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DTSTART;TZID=Europe/Berlin:20250120T160000
DTEND;TZID=Europe/Berlin:20250120T170000
DTSTAMP:20250106T121301Z
CREATED:20250106T121301Z
LAST-MODIFIED:20250106T121301Z
UID:7671-1737388800-1737392400@alop.uni-trier.de
SUMMARY:ALOP Colloquium with Sonja Steffensen
DESCRIPTION:On Monday\, January 20\, 2025 at 16:00 c.t. Dr. Sonja Steffensen\, RWTH Aachen\, will speak at the ALOP Colloquium about her recent work. \n  \nRelaxation Approaches for Nonlinear Sparse Optimization Problems \nAbstract: \nIn many applications\, sparse solutions are favoured over non-sparse solutions with comparable objective value\, as for example in statistical and deep learning applications. One approach to induce sparsity relies on the l_0 norm as an additional term in the objective. Often this semicontinuous function is approximated using the continuous and convex l_1-norm as a surrogate function instead. However\, this can lead to suboptimal results with respect to the sparsity properties of the solution. \nIn this talk\, we will present an alternative exact reformulation (with respect to the l_0 norm)  using non-smooth nonlinear functions to formulate the minimization of the number of non-zero entries. The resulting problem is similar (but not equivalent) to the class of mathematical programs with complementarity constraints (MPCC). As for MPCCs relaxing the problem to a standard nonlinear program we can then apply a general nonlinear solver. In our talk we will discuss and relate the relations between the different reformulations in particular with respect to the original problem. Furthermore\, we accompany the theoretical results by some numerical tests using randomly generated data sets. \n  \nPlease join us at 16:00 c.t. in HS 9.
URL:https://alop.uni-trier.de/event/alop-colloquium-with-sonja-steffensen/
LOCATION:Trier University\, E Building\, Universitätsring 15\, Trier\, Germany
CATEGORIES:Colloquium
ORGANIZER;CN="RTG ALOP at Trier University":MAILTO:ALOP@uni-trier.de
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Berlin:20241216T160000
DTEND;TZID=Europe/Berlin:20241216T170000
DTSTAMP:20241112T115510Z
CREATED:20241112T115510Z
LAST-MODIFIED:20241112T115510Z
UID:7632-1734364800-1734368400@alop.uni-trier.de
SUMMARY:ALOP Colloquium with Christina Schenk
DESCRIPTION:On Monday\, December 16\, 2024 at 16:00 c.t. Dr. Christina Schenk\, IMDEA Materials Insitute\, Getafe (Madrid)\, will speak at the ALOP Colloquium about her recent work. \n  \nMixed-dimensional Linked Models and Reinforcement Learning-Based Control of Reaction-Diffusion Problems \nAbstract: \nIn Mathematical modeling is a powerful tool for tackling complex challenges across various fields. For instance\, during the SARS-CoV-2 pandemic\, modeling spatial dynamics and high-diffusion pathways\, such as airways and highways\, proved essential for effective decision-making in managing the crisis. \nIn this talk\, we present two approaches to enhance modeling and decision-making. We start with linking models of different dimensionalities to represent a single physical phenomenon\, specifically coupling two diffusive models—one over a continuum and another over a curve—resulting in a mixed-dimensional problem. We establish the unconditional stability and convergence of both continuous and discrete linked models using mixed finite elements. Supported by numerical examples\, we demonstrate the benefits of combining these models and show how our methods can infer solutions from incomplete data. \nBuilding on these results\, we explore the application of reinforcement learning (RL) to automatic control problems in thermal and disease transport. We adapt a stochastic policy gradient algorithm and propose novel reward functions to guide the RL agent in interacting with a reaction-diffusion model. Our approach successfully implements control strategies despite necessary model simplifications\, showcasing the potential of RL to solve complex control problems. \nBy combining theoretical and numerical insights from mixed-dimensional modeling and machine learning\, this talk highlights new results for advancing diffusive modeling and data-driven control strategies\, opening new avenues for research in data science and control applications. \n  \nThis is joint work with Aditya Vasudevan\, David Portillo (UPM)\, Ignacio Romero\, and Maciej Haranczyk. \n  \nPlease join us at 16:00 c.t. in HS 9.
URL:https://alop.uni-trier.de/event/alop-colloquium-with-christina-schenk/
LOCATION:Trier University\, E Building\, Universitätsring 15\, Trier\, Germany
CATEGORIES:Colloquium
ORGANIZER;CN="RTG ALOP at Trier University":MAILTO:ALOP@uni-trier.de
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Berlin:20240212T160000
DTEND;TZID=Europe/Berlin:20240212T170000
DTSTAMP:20231221T143522Z
CREATED:20231221T094533Z
LAST-MODIFIED:20231221T143522Z
UID:7334-1707753600-1707757200@alop.uni-trier.de
SUMMARY:ALOP Colloquium with Dorothee Henke
DESCRIPTION:On Monday\, February 12\, 2024 at 16:00 c.t. Dorothee Henke\, University of Passau\, will speak at the ALOP Colloquium about her recent work: \n  \nOn the Complexity of the Bilevel Shortest Path Problem \nAbstract: \nWe introduce a new bilevel version of the classical shortest path problem and completely characterize its computational complexity with respect to several problem variants. In our problem\, the leader and the follower each control a subset of the edges of a graph and together aim at building a path between two given vertices\, while each of the two players minimizes the length of the resulting path according to their own edge lengths. We investigate both directed and undirected graphs\, as well as the special case of acyclic directed graphs. Moreover\, we distinguish two versions of the follower’s problem: Either he has to complete the edge set selected by the leader such that the joint solution is exactly a path\, without any additional edges\, or he is allowed to include only a subset of the leader’s selection into the final path. In general\, the bilevel problem turns out to be much harder in the former case: We show that the follower’s problem is already NP-hard here and the leader’s problem is even hard for the second level of the polynomial hierarchy\, while both problems are one level easier in the latter case. Interestingly\, for acyclic directed graphs\, this difference turns around\, as we give a polynomial-time algorithm for the first version of the bilevel problem\, but it stays NP-hard in the second case. \nThis is joint work with Lasse Wulf. \n  \nPlease join us at 16:00 c.t. in HS 9.
