r"""
        :math:`\frac{\partial \hat{\rho'}(\omega)}{\partial m} = - \rho_0 m
        (\omega \tau)^c \frac{(cos(\frac{c \pi}{2}) + (\omega \tau)^c)}{1 + 2
        (\omega \tau)^c cos(\frac{c \pi}{2}) + (\omega \tau)^{2 c}}`

def dre_dm(self, pars):
        r"""
        :math:`\frac{\partial \hat{\rho'}(\omega)}{\partial m} = - \rho_0 m
        (\omega \tau)^c \frac{(cos(\frac{c \pi}{2}) + (\omega \tau)^c)}{1 + 2
        (\omega \tau)^c cos(\frac{c \pi}{2}) + (\omega \tau)^{2 c}}`
        """
        self._set_parameters(pars)
        numerator = -self.otc * (np.cos(self.ang) + self.otc)
        result = numerator / self.denom
        result *= self.rho0
        return result