Martin Schmidt

An Alternating Method for Cardinality-Constrained Optimization: A Computational Study for the Best Subset Selection and Sparse Portfolio Problems

  • Carina Moreira Costa
  • Dennis Kreber
  • Martin Schmidt
    • Categories (Mixed) Integer Nonlinear Programming, Finance and Economics, Statistics Tags , , , ,

    Cardinality-constrained optimization problems are notoriously hard to solve both in theory and practice. However, as famous examples such as the sparse portfolio optimization and best subset selection problems show, this class is extremely important in real-world applications. In this paper, we apply a penalty alternating direction method to these problems. The key idea is to … Read more

    On Linear Bilevel Optimization Problems with Complementarity-Constrained Lower Levels

  • Steven A. Gabriel
  • Martin Schmidt
  • Marina Leal
    • Categories Applications - OR and Management Sciences, Complementarity and Variational Inequalities Tags , , , , ,

    We consider a novel class of linear bilevel optimization models with a lower level that is a linear program with complementarity constraints (LPCC). We present different single-level reformulations depending on whether the linear complementarity problem (LCP) as part of the lower-level constraint set depends on the upper-level decisions or not as well as on whether … Read more

    Why there is no need to use a big-M in linear bilevel optimization: A computational study of two ready-to-use approaches

  • Thomas Kleinert
  • Martin Schmidt
    • Categories (Mixed) Integer Linear Programming, Complementarity and Variational Inequalities, Cutting Plane Approaches Tags , , , , ,

    Linear bilevel optimization problems have gained increasing attention both in theory as well as in practical applications of Operations Research (OR) during the last years and decades. The latter is mainly due to the ability of this class of problems to model hierarchical decision processes. However, this ability makes bilevel problems also very hard to … Read more

    Global Optimization for the Multilevel European Gas Market System with Nonlinear Flow Models on Trees

  • Lars Schewe
  • Martin Schmidt
  • Johannes Thürauf
    • Categories Applications - OR and Management Sciences, Global Optimization, Robust Optimization Tags , , , ,

    The European gas market is implemented as an entry-exit system, which aims to decouple transport and trading of gas. It has been modeled in the literature as a multilevel problem, which contains a nonlinear flow model of gas physics. Besides the multilevel structure and the nonlinear flow model, the computation of so-called technical capacities is … Read more

    Affinely Adjustable Robust Linear Complementarity Problems

  • Christian Biefel
  • Frauke Liers
  • Martin Schmidt
  • Jan Hendrik Rolfes
    • Categories (Mixed) Integer Linear Programming, Complementarity and Variational Inequalities, Robust Optimization Tags , , , ,

    Linear complementarity problems are a powerful tool for modeling many practically relevant situations such as market equilibria. They also connect many sub-areas of mathematics like game theory, optimization, and matrix theory. Despite their close relation to optimization, the protection of LCPs against uncertainties – especially in the sense of robust optimization – is still in … Read more

    A Tractable Multi-Leader Multi-Follower Peak-Load-Pricing Model with Strategic Interaction

  • Veronika Grimm
  • Lars Schewe
  • Martin Schmidt
  • Daniel Nowak
  • Alexandra Schwartz
  • Gregor Zöttl
    • Categories Applications - OR and Management Sciences, Game Theory, Global Optimization Tags , , ,

    While single-level Nash equilibrium problems are quite well understood nowadays, less is known about multi-leader multi-follower games. However, these have important applications, e.g., in the analysis of electricity and gas markets, where often a limited number of firms interacts on various subsequent markets. In this paper, we consider a special class of two-level multi-leader multi-follower … Read more

    Complementarity Modeling of a Ramsey-Type Equilibrium Problem with Heterogeneous Agents

  • Leonhard Frerick
  • Martin Schmidt
  • Georg Müller-Fürstenberger
  • Max Späth
    • Categories Complementarity and Variational Inequalities, Finance and Economics Tags , , ,

    We contribute to the field of Ramsey-type equilibrium models with heterogeneous agents. To this end, we state such a model in a time-continuous and time-discrete form, which in the latter case leads to a finite-dimensional mixed complementarity problem. We prove the existence of solutions of the latter problem using the theory of variational inequalities and … Read more

    The Cost of Decoupling Trade and Transport in the European Entry-Exit Gas Market with Linear Physics Modeling

  • Tom Böttger
  • Veronika Grimm
  • Thomas Kleinert
  • Martin Schmidt
    • Categories (Mixed) Integer Nonlinear Programming, Applications - OR and Management Sciences, Robust Optimization Tags , , ,

    Liberalized gas markets in Europe are organized as entry-exit regimes so that gas trade and transport are decoupled. The decoupling is achieved via the announcement of technical capacities by the transmission system operator (TSO) at all entry and exit points of the network. These capacities can be booked by gas suppliers and customers in long-term … Read more

    Closing the Gap in Linear Bilevel Optimization: A New Valid Primal-Dual Inequality

  • Thomas Kleinert
  • Martine Labbé
  • Martin Schmidt
  • Fränk Plein
    • Categories (Mixed) Integer Linear Programming, Complementarity and Variational Inequalities, Cutting Plane Approaches Tags , , ,

    Linear bilevel optimization problems are often tackled by replacing the linear lower-level problem with its Karush–Kuhn–Tucker (KKT) conditions. The resulting single-level problem can be solved in a branch-and-bound fashion by branching on the complementarity constraints of the lower-level problem’s optimality conditions. While in mixed-integer single-level optimization branch- and-cut has proven to be a powerful extension … Read more

    Robustification of the k-Means Clustering Problem and Tailored Decomposition Methods: When More Conservative Means More Accurate

  • Jan Pablo Burgard
  • Carina Moreira Costa
  • Martin Schmidt
    • Categories (Mixed) Integer Nonlinear Programming, Robust Optimization Tags , , , ,

    k-means clustering is a classic method of unsupervised learning with the aim of partitioning a given number of measurements into k clusters. In many modern applications, however, this approach suffers from unstructured measurement errors because the k-means clustering result then represents a clustering of the erroneous measurements instead of retrieving the true underlying clustering structure. … Read more