Know the principle of operation (algorithm) of the genetic algorithm approach ([2]: p. 99)

Database System Concepts
7th Edition
ISBN:9780078022159
Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
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Know the principle of operation (algorithm) of the genetic algorithm approach ([2]: p. 99)

Evolution Inside Your Computer
that you do not need to know how to solve a problem; you only need to know how to
encode it in a way the genetic algorithm mechanism can utilize.
Typically, the chromosomes are encoded as a series of binary bits. At the start of a
run, you create a population of chromosomes, and each chromosome has its bits set
at random. The length of the chromosome is usually fixed for the entire popula-
tion. As an example, this is what a chromosome of length twenty may look like:
0101001010010100||||
The important thing is that each chromosome is encoded in such a way that the
string of bits may be decoded to represent a solution to the problem at hand. It may be
a very poor solution, or it may be a perfect solution, but every single chromosome
represents a possible solution (more on the encoding in a moment). Usually the
starting population is terrible, a little like the English cricket team or an American
playing football (sorry, soccer). Anyway, like I said, an initial population of random
bits is created (let's say one hundred for this example), and then you do this (don't
worry about the italicized phrases. I'll be explaining each one in just a moment):
Loop until a solution is found:
1. Test each chromosome to see how good it is at solving the problem and
assign a fitness score accordingly.
2. Select two members from the current population. The probability of being
selected is proportional to the chromosome's fitness-the higher the fitness,
the better the probability of being selected. A common method for this is
called Roulette wheel selection.
3. Dependent on the Crossover Rate, crossover the bits from each chosen chro-
mosome at a randomly chosen point.
4. Step through the chosen chromosome's bits and flip dependent on the
Mutation Rate.
5. Repeat steps 2, 3, and 4 until a new population of one hundred members has
been created.
End loop
Each loop through the algorithm is called a generation (steps 1 through 5). I call the
entire loop an epoch and will be referring to it as such in my text and code.
What's Roulette Wheel Selection?
Roulette wheel selection is a method of choosing members from the population of
chromosomes in a way that is proportional to their fitness-for example, the fitter
99
Transcribed Image Text:Evolution Inside Your Computer that you do not need to know how to solve a problem; you only need to know how to encode it in a way the genetic algorithm mechanism can utilize. Typically, the chromosomes are encoded as a series of binary bits. At the start of a run, you create a population of chromosomes, and each chromosome has its bits set at random. The length of the chromosome is usually fixed for the entire popula- tion. As an example, this is what a chromosome of length twenty may look like: 0101001010010100|||| The important thing is that each chromosome is encoded in such a way that the string of bits may be decoded to represent a solution to the problem at hand. It may be a very poor solution, or it may be a perfect solution, but every single chromosome represents a possible solution (more on the encoding in a moment). Usually the starting population is terrible, a little like the English cricket team or an American playing football (sorry, soccer). Anyway, like I said, an initial population of random bits is created (let's say one hundred for this example), and then you do this (don't worry about the italicized phrases. I'll be explaining each one in just a moment): Loop until a solution is found: 1. Test each chromosome to see how good it is at solving the problem and assign a fitness score accordingly. 2. Select two members from the current population. The probability of being selected is proportional to the chromosome's fitness-the higher the fitness, the better the probability of being selected. A common method for this is called Roulette wheel selection. 3. Dependent on the Crossover Rate, crossover the bits from each chosen chro- mosome at a randomly chosen point. 4. Step through the chosen chromosome's bits and flip dependent on the Mutation Rate. 5. Repeat steps 2, 3, and 4 until a new population of one hundred members has been created. End loop Each loop through the algorithm is called a generation (steps 1 through 5). I call the entire loop an epoch and will be referring to it as such in my text and code. What's Roulette Wheel Selection? Roulette wheel selection is a method of choosing members from the population of chromosomes in a way that is proportional to their fitness-for example, the fitter 99
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