Activities and periods

All activities within the network occur within a particular period. Although activities such as imports and exports may occur on particular dates, for calculation and reporting purposes the results are shown in the period which the date occurs in.

For example, period 2 may span one week. An activity could be stated to start after Tuesday, and end before Saturday, and take one day. That is, it takes one day to complete the activity and the activity itself must be completed between Tuesday and Saturday. Although the activity has specific times associated with it, during optimization the activity is associated only with period 2. The actual time at which this activity should occur is not determined by the optimization, only the amount of material that should move in the period.

Periods can be used to divide the network schedule into different timespans, allowing granular control of the movements, so that well-defined activities occurring soon are included in short periods in the near future, whereas poorly defined activities far in the future can be defined in longer periods further in time.

The above diagram shows activities in different periods for the grade Gasoline 95. Both Lake Charles and Assab produce Gasoline 95, and both plants have a local demand for this material. It is also possible to ship final product from Assab to Lake Charles if required.

In the first period, both Lake Charles and Assab manufacture enough Gasoline 95 to satisfy their local demand (at each location, the supply node amount matches the demand node requirement). Therefore it is not required to move any material between Assab and Lake Charles.

In the second period, the demand at Lake Charles is increased, while the supply at the same location is reduced. Therefore to satisfy the extra demand it is necessary to ship some material from Assab to Lake Charles.

In the third period the transfer between plants is not allowed. Therefore each plant can only satisfy its local market demand.

Activities spanning periods

Activities may span two or more periods. When an activity spans more than one period, the amount is pro-rated across the periods, so that the total amount is proportionally allocated to each period.

For example, suppose that periods 2 and 3 both span one week. An activity lasting two days could be stated to start after Saturday, and must end before Wednesday. This activity would be pro-rated to move 40% of the material in period 2, and 60% in period 3.