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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def ffDTF(self):
 """Full frequency directed transfer function. .. math:: \mathrm{ffDTF}_{ij}(f) = \\frac{H_{ij}(f)}{\sqrt{\sum_f H_{i:}(f) H_{i:}'(f)}} References A. Korzeniewska, M. Mańczak, M. Kaminski, K. J. Blinowska, S. Kasicki. Determination of information flow direction among brain structures by a modified directed transfer function (dDTF) method. J. Neurosci. Meth. 125(1-2):
 195-207, 2003. """

        H = self.H()
        return np.abs(H * self.nfft / np.sqrt(np.sum(H * H.conj(), axis=(1, 2),
                                                     keepdims=True)))