Applied Mathematics and Optimization, Vol.76, No.2, 415-428, 2017
Controlling the Occupation Time of an Exponential Martingale
We consider the problem of maximizing the expected amount of time an exponential martingale spends above a constant threshold up to a finite time horizon. We assume that at any time the volatility of the martingale can be chosen to take any value between and , where . The optimal control consists in choosing the minimal volatility when the process is above the threshold, and the maximal volatility if it is below. We give a rigorous proof using classical verification and provide integral formulas for the maximal expected occupation time above the threshold.