Here, the control variables are denoted by ξ, the scalar-valued objective function by
Q, and the feasible set is denoted by
C. Assuming sufficient continuity, the feasible set can be expressed as a set of — possibly very nonlinear — inequality constraints
where G is a vector-valued function (
G is scalar-valued in case of a single constraint).
In classical optimization,
Q and
G are given explicitly as closed-form expressions of the control variables
ξ. However, design problems and parameter estimation problems often result in objective functions
Q and constraints
G that are not explicitly expressible as closed-form expressions of the control variables
ξ.