URL:https://alop.uni-trier.de/event/alop-colloquium-with-dorothee-henke/
LOCATION:Trier University\, E Building\, Universitätsring 15\, Trier\, Germany
CATEGORIES:Colloquium
ORGANIZER;CN="RTG ALOP at Trier University":MAILTO:ALOP@uni-trier.de
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Berlin:20231211T160000
DTEND;TZID=Europe/Berlin:20231211T170000
DTSTAMP:20230906T085744Z
CREATED:20230814T123248Z
LAST-MODIFIED:20230906T085744Z
UID:7277-1702310400-1702314000@alop.uni-trier.de
SUMMARY:ALOP Colloquium with Mathias Staudigl
DESCRIPTION:On Monday\, December 11\, 2023 at 16:00 c.t. Prof. Dr. Mathias Staudigl\, University of Mannheim\, will speak at the ALOP Colloquium about his recent work: \n  \nA regularized variance-reduced modified extragradient method for stochastic hierarchical games \nAbstract:\n \nThe theory of learning in games has so far focused mainly on games with simultaneous moves. Recently\, researchers in machine learning have started investigating learning dynamics in games involving hierarchical decision-making. We consider an N-player hierarchical game in which the ith player’s objective comprises of an expectation-valued term\, parametrized by rival decisions\, and a hierarchical term. Such a framework allows for capturing a broad range of stochastic hierarchical optimization problems\, Stackelberg equilibrium problems\, and leader-follower games. We develop an iteratively regularized and smoothed variance-reduced modified extragradient framework for learning hierarchical equilibria in a stochastic setting. We equip our analysis with rate statements\, complexity guarantees\, and almost-sure convergence claims. We then extend these statements to settings where the lower-level problem is solved inexactly and provide the corresponding rate and complexity statements. \n  \nPlease join us at 16:00 c.t. in HS 9.
URL:https://alop.uni-trier.de/event/alop-colloquium-with-mathias-staudigl/
LOCATION:Trier University\, E Building\, Universitätsring 15\, Trier\, Germany
CATEGORIES:Colloquium
ORGANIZER;CN="RTG ALOP at Trier University":MAILTO:ALOP@uni-trier.de
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Berlin:20231204T160000
DTEND;TZID=Europe/Berlin:20231204T170000
DTSTAMP:20231024T083813Z
CREATED:20230814T123308Z
LAST-MODIFIED:20231024T083813Z
UID:7275-1701705600-1701709200@alop.uni-trier.de
SUMMARY:ALOP Colloquium with Marc Pfetsch
DESCRIPTION:On Monday\, December 4\, 2023 at 16:00 c.t. Prof. Dr. Marc Pfetsch\, TU Darmstadt\, will speak at the ALOP Colloquium about his recent work: \n  \nCombinatorial Aspects of Physical Networks \nAbstract:\n \nThis talk considers combinatorial properties of physical networks like water\, gas\, heat\, and electrical networks. One common model are potential-based flows\, for which\, in general\, the corresponding flows depend in a nonlinear way on potentials (e.g.\, pressures) and are unique. The talk will discuss two different topics. The first is how the fact that flows in physical networks are acyclic can be used to strengthen mixed-integer optimization formulations and to derive combinatorial models. The second concerns the recovery of the structure of the network\, given only information at the entries and exits. The talk will demonstrate positive and negative results in this direction. \n  \nPlease join us at 16:00 c.t. in HS 9.
URL:https://alop.uni-trier.de/event/alop-colloquium-with-marc-pfetsch/
LOCATION:Trier University\, E Building\, Universitätsring 15\, Trier\, Germany
CATEGORIES:Colloquium
ORGANIZER;CN="RTG ALOP at Trier University":MAILTO:ALOP@uni-trier.de
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Berlin:20230717T160000
DTEND;TZID=Europe/Berlin:20230717T170000
DTSTAMP:20230704T090825Z
CREATED:20230704T090825Z
LAST-MODIFIED:20230704T090825Z
UID:7238-1689609600-1689613200@alop.uni-trier.de
SUMMARY:ALOP Colloquium with Gabriele Dragotto
DESCRIPTION:On Monday\, July 17\, 2023 at 16:00 c.t. Dr. Gabriele Dragotto\, Princeton University\, will speak at the ALOP Colloquium about his recent work: \n  \nLearn-and-Play: Data\, Agents\, and Interactions \nAbstract: \nHow should an energy company determine its optimal production schedule? How should transport authorities design transportation networks? How should graduate students from medical schools be matched with residency training? In all these contexts\, decision-making is rarely an individual task; on the contrary\, it often involves the mutual interaction of several self-interested decision-makers deciding by solving optimization problems. However\, the agents’ self-driven behavior often conflicts with the greater societal goals; in such cases\, external regulators (e.g.\, governments) can intervene in the agents’ interaction via incentives\, laws\, and regulations. This talk provides a method for learning the agents’ preferences from data to design prescriptive interventions that possibly improve social welfare.  \n  \nPlease join us at 16:00 c.t. in HS 10.
