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Earthquake Engineering Research - HKU Libraries - The University ...

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295<br />

Genetic algorithm starts from a group of individuals, namely population, and its size is noted as N.<br />

<strong>The</strong>n the primal parameters of model can be given by:<br />

S, = S imin + ^(Staax - Si rai n) (i=l,2,...,M) (2.3)<br />

in which, S imax and Si min are respectively the upper and lower limits of parameter S, that need to be<br />

identified. ^ is a uniform distributed random number between 0 and 1.<br />

2.2 Genetic Operation<br />

2.2.1 Selection<br />

After the initial population was obtained, the objective function of every model can be calculated by<br />

(2.1). Objective function is the direct express of the quality of the model, and is the basic standard to<br />

distinguish the individuals. <strong>The</strong>re are many methods to express the quality of individual in genetic<br />

algorithm, and the relative fitness used in the paper is<br />

(2.4)<br />

where T is a constant, £ is a random distributed variable, and £e[0,l]. If ^\|/, <

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