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Inventory replenishment policies

At each iteration in the simulation, an action can be provided to the system, which consists of the replenishment orders placed on every link in the supply network. This action must be of type Vector{Real} and must be nonnegative of the form: [Arc_1_Material_1, Arc_1_Material_2, ..., Arc_1Material_M, Arc_2_Material_1, ..., Arc_2_Material_M, ..., Arc_A_Material_1, ..., Arc_A_Material_M], where the ordering in the arcs is given by edges(SupplyChainEnv.network) and the ordering in the materials by SupplyChainEnv.materials.

An action vector can be visualized as a NamedArray using show_action(SupplyChainEnv, action):

material ╲ arc │ :Arc_1  :Arc_2 ... :Arc_A
───────────────┼──────────────────────────
:Material_1    │  
:Material_2    │  
...            │
:Material_M    │

The function reorder_policy can be used to implement an inventory reorder policy at each node based its inventory position or echelon stock. Reorder quantities are placed to the node's priority supplier. The reorder policy is applied for each material at each node in reverse topological order. This allows upstream nodes to determine their reorder quantities with information about the reorder quantities placed by their successors (relevant for producer nodes to ensure that raw material replenishments are synced with production orders). The two most common policies used in industry are the (s,S) and (r,Q) policies.

The reorder_policy takes the following inputs and returns an action vector.

  • env::SupplyChainEnv: inventory management environment
  • reorder_point::Dict: the s or r parameter in each node for each material in the system. The keys are of the form (node, material).
  • policy_param::Dict: the S or Q parameter in each node for each material in the system. The keys are of the form (node, material).
  • policy_type::Union{Symbol, Dict}: :rQ for an (r,Q) policy, or :sS for an (s,S) policy. If passing a Dict, the policy type should be specified for each node (keys).
  • review_period::Union{Int, AbstractRange, Vector, Dict}: number of periods between each inventory review (Default = 1 for continuous review.). If a AbstractRange or Vector is used, the review_period indicates which periods the review is performed on. If a Dict is used, the review period should be specified for each (node, material) Tuple (keys). The values of this Dict can be either Int, AbstractRange, or Vector. Any missing (node, material) key will be assigned a default value of 1.
  • min_order_qty::Union{Real, Dict}: minimum order quantity (MOQ) at each supply node. If a Dict is passed, the MOQ should be specified for each (node, material) Tuple (keys). The values should be Real. Any missing key will be assigned a default value of 0.
  • order_multiples::Union{Real, Dict}: size increments for each order (default is -1, which means no constraint on order sizes). If a Dict is passed, the order multiples should be specified for each (node, material) Tuple (keys). The values should be Real. Any missing key will be assigned a default value of -1 (meaning no order multiples enforced).
  • adjust_expected_consumption::Bool: indicator if the reorder point should be increased (temporarilly) at a producer node by the expected raw material consumption for an expected incoming production order.