URL:https://alop.uni-trier.de/event/alop-colloquium-with-gabriele-dragotto/
LOCATION:Trier University\, E Building\, Universitätsring 15\, Trier\, Germany
CATEGORIES:Colloquium
ORGANIZER;CN="RTG ALOP at Trier University":MAILTO:ALOP@uni-trier.de
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Berlin:20230626T160000
DTEND;TZID=Europe/Berlin:20230626T170000
DTSTAMP:20230620T065239Z
CREATED:20230102T140258Z
LAST-MODIFIED:20230620T065239Z
UID:6983-1687795200-1687798800@alop.uni-trier.de
SUMMARY:ALOP Colloquium with Alexander Martin
DESCRIPTION:On Monday\, June 26\, 2023 at 16:00 c.t. Prof. Dr. Alexander Martin\, Fraunhofer IIS; Technische Universität Nürnberg \, will speak at the ALOP Colloquium about his recent work: \n  \nMixed Integer Optimization Problems on Networks with PDE Constraints \nAbstract: \nMotivated by challenging questions in the transformation and control of our energy system we study mixed integer optimization problems on networks with PDE constraints. Control decisions are typically modeled by integer optimization methods\, while the physical behavior of water\, gas and hydrogen is represented in a continuous nonlinear way\, e.g. by partial differential equations (PDEs). \nThe topic of this talk is to discuss mathematical approaches and insights for the efficient coupling of integer and continuous nonlinear optimization in this context. \nWe will also demonstrate the numerical success using examples from gas network optimization within the framework of the SFB/TR 154. \n  \nPlease join us at 16:00 c.t. in HS 10. \n  \n 
URL:https://alop.uni-trier.de/event/alop-colloquium-with-alexander-martin/
LOCATION:Trier University\, E Building\, Universitätsring 15\, Trier\, Germany
CATEGORIES:Colloquium
ORGANIZER;CN="RTG ALOP at Trier University":MAILTO:ALOP@uni-trier.de
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Berlin:20230515T160000
DTEND;TZID=Europe/Berlin:20230515T170000
DTSTAMP:20230509T105746Z
CREATED:20230102T135859Z
LAST-MODIFIED:20230509T105746Z
UID:6981-1684166400-1684170000@alop.uni-trier.de
SUMMARY:ALOP Colloquium with Marc Steinbach
DESCRIPTION:On Monday\, May 15\, 2023 at 16:45 c.t. Prof. Dr. Marc Steinbach\, Leibniz Universität Hannover\, will speak at the ALOP Colloquium about his recent work: \n  \nNLP Models for Generating Synthetic Vascular Trees \nAbstract: \nWe introduce a new framework for generating synthetic vascular trees based on NLP models for optimizing the local and global tree geometry. A second novelty is a metaheuristic optimization step for the tree topology. \nThe talk discusses these optimization models and compares the new algorithm to the standard CCO approach for generating vascular trees. Moreover\, it compares the influence of different model variants on trees with 14 branching levels and roughly two million nodes. \nThe validation against a corrosion cast of a human liver shows that the trees generated by our new framework match the physiological data better than those generated by the standard CCO approach. \n  \nPlease join us at 16:45 c.t. in HS 10. \n 
URL:https://alop.uni-trier.de/event/alop-colloquium-with-marc-steinbach/
LOCATION:Trier University\, E Building\, Universitätsring 15\, Trier\, Germany
CATEGORIES:Colloquium
ORGANIZER;CN="RTG ALOP at Trier University":MAILTO:ALOP@uni-trier.de
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Berlin:20230424T160000
DTEND;TZID=Europe/Berlin:20230424T170000
DTSTAMP:20230329T140042Z
CREATED:20230102T135641Z
LAST-MODIFIED:20230329T140042Z
UID:6979-1682352000-1682355600@alop.uni-trier.de
SUMMARY:ALOP Colloquium with René Henrion
DESCRIPTION:On Monday\, April 24\, 2023 at 16:00 c.t. Dr. René Henrion\, WIAS Berlin\, will speak at the ALOP Colloquium about his recent work: \n  \nAbstract: \nChance constraints are widely used in stochastic programming when inequality constraints in an optimization problem are affected by some random parameter. A chance constraint then defines a decision to be feasible whenever the constraint is satisfied at some specified probability. \nOriginally developed in the framework of operations research\, chance constraints attract increasing attention also in risk averse optimal control problems. \nThe talk addresses various aspects of chance constraints related with applications\, numerics and optimality conditions in PDE-constrained optimization. \n  \nPlease join us at 16:00 c.t. in HS 10.
