2.9 Replanning

Sometimes it is necessary to update or extend a solution generated by the optimiser. Reasons for this include:

• Orders being added.
• Orders being cancelled.
• Order details (e.g. weights, volumes, time windows etc.) changing.
• Vehicles being added to the fleet.
• Vehicles being removed from the fleet.
• Vehicle / driver availability changing.

When this happens, it is often desirable to maintain as much of the existing solution as practicable. For example, when loads are being assembled at the loading docks of a warehouse, altering the original plan too much may unduly affect warehouse operations.

This usage of the optimiser is called replanning. When replanning, an updated scenario is extended with information about the assignments and sequencing in a previous solution. The optimiser can be configured to minimise the differences between the solution it generates and the previous solution while incorporating any changes.

The following global parameters control the degree and manner to which deviations from the existing solution can occur.

1. Previous-Vehicle Fixed Reward

   This parameter gives the strength of the preference for orders to remain on their previously assigned vehicles.

2. Previous-Vehicle Weight Reward

   This parameter gives the strength of the preference for heavier orders to remain on their previously assigned vehicles.

3. Previous-Vehicle Volume Reward

   This parameter gives the strength of the preference for larger orders to remain on the their previously assigned vehicles.

Each of the above rewards is a form of hidden cost and their effect is cumulative.