Nils Löhndorf

A Quasi-Newton Algorithm for Optimal Discretization of Markov Processes

  • Nils Löhndorf
  • David Wozabal
    • Categories Stochastic Programming Tags , , , , ,

    In stochastic programming and stochastic-dynamic programming discretization of random model parameters is often unavoidable. We propose a quasi-Newton learning algorithm to discretize multi-dimensional, continuous discrete-time Markov processes to scenario lattices by minimizing the Wasserstein distance between the unconditional distributions of process and lattice. Scenario lattices enable accurate discretization of the conditional distributions of Markov processes … Read more

    Optimizing Vaccine Distribution in Developing Countries under Natural Disaster Risk

  • Bonn Kleiford Seranilla
  • Nils Löhndorf
    • Categories (Mixed) Integer Linear Programming, Dynamic Programming, Stochastic Programming Tags , , ,

    For many developing countries, COVID-19 vaccination roll-out programs are not only slow but vaccination centers are also exposed to the risk of natural disaster, like flooding, which may slow down vaccination progress even further. Policy-makers in developing countries therefore seek to implement strategies that hedge against distribution risk in order for vaccination campaigns to run … Read more

    The Value of Coordination in Multi-Market Bidding of Grid Energy Storage

  • Nils Löhndorf
  • David Wozabal
    • Categories Applications - OR and Management Sciences, Stochastic Programming Tags , , , , ,

    We consider the problem of a storage owner who trades in a multi-settlement electricity market comprising an auction-based day-ahead market and a continuous intraday market. We show in a stylized model that a coordinated policy that reserves capacity for the intraday market is optimal and that the gap to a sequential policy increases with intraday … Read more

    Batch Learning in Stochastic Dual Dynamic Programming

  • Daniel Ávila
  • Nils Löhndorf
  • Anthony Papavasiliou
    • Categories Dynamic Programming, Stochastic Programming Tags , , , ,

    We consider the stochastic dual dynamic programming (SDDP) algorithm, which is a widely employed algorithm applied to multistage stochastic programming, and propose a variant using batch learning, a technique used with success in the reinforcement learning framework. We cast SDDP as a type of Q-learning algorithm and describe its application in both risk neutral and … Read more

    Modeling Time-dependent Randomness in Stochastic Dual Dynamic Programming

  • Nils Löhndorf
  • Alexander Shapiro
    • Categories Stochastic Programming Tags , , ,

    We consider the multistage stochastic programming problem where uncertainty enters the right-hand sides of the problem. Stochastic Dual Dynamic Programming (SDDP) is a popular method to solve such problems under the assumption that the random data process is stagewise independent. There exist two approaches to incorporate dependence into SDDP. One approach is to model the … Read more

    Gas Storage Valuation in Incomplete Markets

  • Nils Löhndorf
  • David Wozabal
    • Categories Applications - OR and Management Sciences, Stochastic Programming Tags , , ,

    Natural gas storage valuation is an important problem in energy trading, yet most valuation approaches are based on heuristics or ignore that gas markets are incomplete. We propose an exact valuation model for incomplete gas markets based on multistage stochastic programming. Market incompleteness structurally changes the problem of storage valuation and asset backed trading and … Read more

    An empirical analysis of scenario generation methods for stochastic optimization

  • Nils Löhndorf
    • Categories Stochastic Programming Tags , , , , , , ,

    This work presents an empirical analysis of popular scenario generation methods for stochastic optimization, including quasi-Monte Carlo, moment matching, and methods based on probability metrics, as well as a new method referred to as Voronoi cell sampling. Solution quality is assessed by measuring the error that arises from using scenarios to solve a multi-dimensional newsvendor … Read more

    Simulation Optimization for the Stochastic Economic Lot Scheduling Problem with Sequence-Dependent Setup Times

  • Nils Löhndorf
  • Stefan Minner
  • Manuel Riel
    • Categories Optimization of Simulated Systems, Scheduling, Stochastic Approaches Tags , , , , ,

    We consider the stochastic economic lot scheduling problem (SELSP) with lost sales and random demand, where switching between products is subject to sequence-dependent setup times. We propose a solution based on simulation optimization using an iterative two-step procedure which combines global policy search with local search heuristics for the traveling salesman sequencing subproblem. To optimize … Read more

    Optimizing Trading Decisions for Hydro Storage Systems using Approximate Dual Dynamic Programming

  • Nils Löhndorf
  • David Wozabal
  • Stefan Minner
    • Categories Applications - OR and Management Sciences, Dynamic Programming, Stochastic Programming Tags , , ,

    We propose a new approach to optimize operations of hydro storage systems with multiple connected reservoirs which participate in wholesale electricity markets. Our formulation integrates short-term intraday with long-term interday decisions. The intraday problem considers bidding decisions as well as storage operation during the day and is formulated as a stochastic program. The interday problem … Read more

    Simulation Optimization for the Stochastic Economic Lot Scheduling Problem

  • Nils Löhndorf
  • Stefan Minner
    • Categories Dynamic Programming, Optimization of Simulated Systems, Scheduling Tags , , , , ,

    We study simulation optimization methods for the stochastic economic lot scheduling problem. In contrast to prior research, we focus on methods that treat this problem as a black box. Based on a large-scale numerical study, we compare approximate dynamic programming with a global search for parameters of simple control policies. We propose two value function … Read more