URL:https://alop.uni-trier.de/event/alop-colloquium-with-rene-henrion/
LOCATION:Trier University\, E Building\, Universitätsring 15\, Trier\, Germany
CATEGORIES:Colloquium
ORGANIZER;CN="RTG ALOP at Trier University":MAILTO:ALOP@uni-trier.de
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Berlin:20230213T160000
DTEND;TZID=Europe/Berlin:20230213T170000
DTSTAMP:20230202T125328Z
CREATED:20221129T151056Z
LAST-MODIFIED:20230202T125328Z
UID:6897-1676304000-1676307600@alop.uni-trier.de
SUMMARY:ALOP Colloquium with Marc Goerigk
DESCRIPTION:On Monday\, February 13\, 2023 at 16:00 c.t. Prof. Dr. Marc Goerigk\, University of Siegen\, will speak at the ALOP Colloquium about his recent work: \n  \nModels for Interpretable Optimization \nAbstract: \nWhile explainability and interpretability has become a major research area in machine learning over the past years\, in operations research and mathematical programming the comprehensibility of solutions is hardly every scrutinized. Likely due to the existence of explicitly stated models and well defined solution processes\, experts have high confidence in the correctness and usefulness of found solutions. However\, even understanding a mathematical model can quickly become a challenging task\, especially for people not familiar with modeling techniques. Users with less mathematical and computer background\, e.g. the planner using the optimization software and the workers in charge of implementing the result\, may consider the solver a black box. We present and experimentally validate a modeling framework that inherently provides an interpretable decision rule\, trying to clarify the causal effect of occurring scenario and selected solution. By restricting the number of eligible solutions and providing an interpretable rule\, e.g. in form of a decision tree\, we shift the focus towards comprehensibility and transparency. Our experiments indicate that the costs of interpretability can be small\, i.e.\, only a small percentage of nominal performance needs to be sacrificed. \n  \nPlease join us at 16:00 c.t. in HS 9. \n 
URL:https://alop.uni-trier.de/event/alop-colloquium-with-marc-goerigk/
LOCATION:Trier University\, E Building\, Universitätsring 15\, Trier\, Germany
CATEGORIES:Colloquium
ORGANIZER;CN="RTG ALOP at Trier University":MAILTO:ALOP@uni-trier.de
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Berlin:20230206T164500
DTEND;TZID=Europe/Berlin:20230206T174500
DTSTAMP:20230126T125829Z
CREATED:20221130T082641Z
LAST-MODIFIED:20230126T125829Z
UID:6913-1675701900-1675705500@alop.uni-trier.de
SUMMARY:ALOP Colloquium with Hanno Gottschalk
DESCRIPTION:On Monday\, February 6 2023 at 16:00 c.t. Prof. Dr. Hanno Gottschalk\, University of Wuppertal\, will speak at the ALOP Colloquium about his recent work: \n  \nTheory and Applications of Generative Adversarial Learning \nAbstract: \nGenerative learning is the machine learning task of learning to synthesize new examples that assimilate a given distribution. Since the introduction of generative adversarial networks in the year 2014\, generative learning underwent a rapid development and reached a considerable technological level. \nIn this talk\, generative adversarial learning is studied from a mathematical point of view. However\, we also give applications on domain transfer and sampling from the invariant measure of ergodic processes. \n  \nPlease join us at 16:45 c.t. in HS 10.
URL:https://alop.uni-trier.de/event/alop-colloquium-with-prof-dr-hanno-gottschalk-2/
LOCATION:Trier University\, E Building\, Universitätsring 15\, Trier\, Germany
CATEGORIES:Colloquium
ORGANIZER;CN="RTG ALOP at Trier University":MAILTO:ALOP@uni-trier.de
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Berlin:20230130T160000
DTEND;TZID=Europe/Berlin:20230130T170000
DTSTAMP:20230124T080128Z
CREATED:20230116T141030Z
LAST-MODIFIED:20230124T080128Z
UID:6991-1675094400-1675098000@alop.uni-trier.de
SUMMARY:CANCELED - ALOP Colloquium with Mark Vogelsberger
DESCRIPTION:Unfortunately\, the talk has to be rescheduled. \nAs soon as there is a new date\, we will announce it here.
URL:https://alop.uni-trier.de/event/alop-colloquium-with-mark-vogelsberger/
CATEGORIES:Colloquium
ORGANIZER;CN="RTG ALOP at Trier University":MAILTO:ALOP@uni-trier.de
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Berlin:20230123T160000
DTEND;TZID=Europe/Berlin:20230123T170000
DTSTAMP:20221216T110910Z
CREATED:20221130T084745Z
LAST-MODIFIED:20221216T110910Z
UID:6893-1674489600-1674493200@alop.uni-trier.de
SUMMARY:ALOP Colloquium with Jannis Kurtz
DESCRIPTION:On Monday\, January 23\, 2023 at 16:00 c.t. Dr. Jannis Kurtz\, University of Amsterdam\, will speak at the ALOP Colloquium about his recent work: \n  \nDeriving Robust Counterfactual Explanations for Machine Learning Models via Two-Stage Robust Optimization \nAbstract: \nNowadays machine learning models are often used to make decisions based on personal data which significantly affect individuals\, e.g. the decision of granting a loan to a person or not. However many machine learning models behave like black-boxes and can incorporate biases contained in the data into their decision which is why in 2016 the European Union enacted the “right to explanation”.   \nCounterfactual explanations (CE) play an important role in providing such explanations and hence improving explainability. The idea is to find the smallest changes which have to be made to a data point such that the model would have changed its decision. Unfortunately most of the common methods can only provide one CE which can be unrealistic to reach for the user. \nIn this work we present a model to calculate robust CEs\, i.e. CEs where after changing each attribute in a certain range the perturbed data point still remains a CE. Hence our method provides a whole set of CEs and the user can choose the one which is most reasonable. We use algorithmic ideas from two-stage robust optimization to calculate robust CEs for the most popular ML methods including logistic regression\, decision trees and neural networks. We show that our method is able to calculate CEs efficiently for common data sets. \n  \nPlease join us at 16:00 c.t. in HS 9. \n 
URL:https://alop.uni-trier.de/event/alop-colloquium-with-jannis-kurtz/
LOCATION:Trier University E Building\, Universitätsring 15\, Trier\, 54296\, Germany
CATEGORIES:Colloquium
ORGANIZER;CN="RTG ALOP at Trier University":MAILTO:ALOP@uni-trier.de
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Berlin:20221128T160000
DTEND;TZID=Europe/Berlin:20221128T170000
DTSTAMP:20221216T110700Z
CREATED:20221025T102708Z
