sys . Since the original sine-DFT should be a unitary transformation (see Eqs. 10 and 11), then we can assume |x| 2 = x T x = y T y = |y| 2 , because upon unitary transformation the vector norm should be conserved. However, such approximation (y T y = M • δ 2 sys ) does not account for the weight matrix. To do that, we can replace y T y with a weighted analog, i.e., y T W y, which is now a dimension-less vector. Therefore, to restore dimensionality, we can normalize this quantity by the mean value of all weights