def PSD_sym_KL(u, v):
    """ Calculate the symmetric KL divergence between two spectral densities
        j = sum( u / v + v / u - 2)

        Args:
            u       1d array        PSD array
            v       1d array        PSD array
    """
    n = len(v)
    j = (1 / n) * (u / v + v / u - 2).sum()

    return j