LAST-MODIFIED:20221216T110700Z
UID:6801-1669651200-1669654800@alop.uni-trier.de
SUMMARY:ALOP Colloquium with Martina Cerulli
DESCRIPTION:On Monday\, November 28 2022 at 16:00 c.t. Martina Cerulli\, ESSEC Business School of Paris\, will speak at the ALOP Colloquium about her recent work: \n  \nOn the dualization of the inner problems of Semi-Infinite programs \nAbstract: \nIn this talk\, we will discuss a solution approach for Semi-Infinite programs (SIPs) based on the dualization of the inner problem\, i.e.\, the problem of finding the constraint that is the most violated by a given point. After a brief introduction to SIPs and the classical solution techniques for these optimization programs\, we will consider two practical problems that can be modeled as SIPs: the aircraft conflict resolution and the collapsed k-core problem. Then\, we will present the results of the paper “Convergent algorithms for a class of convex semi-infinite programs” by M. Cerulli\, A. Oustry\, C. D’Ambrosio\, L. Liberti\, accepted for publication on SIAM Journal on Optimization. In this paper\, we focus on convex SIPs with an infinite number of quadratically parametrized constraints\, not necessarily convex w.r.t. the parameter. A new convergent approach to solve these SIPs is proposed\, leveraging the dualization technique. Based on the Lagrangian dual of the inner problem\, a convex and tractable restriction of the considered SIP is derived. We state sufficient conditions for the optimality of this restriction. If these conditions are not met\, the restriction is enlarged through an Inner-Outer Approximation Algorithm\, and its value converges to the value of the original semi-infinite problem. This new algorithmic approach is compared with the classical Cutting Plane algorithm. We propose a new rate of convergence of the Cutting Plane algorithm\, directly related to the iteration index\, derived when the objective function is strongly convex\, and under a strict feasibility assumption. We successfully test the two methods on two applications: the constrained quadratic regression and a zero-sum game with cubic payoff.  \nPlease join us at 16:00 c.t. in HS 9.
URL:https://alop.uni-trier.de/event/alop-colloquium-with-martina-cerulli/
LOCATION:Trier University E Building\, Universitätsring 15\, Trier\, 54296\, Germany
CATEGORIES:Colloquium
ORGANIZER;CN="RTG ALOP at Trier University":MAILTO:ALOP@uni-trier.de
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Berlin:20220804T160000
DTEND;TZID=Europe/Berlin:20220804T170000
DTSTAMP:20220721T081156Z
CREATED:20220718T130428Z
LAST-MODIFIED:20220721T081156Z
UID:6654-1659628800-1659632400@alop.uni-trier.de
SUMMARY:ALOP Colloquium with Kendra Reiter
DESCRIPTION:On Thursday\, August 4 2022 at 16:00 c.t. Kendra Reiter\, MTU Maintenance (Hannover)\, will speak at the ALOP Colloquium about her recent work: \n  \nBuilding a geo-referenced microsimulation model with discrete optimization* \n*joint work with Dr. Ulf Friedrich\, OVGU Magdeburg and Prof. Dr. Ralf Münnich\, Trier University \nAbstract: \nMicrosimulation is an important tool to support evidence-based policies. To produce a fully geo-coded dataset\, where information is generally available on aggregate levels of different hierarchies\, micro units (households and persons) have to be placed into geo-coded dwellings. The microsimulation model involves mathematical optimization problems with integrality constraints on some of the optimization variables. It is therefore necessary to employ combinatorial optimization techniques to handle these discrete structures efficiently. More specifically\, fast algorithms for the sub-problem of address selection are needed: Given a population generated in the first step of the microsimulation process and a target region\, the households in the population have to be assigned to actual addresses within the region\, i.e.\, an address has to be selected for each household in the population. \nWhile the computation time is often not crucial when considering only a subset of the population\, e.g.\, for the simulation of a certain region or city\, the big-data setting of a complete model typically requires specialized\, fast algorithms and techniques from data science. For example\, in the address selection model for Germany more than 40 million households are assigned to over 25 million addresses while using several statistical variables to measure the quality of the assignment. General purpose heuristics such as simulated annealing do generally not solve this instance within an acceptable time limit and do not provide quality certificates. In addition\, large data sets from several sources (e.g.\, Open Street Map\, city registers\, grid-based census data) have to be combined and pre-processed in an efficient and secure way. \nPlease join us at 16:00 c.t. in HS 9.
URL:https://alop.uni-trier.de/event/alop-colloquium-with-ulf-friedrich-and-kendra-reiter/
LOCATION:Trier University E Building\, Universitätsring 15\, Trier\, 54296\, Germany
CATEGORIES:Colloquium
ORGANIZER;CN="RTG ALOP at Trier University":MAILTO:ALOP@uni-trier.de
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Berlin:20220613T160000
DTEND;TZID=Europe/Berlin:20220613T170000
DTSTAMP:20220608T143440Z
CREATED:20220608T101314Z
LAST-MODIFIED:20220608T143440Z
UID:6548-1655136000-1655139600@alop.uni-trier.de
SUMMARY:ALOP Colloquium with Paul Swoboda
DESCRIPTION:On Monday\, June 13\, 2022\, at 16.00 c.t. Dr. Paul Swoboda\, Max-Planck-Institut für Informatik\, Saarland Informatics Campus will present his recent work titled \nSolving 0-1 ILPs with Binary Decision Diagrams \nAbstract: \nWe present a Lagrange decomposition method for solving 0–1 integer linear programs occurring in structured prediction. We propose a sequential and a massively min-marginal averaging schemes for solving the Lagrangean dual and a perturbation technique for decoding primal solutions. For representing subproblems we use binary decision diagrams (BDDs)\, which support efficient computation of subproblem solutions and update steps. We present experimental results on combinatorial problems from MAP inference for Markov Random Fields\, quadratic assignment and cell tracking for developmental biology. Our highly parallel GPU implementation improves comes close to or outperform some state-of-the-art specialized heuristics while being problem agnostic. We additionally showcase improvement that can be obtained by integrating machine learning into our solver. \n  \nThe presentation will take place in HS 9.  Please join us for coffee in E 10 at 15:45.
