Two different approaches can be used to introduce constraints. We can directly employ a penalty function approach substituting the objective function with another one that takes into account constraints violation. A different approach is the expression based strategy. According to this strategy infeasible designs can be replaced by a chromosome that incorporates features of the feasible design. If we consider A as the best feasible design and B as an infeasible design we create bit-by-bit operator that substitute some position into the string that defines the infeasible design.

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