Narrow Results

We study an optimal consumption and investment problem in a possibly incomplete market with general, not necessarily convex, stochastic constraints. We provide explicit solutions for investors with exponential, logarithmic as well as power utility and show that they are unique if the constraints are convex. Our approach is based on martingale methods that rely on results on the existence and uniqueness of solutions to BSDEs with drivers of quadratic growth.

This paper deals with the problem of optimal consumption and portfolio for a generalized Black and Scholes market where the volatility is driven by a standard Brownian motion and by a fractional Brownian motion in the same time.

We consider the optimal investment and consumption policy for a constant absolute risk averse investor who faces fixed and/or proportional transaction costs when trading a stock and maximizes his expected utility from intertemporal consumption. We show that the Hamilton-Jacobi-Bellman PDE with free boundaries can be reduced to an ODE, which greatly simplifies the problem. Using the stochastic impulse and singular control techniques, we then derive the optimal investment and consumption policy. In particular, when there are both fixed and proportional costs, it is shown that the optimal stock investment policy is to keep the dollar amount invested in the stock between two constant levels and upon reaching these two thresholds, the investor jumps to the corresponding optimal target level.