Before revision:  Under the specific condition on model parameters , we show that the value function is a C^2 solution of the HJB equation and derive the optimal investment strategy in terms of second-order ordinary differential equations.
After revision:  We derive the optimal investment strategy under the specific condition on model parameters , we show that the value function is a C^2 solution of the HJB equation and derive the optimal investment strategy in terms of second-order ordinary differential equations.