arXiv subjects

Kerem Ugurlu

Publications and source records attributed to Kerem Ugurlu.

8 recordsLinked to original sources

arXiv2019

Robust Utility Maximization with Drift and Volatility Uncertainty

We give explicit solutions for utility maximization of terminal wealth problem $u(X_T)$ in the presence of Knightian uncertainty in continuous time $[0,T]$ in a complete market. We assume there is uncertainty on both drift and volatility of the underlying stocks, which induce nonequivalent measures on canonical space of continuous paths $Ø$. We take that the uncertainty set resides in compact sets that are time dependent. In this framework, we solve the robust optimization problem with logarithmic, power and exponential utility functions, explicitly.

q-fin.MF↗

arXiv2018

Portfolio Optimization with Nondominated Priors and Unbounded Parameters

We consider classical Merton problem of terminal wealth maximization in finite horizon. We assume that the drift of the stock is following Ornstein-Uhlenbeck process and the volatility of it is following GARCH(1) process. In particular, both mean and volatility are unbounded. We assume that there is Knightian uncertainty on the parameters of both mean and volatility. We take that the investor has logarithmic utility function, and solve the corresponding utility maximization problem explicitly. To the best of our knowledge, this is the first work on utility maximization with unbounded mean and volatility in Knightian uncertainty under nondominated priors.

math.OC↗

arXiv2018

Dynamic optimal contract under parameter uncertainty with risk averse agent and principal

We consider a continuous time Principal-Agent model on a finite time horizon, where we look for the existence of an optimal contract both parties agreed on. Contrary to the main stream, where the principal is modelled as risk-neutral, we assume that both the principal and the agent have exponential utility, and are risk averse with same risk awareness level. Moreover, the agent's quality is unknown and modelled as a filtering term in the problem, which is revealed as time passes by. The principal can not observe the agent's real action, but can only recommend action levels to the agent. Hence, we have a \textit{moral hazard} problem. In this setting, we give an explicit solution to the optimal contract problem.

math.OC↗

arXiv2018

Decomposability and time consistency of risk averse multistage programs

Two approaches to time consistency of risk averse multistage stochastic problems were discussed in the recent literature. In one approach certain properties of the cor-responding risk measure are postulated which imply its decomposability. The other approach deals directly with conditional optimality of solutions of the considered problem. The aim of this paper is to discuss a relation between these two approaches.

math.OC↗

arXiv2018

On the Galerkin approximation and strong norm bounds for the stochastic Navier-Stokes equations with multiplicative noise

We investigate the convergence of the Galerkin approximation for the stochastic Navier-Stokes equations in an open bounded domain $\mathcal{O}$ with the non-slip boundary condition. We prove that \begin{equation*} \mathbb{E} \left[ \sup_{t \in [0,T]} ϕ_1(\lVert (u(t)-u^n(t)) \rVert^2_V) \right] \rightarrow 0 \end{equation*} as $n \rightarrow \infty$ for any deterministic time $T > 0$ and for a specified moment function $ϕ_1(x)$ where $u^n(t,x)$ denotes the Galerkin approximation of the solution $u(t,x)$. Also, we provide a result on uniform boundedness of the moment $\mathbb{E} [ \sup_{t \in [0,T]} ϕ(\lVert u(t) \rVert^2_V) ] $ where $ϕ$ grows as a single logarithm at infinity. Finally, we summarize results on convergence of the Galerkin approximation up to a deterministic time $T$ when the $V$-norm is replaced by the $H$-norm.

math.AP↗

arXiv2018

Robust Optimal Control Using Conditional RiskMappings in Infinite Horizon

We use one-step conditional risk mappings to formulate a risk averse version of a total cost problem on a controlled Markov process in discrete time infinite horizon. The nonnegative one step costs are assumed to be lower semi-continuous but not necessarily bounded. We derive the conditions for the existence of the optimal strategies and solve the problem explicitly by giving the robust dynamic programming equations under very mild conditions. We further give an $ε$-optimal approximation to the solution and illustrate our algorithm in two examples of optimal investment and LQ regulator problems.

math.OC↗

arXiv2015

Controlled Markov Chains with AVaR Criteria for Unbounded Costs

In this paper, we consider the control problem with the Average-Value-at-Risk (AVaR) criteria of the possibly unbounded $L^{1}$-costs in infinite horizon on a Markov Decision Process (MDP). With a suitable state aggregation and by choosing a priori a global variable $s$ heuristically, we show that there exist optimal policies for the infinite horizon problem. To our knowledge, this is the first work of deriving dynamic programming equations with $L^1$-unbounded costs via AVaR-operator.

math.PR↗

arXiv2014

On the Coherent Risk Measure Representations in the Discrete Probability Spaces

We give a complete characterization of both comonotone and not comonotone coherent risk measures in the discrete finite probability space, where each outcome is equally likely. To the best of our knowledge, this is the first work that characterizes \textit{and} distinguishes comonotone and not comonotone coherent risk measures via a simplified AVaR representation in this probability space, which is crucial in applications and simulations.

q-fin.RM↗