code: def dre_dtau(self, pars):
          r
          self._set_parameters(pars)
          # term 1
          num1 = self.c * self.w * self.otc1 * np.cos(self.ang)
          term1 = num1/self.denom
  
          # term 2
          num2a = self.otc * np.cos(self.ang)
          num2b = 1 + num2a
          denom2 = self.denom ** 2
          term2 = num2b / denom2
  
          # term 3
          term3 = 2 * self.c * self.w * self.otc1 * np.cos(self.ang) + self.otc2
  
          result = self.sigmai * self.m * (term1 + term2 * term3)
  
          return result
docs: r"""
          :math:Add formula