However, for the sake of dealing with the math that follows, it is more convenient to deal with time limits in the signal itself rather than time limits in the bounds of the integral. As such, we have an alternative representation of the average power, where x T ( t ) = x ( t ) w T ( t ) and w T ( t ) is unity within the arbitrary period and zero elsewhere. P = lim T → → ∞ ∞ 1 T ∫ ∫ − − ∞ ∞ ∞ ∞ | x T ( t ) | 2 d t . Clearly, in cases where the above expression for P is non-zero, the integral must grow without bound as T grows without bound. That is the reason why we cannot use the energy of the signal, which is that diverging integral, in such cases.