code: def dim_dtau(self, pars):
          r
          self._set_parameters(pars)
          # term 1
          num1 = -self.m * (self.w ** self.c) * self.c\
              * (self.tau ** (self.c - 1)) * np.sin(self.ang)
          term1 = self.sigmai * num1 / self.denom
  
          # term 2
          num2a = -self.m * self.otc * np.sin(self.ang)
          num2b = 2 * (self.w ** 2.0) * self.c * (self.tau ** (self.c - 1)) *\
              np.cos(self.ang)
          num2c = 2 * self.c * (self.w ** (self.c * 2)) *\
              (self.tau ** (2 * self.c - 1))
          term2 = self.sigma0 * num2a * (num2b + num2c) / (self.denom ** 2)
  
          result = term1 + term2
  
          return result
docs: r"""
          :math:Add formula