Portfolio Allocation under the Vendor Managed Inventory: A Markov Decision Process

Markov decision processes have been applied in solving a wide range of optimization problems over the years. This study provides a review of Markov decision processes and investigates its suitability for solutions to portfolio allocation problems under vendor managed inventory in an uncertain market environment. The problem was formulated in the frame work of Markov decision process and a value iteration algorithm was implemented to obtain the expected reward and the optimal policy that maps an action to a given state. Two challenges were examined –the uncertainty about the value of the item which follows a stochastic model and the small state/action spaces that can be solved via value iteration. It was observed that the optimal policy is expected to always short the stock when in state 0 because of its large return. However, while the return is not as large as in state 0, the probability of staying in state 2 is high enough that the vendor should long the stock because he expects high reward for several periods. We also obtained the expected reward for each state every ten iterations using a discount factor of λ = 0.95. In spite of the small state/action spaces, the vendor is able to optimize its reward by the use of Markov decision process.

Keywords
Portfolio Allocation; Vendor Managed Inventory; Markov Decision Process; Value Iteration; Expected Reward; Optimal Policy