Mathematical optimisation often involve using the differential of the fitness function. In simple cases it may be possible to solve tofind the parameters such that the partial differential (slope) in every dircetion is zero. Alteratuvely, if the differentials can be calculated, one can use gradient descent to move in the direction of maximium imporvement of fitness. Typically these techniques only work when the parameters are continuous variables the fitness function is continuous and differentiable – that is no sudden jumps or changes in slope.
Used in Chap. 4: page 51