code: def efficiency_capacity_demand_difference(slots, events, X, **kwargs):
      
      overflow = 0
      for row, event in enumerate(events):
          for col, slot in enumerate(slots):
              overflow += (event.demand - slot.capacity) * X[row, col]
      return overflow
docs: A function that calculates the total difference between demand for an event
      and the slot capacity it is scheduled in.