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