docs: def dre_drho0(self, pars):
          r""" Compute partial derivative of real parts with respect to
          :math:`\rho_0`
  
          :math:`\frac{\partial \hat{\rho'}(\omega)}{\partial \rho_0} = 1 -
          \frac{m (\omega \tau)^c cos(\frac{c \pi}{2}) + (\omega \tau)^c}{1 + 2
          (\omega \tau)^c cos(\frac{c \pi}{2}) + (\omega \tau)^{2 c}}`
  
          Note that partial derivatives towards :math:`\rho_0` are 1D, in
          contrast to the other parameter derivatives, which usually return 2D
          arrays!
  
          Returns
          -------
          dre_drho0: :class:`numpy.ndarray`
              Size N (nr of frequencies) array with the derivatives
  
          """
          self._set_parameters(pars)
          numerator = self.m * self.otc * (np.cos(self.ang) + self.otc)
          term = numerator / self.denom
          specs = np.sum(term, axis=1)
  
          result = 1 - specs
          return result