code: def momentum(self, exponent=1, errorrequested=True):
          
          y = self.Intensity * self.q ** exponent
          m = np.trapz(y, self.q)
          if errorrequested:
              err = self.Error * self.q ** exponent
              dm = errtrapz(self.q, err)
              return ErrorValue(m, dm)
          else:
              return m
docs: Calculate momenta (integral of y times x^exponent)
          The integration is done by the trapezoid formula (np.trapz).
  
          Inputs:
              exponent: the exponent of q in the integration.
              errorrequested: True if error should be returned (true Gaussian
                  error-propagation of the trapezoid formula)