Hands-On Genetic Algorithms with Python

Hard constraints versus soft constraints

When solving the nurse scheduling problem, we should bear in mind that some of the constraints represent hospital rules that cannot be broken. A schedule that contains one or more violations of these rules will be considered invalid. More generally, these are known as hard constraints.

The nurses' preferences, on the other hand, can be considered soft constraints. We would like to adhere to them as much as possible, and a solution that contains no violation or fewer violations of these constraints is considered better than one that contains more violations. But a violation of these constraints does not invalidate the solution.

In the case of the N-Queens problem, all the constraints – row, column, ...