## 4 Review of Literature
### Supply and Delivery in Routing Optimisation Problems
#### 4.1.4 Metaheuristics in Supply and Delivery VRPs
The former model is based on the the assumption where one affected area only needs to be served by one distribution centre, while the latter deals the problem with the flexibility of split delivery allowing for more than one distribution centre to serve one affected site. In this problem, a two level planning approach is considered. First, the location of distribution centre is sought for with different capacity to be considered. The second level focused on distribution of the commodity through an optimised route. A multi-objective is defined for the problem that is based on this level of operations. The first level sought to minimise the cost of setting up warehouses and distribution centre, as well as the cost of storing commodity. While the second phase aims to minimise the travel cost incurred by routing the vehicle for relief distribution, the travel time as well as maximising the route reliability between crucial nodes. As researched in [76], the model is solved by the NSGA-II and MOPSO. Both of the solutions were compared through 35 instances, whereby the NSGA-II proved to be better when addressing model with uncertain parameter. Meanwhile, MOPSO is more efficient when solving the deterministic model. The problem of scheduling the Disaster Medical Assistance Team (DMAT) and the optimal relief distribution simultaneously is considered in [82]. The intention is to coordinate both operations so as to allocate limited resources in the most efficient way in times of disaster. The objective is to minimise the total service completion time. The problem is further structurally analyses to decompose it into two types of problem formulation: P1 and P2. Looking at the DMAT routing alone without the relief aid allocation and distribution, the initial problem would be reduced to Time Dependant VRP (TDVRP) (P1) with the objective to reduce the total completion time. P1 could be solved to near optimality through the Rolling Horizon (RH) algorithm. The problem is then reduced to a special case of the original problem (P2), where the objective is to minimise the total tardiness of delivering relief aid. Based on this analysis, a solution approach is proposed, where P1 is solved by the modified Artificial Bee Colony (ABC) algorithm. Next, by applying the DMAT route to the initial solution, P2 is then solved by the RH algorithm. This work concludes with a numerical experiment that is based on the 2016 Kumamoto Earthquake in Japan, where the solution was obtained in practical time. Ref. [83], on the other hand, addressed both the CVRP as well as the Split Delivery VRP (SDVRP), while trying to minimise with five separate models each: the total number of vehicles, the total travel time, the latest arrival time, the demand weighted arrival time, and the summation of arrival time. The problem is first modelled as a deterministic model serving as a basic model for the robust counterpart. Depending on the objective functions, an adjustment is made to the deterministic model by changing the objective function and adding corresponding constraints if necessary. The same process is applied to both the deterministic CVRP and SDVRP model. Similarly, respective robust counterparts are also developed to adopt the robust optimisation approach. A two stage heuristic-metaheuristic is proposed based on a known construction heuristic and tabu search. An extended insertion heuristic is applied to the complicating constraint, namely the capacity constraint in robust CVRP formulation. Meanwhile, two additional algorithms are added in order to account for robust SDVRP constraint revolving the increase demand and travel time. A good initial solution is then obtain for tabu search to improved upon. Through their work, it is shown that the robust SDVRP model was able to reach the goal better when compared to CVRP when dealing with uncertain travel time and demands. Ref. [84] focused on the cooperative delivery among vehicle, where product transshipment is allowed in a dynamic setting for disaster relief aid.