of a schema or similarity template as a
basic building block in genetic algorithms is introduced and the schema theory
presented. A description of important theoretical results is given and the introduction
to genetic algorithms continues with practical issues that are dealt with in the second
chapter.
The basic components of a modern genetic algorithm are outlined and
examples for important components, as found in the Jiterature, are given. The second
chapter concludes with the description of a number of applications of genetic
algorithms to areas such as function optimisation, combinatorial optimisation, genetic
programming, process control and classifier systems.
In Chapter 3, the sequential GA toolkit, GAmeter, is described. The General
Search paradigm around which the toolkit is implemented is introduced. Notable
characteristics of the genetic algorithms kernel and the user interface are mentioned.
A popular function optimisation problem is used to illustrate important aspects of
genetic algorithms and aspects specific to the toolkit.
The Steiner Tree problem in graphs is the first of two case studies examined in
detail in this thesis. This is a popular NPcomplete problem with a range of
applications in areas such as communications, scheduling and printed circuit design.
A survey of standard techniques, such as simplification methods, exact algorithms and
heuristics is given. Two possible representations for solving it using genetic
algorithms are described and applied to a wellknown set of problems. Chapter 4
concludes with a comparison of the best GA technique with other heuristics for this
problem.
The Radio Link Frequency Assignment Problem, described in Chapter 5, is
the second case study investigated in this thesis. Genetic algorithms were applied to
this problem as part of a EUCLID (European Cooperation for the Long Term in
Defence) funded multinational study to compare exact and heuristic techniques for
hard combinatorial problems associated with military applications. A number of
approaches used to solve this highly constrained, hard problem for genetic algorithms
are described. These include a range of new genetic operators and catalytic terms that
are added to the fitness function. Apart from the direct approach to solving this
problem using genetic algorithms, for which the majority of operators and catalytic
terms apply, an indirect approach which combines genetic algorithms with
backtracking is described. The possibility of using a meta genetic algorithm to chose
the best of a multitude of options, e.g. genetic operators and parameter settings for a
GA applied to the Radio Link Frequency Assignment Problem is investigated. Results
are reported for two sets of problems that were used by all participants in this project.
An overview of the techniques investigated for this project is given and the chapter
concludes with comparisons between all these techniques.
In Chapter 6, an overview of general aspects in parallel processing is given.
Parallel computer architectures, parallel programming paradigms and performance
measurement are the main subjects dealt with in this chapter. Special emphasis is
given to material relevant to the investigation on parallel genetic algorithms,
presented in the following chapter.
In Chapter 7, parallel genetic algorithms are examined in some detail. A
number of parallel GA models are described and classified according to whether they
are designed around the sequential GA or around a more natural model. A ParallelSequential
General Search paradigm is presented that unifies the various parallel
models and is used to extend the GA toolkit into a parallel GA toolkit for a parallel
system based on Transputers. The parallel GA models are applied to problems from
both of the case studies considered in this thesis. A comparison between the various
parallel GA models concludes this chapter.
The thesis finishes with a summary of a number of conclusions drawn from
this research together with some suggestions for how this work may be continued in
the future.
