code: def history(self):
          
          history = OrderedDict()
          for cycle in self:
              d = cycle.last_iteration
              for k, v in d.items():
                  if k in history:
                      history[k].append(v)
                  else:
                      history[k] = [v]
  
          # Convert to numpy arrays.
          for k, v in history.items():
              history[k] = np.array(v)
  
          return history
docs: Ordered Dictionary of lists with the evolution of
          the data as function of the relaxation step.