but may have poor off-design characteristics. It is important, therefore, that the designer ensures robustness of the solution, defined as the system’s insensitivity to any variation of the input parameters. It is quite possible that the optimal solution will not be the most stable solution.

In the example shown here there is a global optimum at point A, and a local optimum at point B. However, any small variations in the input parameters will cause the performance to drop off markedly around A. The performance of B may not be as good in absolute terms, but it is much more robust, since small changes in the input values do not cause drastic performance degradation.