  In this paper, we attempt to introduce the Bellman principle for a discrete
time multi-period mean-variance model. Based on this new take on the Bellman
principle, we obtain a dynamic time-consistent optimal strategy and related
efficient frontier. Furthermore, we develop a varying investment period
discrete time multi-period mean-variance model and obtain a related dynamic
optimal strategy and an optimal investment period. This paper compares the
highlighted dynamic optimal strategies of this study with the 1/n equality
strategy, and shows that we can secure a higher return with a smaller risk
based on the dynamic optimal strategies.