URL:https://alop.uni-trier.de/event/alop-colloquium-with-paul-swoboda/
LOCATION:Trier University E Building\, Universitätsring 15\, Trier\, 54296\, Germany
CATEGORIES:Colloquium
ORGANIZER;CN="RTG ALOP at Trier University":MAILTO:ALOP@uni-trier.de
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Berlin:20220411T160000
DTEND;TZID=Europe/Berlin:20220411T170000
DTSTAMP:20220301T152303Z
CREATED:20220228T102256Z
LAST-MODIFIED:20220301T152303Z
UID:6344-1649692800-1649696400@alop.uni-trier.de
SUMMARY:ALOP-Colloquium with Dr. Akhil Vohra\, University of Cambridge
DESCRIPTION:On Monday\, April 11\, 2022\, at 16:00 c.t.\, Dr. Akhil Vohra\, University of Cambridge will speak on the topic of Bayesian Persuasion: Reduced Form Approach. \nAbstract: \nWe illustrate the usefulness of reduced form representations of Bayesian persuasion problems with two applications. In one\, the reduced form representation yields a simple algorithm to determine the support of the optimal solution. In the second\, the reduced form leads to a simple greedy algorithm to determine the maximum value a sender can achieve in any cheap talk equilibrium. \nThis presentation will take place in HS 9.  Please join us for coffee and an informal meeting with the lecturer prior to the presentation in E 10 at 15:45.
URL:https://alop.uni-trier.de/event/alop-colloquium-with-dr-akhil-vohra-university-of-cambridge/
LOCATION:Trier University\, E Building\, Universitätsring 15\, Trier\, Germany
CATEGORIES:Colloquium
ORGANIZER;CN="RTG ALOP at Trier University":MAILTO:ALOP@uni-trier.de
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Berlin:20220207T160000
DTEND;TZID=Europe/Berlin:20220207T170000
DTSTAMP:20220110T113307Z
CREATED:20211102T120107Z
LAST-MODIFIED:20220110T113307Z
UID:6260-1644249600-1644253200@alop.uni-trier.de
SUMMARY:ALOP-Colloquium with Prof. Geunyeong Byeon\, Arizona State University
DESCRIPTION:On Monday\, February 7\, 2022\, at 16:00 c.t.\, Prof. Geunyeong Byeon\, Arizona State University will speak about her recent work. \nDecomposition Methods for Bilevel Problems with Convex Follower \nAbstract: Bilevel optimization formulates hierarchical decision-making processes that arise in many real-world applications such as in pricing\, network design\, and infrastructure defense planning. This work considers a class of bilevel optimization problems where the upper level problem features some integer variables while the lower level problem enjoys strong duality. We propose a dedicated Benders decomposition method for solving this class of bilevel problems\, which decomposes the Benders subproblem into two more tractable\, sequentially solvable problems that can be interpreted as the upper and the lower level problems. We show that the Benders subproblem decomposition carries over to an interesting extension of bilevel problems\, which connects the upper level solution with the lower level dual solution\, and discuss some special cases of bilevel problems that allow sequence-independent subproblem decomposition. Several novel schemes for generating numerically stable cuts\, finding a good incumbent solution\, and accelerating the search tree are discussed. A computational study demonstrates the computational benefits of the proposed method over a state-of-the-art bilevel-tailored branch-and-cut method\, a commercial solver\, and the standard Benders method on standard test cases and the motivating applications in sequential energy markets. \nThis presentation will take place via ZOOM. A link will be e-mailed prior to the event
URL:https://alop.uni-trier.de/event/alop-colloquium-with-prof-geunyeong-byeon-arizona-state-university/
CATEGORIES:Colloquium
ORGANIZER;CN="RTG ALOP at Trier University":MAILTO:ALOP@uni-trier.de
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Berlin:20220110T160000
DTEND;TZID=Europe/Berlin:20220110T170000
DTSTAMP:20211130T112128Z
CREATED:20211117T073819Z
LAST-MODIFIED:20211130T112128Z
UID:6266-1641830400-1641834000@alop.uni-trier.de
SUMMARY:ALOP-Colloquium with Prof. Samuel Amstutz\, CMAP - Ecole Polytechnique
DESCRIPTION:On Monday\, January 10\, 2022\, at 16:00 c.t.\, Prof. Samuel Amstutz of CMAP – Ecole Polytechnique will speak about his recent work regarding  \nTopology optimization and optimal partitioning with non-local perimeter approximation \n\nTopology optimization deals with the optimal design of shapes of unknown topology. For such problems\, the perimeter may be considered as penalization to regularize the boundaries and ultimately favor the existence of optimal shapes\, but it is difficult to handle directly within algorithms because it is highly sensitive to topology changes. A classical remedy is to use approximate versions of the perimeter in the sense of Gamma-convergence. In this talk\, after reviewing the context\, I will present a (relative or total) perimeter approximation which is built upon the solution of an elliptic boundary value problem. I will discuss the advantages and drawbacks of this approach compared with alternative functionals\, and show in particular how the variational formulation of the boundary value problem can be exploited to design alternating minimizations schemes. Then I will explain how those results and methods\, through combinatorial and convex analysis techniques\, can be adapted to multiphase optimal partitioning problems with an energy term consisting of a weighted sum of Hausdorff measures of interfaces. Problems of image classification and of hydrostatics with surface tensions will be shown as examples. If time allows\, I will also discuss anisotropic variants. \n  \nThis presentation will take place via ZOOM. A link will be e-mailed prior to the event.
