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43<br />

repeated to change the population until the first chromosome of the population obtains<br />

a good enough fitness value f(x). However, if repeated too many times, these<br />

operations will create a large number of chromosomes that is above the preset<br />

population size. To solve this problem, once the number of chromosomes increases up<br />

to a critical value n, we will kill off half of the population.<br />

3.6.1 Representations<br />

This section defines the <strong>genetic</strong> representations of the chromosomes, the genes,<br />

and the population.<br />

3.6.1.1 Chromosomes<br />

A chromosome is a solution, in our case a timetable of the university. The<br />

timetable contains a number of sub-timetables of classrooms. Each classroom has its<br />

own sub-timetable.<br />

Classroom i<br />

Hour Mon Tue Wed Thu Fri<br />

08:00-09:00 Course 1 Course 2<br />

09:00-10:00 Course 1 Course 2<br />

10:00-11:00 Course 1 Course 2<br />

11:00-12:00<br />

13:00-14:00 Course 3<br />

14:00-15:00 Course 3<br />

15:00-16:00 Course 4<br />

16:00-17:00 Course 4<br />

FIGURE 3-7 Sub-timetable of a classroom<br />

We use a classroom as a ‘storage space’. Courses are scheduled to the time-slots<br />

<strong>for</strong> each classroom. This direct representation creates a visual view. Here courseis are<br />

courses that are divided into sections. These sections are assigned to be taught by<br />

particular lecturer and studied by a class of students. A look at the data relations in the<br />

database, we have course → lecturer, course→ class. This is a good foundation <strong>for</strong><br />

checking the hard and soft constraint conflicts.<br />

The Figure 3-8 illustrates an entire chromosome.

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