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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 pCOH(self):
 """Partial coherence. .. math:: \mathrm{pCOH}_{ij}(f) = \\frac{G_{ij}(f)} {\sqrt{G_{ii}(f) G_{jj}(f)}} References P. J. Franaszczuk, K. J. Blinowska, M. Kowalczyk. The application of parametric multichannel spectral estimates in the study of electrical brain activity. Biol. Cybernetics 51(4):
 239-247, 1985. """

        G = self.G()
        # TODO: can we do that more efficiently?
        return G / np.sqrt(np.einsum('ii..., jj... ->ij...', G, G))