URL:https://alop.uni-trier.de/event/alop-colloquium-with-samuel-amstutz-cmap-ecole-polytechnique/
CATEGORIES:Colloquium
ORGANIZER;CN="RTG ALOP at Trier University":MAILTO:ALOP@uni-trier.de
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Berlin:20211115T160000
DTEND;TZID=Europe/Berlin:20211115T170000
DTSTAMP:20210521T050924Z
CREATED:20210519T085624Z
LAST-MODIFIED:20210521T050924Z
UID:5608-1636992000-1636995600@alop.uni-trier.de
SUMMARY:ALOP-Colloquium with Sungho Shin\, University of Wisconsin-Madison
DESCRIPTION:On Monday\, November 15\, 2021\, at 16:00 c.t.\, Ph.D. candidate Sungho Shin\, University of Madison-Wisonsin will speak about his recent work: \n  \nTitle: Graph-Structured Nonlinear Programming: Properties and Algorithms \n  \nA graph-structured nonlinear program (NLP) is a nonlinear optimization problem whose algebraic structure is induced by a graph. These problems arise in diverse applications such as dynamic optimization (model predictive control and moving horizon estimation)\, network optimization (energy systems and supply chain)\, optimization with embedded discretized partial differential equations\, and multi-stage stochastic programming. Building upon the existing NLP sensitivity theory\, we show that the nodal solution sensitivity against parametric perturbation decays exponentially with respect to the distance from the perturbation point. Remarkably\, this result (which we call exponential decay of sensitivity; EDS) holds under fairly standard regularity assumptions used in classical NLP sensitivity theory: second-order sufficiency conditions and the linear independence constraint qualification. EDS allows the creation of novel computing strategies\, the overlapping Schwarz decomposition method (also known as domain decomposition). This method decomposes a graph-structured NLP into multiple smaller subproblems over overlapping subdomains and solves the subproblems in parallel and iteratively with the exchange of information at boundries. Based on the EDS result\, we prove that for a certain class of problems satisfying the regularity assumptions\, the convergence rate of the overlapping Schwarz method improves exponentially with the size of overlap; thus\, overlap accelerates the convergence. With real-world case studies on gas and electric networks\, we demonstrate the effectiveness of the overlapping Schwarz method. \n  \nThis presentation will take place via ZOOM. A link will be e-mailed prior to the event
URL:https://alop.uni-trier.de/event/alop-colloquium-with-sungho-shin-university-of-wisconsin-madison/
CATEGORIES:Colloquium
ORGANIZER;CN="RTG ALOP at Trier University":MAILTO:ALOP@uni-trier.de
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Berlin:20211108T160000
DTEND;TZID=Europe/Berlin:20211108T170000
DTSTAMP:20210811T093446Z
CREATED:20210519T085020Z
LAST-MODIFIED:20210811T093446Z
UID:5606-1636387200-1636390800@alop.uni-trier.de
SUMMARY:ALOP-Colloquium with Daniel Aloise\, Polytechnique Montréal
DESCRIPTION:On Monday\, November 8\, 2021 at 16:00 c.t.  Dr. Daniel Aloise\, Polytechnique Montréal will present his recent work at our colloquium.  \nTitle: Convex fuzzy k-medoids clustering \nAbstract: \nK-medoids clustering is among the most popular methods for cluster analysis\, but it carries several assumptions about the nature of the latent clusters. In this work\, we introduce the Convex Fuzzy k -Medoids (CFKM) model\, whose underlying formulation not only relaxes the assumption that objects must be assigned entirely to one and only one medoid\, but also that medoids must be assigned entirely to one and only one cluster. Moreover\, due to its convexity\, CFKM resolution is completely robust to initialization. We compare our model with two fuzzy k-medoids clustering models found in the literature: the Fuzzy k -Medoids (FKM) and the Fuzzy Clustering with Multi-Medoids (FMMdd)\, both solved approximately by heuristics because of their hard computational complexity. Our experiments in synthesized and real-world data sets reveal that our model can uniquely discover important aspects of clustered data which are inherently fuzzy in nature\, besides being more robust regarding the hyperparameters of the fuzzy clustering task. \nThis presentation will take place via ZOOM. A link will be e-mailed prior to the event.
