code: def relative_error(self):
          
          if self.previous is not None:
              # FIXME
              # Use the maximum strain value -- this is important for error
              #  calculation with frequency dependent properties
              # prev = np.max(self.previous)
              # value = np.max(self.value)
              try:
                  err = 100. * np.max((self.previous - self.value) / self.value)
              except ZeroDivisionError:
                  err = np.inf
          else:
              err = 0
          return err
docs: The relative error, in percent, between the two iterations.