Peter Lakner

Optimal trading strategy for an investor: the case of partial information

We shall address here the optimization problem of an investor who wants to maximize the expected utility from terminal wealth. The novelty of this paper is that the drift process and the driving Brownian motion appearing in the stochastic differential equation for the security prices are not assumed to be observable for investors in the market. Investors observe security prices and interest rates only. The drift process will be modelled by a Gaussian process, which in a special case becomes a multi-dimensional mean-reverting Ornstein-Uhlenbeck process. The main result of the paper is an explicit representation for the optimal trading strategy for a wide range of utility functions.

Optimal Bankruptcy Time and Consumption/Investment Policies on an Infinite Horizon with a Continuous Debt Repayment Until Bankruptcy

In this paper we consider the optimization problem of an agent who wants to maximize the total expected discounted utility from consumption over an infinite horizon. The agent is under obligation to pay a debt at a fixed rate until he/she declares bankruptcy. At that point, after paying a fixed cost, the agent will be able to keep a certain fraction of the present wealth, and the debt will be forgiven. The selection of the bankruptcy time is taken to be at the discretion of the agent. The novelty of this paper is that at the time of bankruptcy the wealth process has a discontinuity, and that the agent continues to invest and consume after bankruptcy. We show that the solution of a free boundary problem satisfying some additional conditions is the value function of the above optimization problem. Particular examples such as the logarithmic and the power utility functions will be provided, and in these cases explicit forms will be given for the optimal bankruptcy time, investment and consumption processes.

High Frequency Asymptotics for the Limit Order Book

We study the one-sided limit order book corresponding to limit sell orders and model it as a measure-valued process. Limit orders arrive to the book according to a Poisson process and are placed on the book according to a distribution which varies depending on the current best price. Market orders to buy periodically arrive to the book according to a second, independent Poisson process and remove from the book the order corresponding to the current best price. We consider the above described limit order book in a high frequency regime in which the rate of incoming limit and market orders is large and traders place their limit sell orders close to the current best price. Our first set of results provide weak limits for the unscaled price process and the properly scaled measure-valued limit order book process in the high frequency regime. In particular, we characterize the limiting measure-valued limit order book process as the solution to a measure-valued stochastic differential equation. We then provide an analysis of both the transient and long-run behavior of the limiting limit order book process.

Optimal Control of a Mean-Reverting Inventory

Motivated by empirical observations, we assume that the inventory level of a company follows a mean-reverting process. The objective of the management is to keep this inventory level as close as possible to a given target; there is a running cost associated with the difference between the actual inventory level and the target. If inventory deviates too much from the target, management may perform an intervention in the form of either a purchase or a sale of an amount of the goods. There are fixed and proportional costs associated with each intervention. The objective of this paper is to find the optimal inventory levels at which interventions should be performed as well as the magnitudes of the interventions to minimize the total cost. We solve this problem by applying the theory of stochastic impulse control. Our analysis yields the optimal policy, which at times exhibits a behavior that is not intuitive.

Optimal Production Management When Demand Depends on the Business Cycle

We assume that the cumulative consumer demand for an item follows a Brownian motion, with both the drift and the variance parameters modulated by a continuous-time Markov chain that represents the regime of the economy. The management of the company would like to maintain the inventory level as close as possible to a target inventory level and would also like to produce at a rate that is as close as possible to a target production rate. The company is penalized for deviations from the target levels, and the objective is to minimize the total discounted penalty costs. We consider two models. In the first model the management of the company knows the state of the economy, whereas in the second model the management does not know it. We solve both problems and obtain the optimal production policy and the minimal total expected discounted cost. Furthermore, we compare the total expected discounted costs of the two models and determine the value of knowing the regime of the economy. We also solve the above problems in the case when the consumer demand rate follows a geometric Brownian motion modulated by a continuous-time Markov chain that represents the regime of the economy.

Almost sure characterization of Martingales

Let be an arbitrary set with be a complete filtered probability space such that F 0 is trivial and complete; χ be a countable family of real adapted stochastic processes on Ξ. We provide a necessary and sufficient condition for the existence of a probability measure Q, equivalent to the original measure P, under which every process is a martingale. Furthermore, this condition is invariant under substitution of P with an equivalent probability measure; hence the theorem characterizes those real adapted stochastic processes on Ξ which can become martingales under some equivalent probability measure. The theorem we present allows us also to give a satisfactory solution to the so called Fundamental Problem of Asset Pricing which arises in Mathematical Finance; we further provide the financial interpretation of the “no-free-lunch” condition which is equivalent to the existence of a “risk-neutral measure”.