<Ul> <Li> In density estimation, the unknown parameter is probability density itself . The loss function is typically chosen to be a norm in an appropriate function space . For example, for L norm, </Li> </Ul> <Li> In density estimation, the unknown parameter is probability density itself . The loss function is typically chosen to be a norm in an appropriate function space . For example, for L norm, </Li> <Dl> <Dd> <Dl> <Dd> L (f, f ^) = ∥ f − f ^ ∥ 2 2, (\ displaystyle L (f, (\ hat (f))) = \ f - (\ hat (f)) \ _ (2) ^ (2) \,,) </Dd> </Dl> </Dd> </Dl> <Dd> <Dl> <Dd> L (f, f ^) = ∥ f − f ^ ∥ 2 2, (\ displaystyle L (f, (\ hat (f))) = \ f - (\ hat (f)) \ _ (2) ^ (2) \,,) </Dd> </Dl> </Dd>

Quadratic functions can not be used as models