5. PLANS VARIATION (RE-PLANNING)

The re-planning is responsible for making sure that every agent explores its solution space. This happens by duplicating an existing plan of an agent, varying (mutating) the copy, and executing and scoring it in the next iteration. Each re-planning module takes charge for a specific part in the optimization process. As an example, the Router module calculates the routes of a plan based on the amount of traffic from the last traffic flow simulation. The Time Allocation Mutator module modifies departure times and activity durations of a daily plan. This module varies the corresponding times randomly. Additional modules could change activities' locations, or change the sequence of activities. An important fact is that all these modules work independently from each other. This allows one to add an arbitrary number of re-planning modules to the optimization process.

A characterization of modules is whether they modify a plan randomly (Random Mutation) or whether they search for the best solution based on the results of the last traffic flow simulation (Best Response). The former has the advantage not to use any significant amount of computing power. Additionally, it searches—sooner or later—over the complete search domain. The disadvantage is that such modules require (too) many iterations until the optimization relaxes. Best Response modules on the other hand help to relax the system much faster, but they are usually more complex and computationally intensive.