When we have to solve a complex problem, that means a problem defined by more than three or four parameters and a problem which deals with a number of objective functions - say three, four, five objective functions - we have to use the theory of Multi-objective Programming. I will introduce this theory with a simple example. Let us imagine that we have to optimise wear and we have to select the stiffness and the pre-load of the return spring of such a mechanism. So if I want a minimum wear it is logical that we can find one parameter set, spring stiffness and spring pre-load in order to minimise wear. So I have one objective and one optimal solution.

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