 Typically, is some subset of the Euclidean space , often specified by a set of "constraints", equalities or inequalities that the members of have to satisfy.The domain of is called the "search space" or the "choice set", while the elements of are called "candidate solutions" or "feasible solutions".The function is called, variously, an "objective function", a "loss function" or "cost function" (minimization), a "utility function" or "fitness function" (maximization), or, in certain fields, an "energy function" or "energy functional".