 
Summary: Chapter 2
Evolutionary Algorithms with String
Representations
The simplest evolutionary algorithms store the members of their evolving populations as
fixed length strings over a simple alphabet. This type of evolutionary algorithm is called a
string evolver. A simple evolutionary algorithm may solve a simple problem or a difficult
one. The difficulty of the problem a string evolver is solving depends primarily on the fitness
function and, to a lesser degree, on the way the variation operators are designed. Another
important factor is the population size.
2.1 The Simple Evolutionary Algorithm
We begin by defining a number of terms. An alphabet is a set of characters. A string is a
finite sequence of characters over (with characters from) some alphabet.
Example 2.1 The binary alphabet is {0, 1}. Examples of strings over the binary alphabet
are 0, 01, and 10101001.
Definition 2.1 If A is an alphabet then An
is the set of all strings of length n over A. The
set of all strings over A is denoted A
.
Example 2.2 {a, b, c}2
= {aa, ab, ac, ba, bb, bc, ca, cb, cc}