URL:https://alop.uni-trier.de/event/alop-colloquium-with-daniel-alois-polytechnique-montreal/
CATEGORIES:Colloquium
ORGANIZER;CN="RTG ALOP at Trier University":MAILTO:ALOP@uni-trier.de
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Berlin:20210705T160000
DTEND;TZID=Europe/Berlin:20210705T170000
DTSTAMP:20210531T070017Z
CREATED:20210412T122101Z
LAST-MODIFIED:20210531T070017Z
UID:5498-1625500800-1625504400@alop.uni-trier.de
SUMMARY:ALOP-Colloquium with Frauke Liers\, FAU Erlangen-Nürnberg
DESCRIPTION:On Monday\, July 5\, 2021 at 16:00 c.t.  Prof. Dr. Frauke Liers with FAU Erlangen-Nuernberg will present her recent work at our colloquium. She will speak on the topic of  \n  \nData-Driven Robust Protection for Uncertain Optimization Problems \n  \nOne way of protecting against uncertainties that occur in real-world applications is to apply and to develop methodologies from robust optimization that determine best possible robust solutions that are feasible regardless of how uncertainties manifest themselves within predefined uncertainty sets. However\, it is often non-trivial to construct “suitable” uncertainty sets. In this talk\, we present two methodologies in this area. \nAt first\, we introduce a new iterative approach which uses scenario observations to learn more about the uncertainty over time\, enabling us to improve our solutions. The goal is to incorporate new information when it arrives and to improve our solution without resolving the entire robust counterpart. We illustrate the effectiveness of our procedure by numerical experiments on mixed-integer optimization instances from popular benchmark libraries as well as on a practical network design problem. The proposed algorithm is able to solve the problem significantly faster than solving equivalent reformulations. \nSubsequently\, we show that robust protection can also be used for a robust safe approximation of joint chance constrained in DC Optimal Power Flow problems. We propose an approach that replaces probabilistic constraints by robust constraints where the task consists in constructing uncertainty sets from historical data using the scenario approach by Margellos et al. (IEEE Transactions on Automatic Control\, 59 (2014)). The experimental tests demonstrate the effectiveness of this method and run times are very fast and lead to high-quality solutions. \n  \nThe first part is joint with Kevin Aigner\, Andreas Bärmann\, Kristin Braun\,  Oskar Schneider\, Sebastian Tschuppik (FAU Erlangen-Nürnberg)\, and Kartikey Sharma and Sebastian Pokutta (ZIB\, Berlin). The second part is joint with Kevin Aigner\, Jan-Patrick Clarner\, and Alexander Martin (FAU Erlangen-Nürnberg\, Germany). \nThis presentation will take place via ZOOM. A link will be e-mailed prior to the event. \n 
URL:https://alop.uni-trier.de/event/alop-colloquium-with-prof-dr-frauke-liers-fau-erlangen-nurnberg/
CATEGORIES:Colloquium
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Berlin:20210614T160000
DTEND;TZID=Europe/Berlin:20210614T170000
DTSTAMP:20210503T083753Z
CREATED:20210427T055753Z
LAST-MODIFIED:20210503T083753Z
UID:5536-1623686400-1623690000@alop.uni-trier.de
SUMMARY:ALOP-Colloquium with Laura Albert\, University of Wisconsin-Madison
DESCRIPTION:On Monday\, June 14\, 2021 at 16:00 c.t.  Prof. Dr. Laura Albert\, University of Wisconsin-Madison will present her recent work at our colloquium.  She will speak on a very popular contemporary topic \nSupporting academic researchers during the COVID-19 pandemic and beyond \nAbstract \nThe literature documents the many challenges faced by faculty from marginalized groups in terms of their hiring\, retention\, and advancement. The COVID-19 global pandemic has exasperated these inequities and has created serious challenges for many academic researchers\, especially faculty members with care responsibilities and female academics. Recent surveys of academic researchers indicate that women\, particularly those with young children\, have experienced a substantial decline in time devoted to research in the past year. It is crucial for academic communities and institutions to address these inequalities to reduce faculty burnout and retain faculty members from underrepresented groups. \nIn this talk\, Professor Laura Albert overview the challenges academics have faced during the pandemic. She will discuss some of the structural barriers for women academics and for academics with care responsibilities. She will give some examples from her own life and offer some guidance on best practices and institutional policies for those interested in creating spaces in operations research where everyone is welcomed and valued. \n  \nThis presentation will take place via ZOOM. A link will be e-mailed prior to the event. \nBio \nLaura Albert\, Ph.D.\, is a Professor of Industrial & Systems Engineering and a Harvey D. Spangler Faculty Scholar at the University of Wisconsin-Madison. Her research interests are in the field of operations research\, with a particular focus on discrete optimization with application to homeland security and emergency response problems. Dr. Albert’s research has been supported by the National Science Foundation\, the Department of Homeland Security\, the Department of the Army\, and Sandia National Laboratory. She has authored or co-authored more than 70 publications in archival journals and refereed proceedings. She has been awarded many honors for her research\, including the American Association for the Advancement of Science (AAAS) Fellow Award\, Institute of Industrial and Systems Engineers (IISE) Fellow Award\, the INFORMS Impact Prize\, four publication awards\, a National Science Foundation CAREER award\, a Fulbright Award\, and a Department of the Army Young Investigator Award. She is a Department Editor for IISE Transactions and is on or has been on six other journal Editorial Boards. Dr. Albert has served on the INFORMS Board as the Vice President for Marketing\, Communication\, and Outreach and served as the Assistant Dean for Graduate Affairs in the College of Engineering at UW-Madison. She is the author of the blogs “Punk Rock Operations Research” and “Badger Bracketology.” You can find her on twitter at @lauraalbertphd.
URL:https://alop.uni-trier.de/event/alop-colloquium-with-laura-albert-university-of-wisconsin-madison/
CATEGORIES:Colloquium
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Berlin:20210517T160000
DTEND;TZID=Europe/Berlin:20210517T170000
DTSTAMP:20210427T082855Z
CREATED:20210426T081448Z
LAST-MODIFIED:20210427T082855Z
UID:5531-1621267200-1621270800@alop.uni-trier.de
SUMMARY:ALOP-Kolloquium with Oliver Stein\, Karlsruher Institut für Technologie (KIT)
DESCRIPTION:On Monday\, May 17\, 2021 at 16:00 c.t. Prof. Dr. Oliver Stein\, Karlsruher Institut für Technologie (KIT) will present his recent work at our colloquium titled:  \nThe granularity concept in mixed-integer optimization \nGranularity is a geometrically motivated concept which relaxes the difficulties imposed by integrality \nconditions and often provides ways for determining good feasible points of mixed-integer optimization problems \nat low computational cost. \nWe explain how this concept leads to algorithms for the computation of feasible points in mixed-integer \nlinear\, convex\, and nonconvex optimization. We also comment on the treatment of equality constraints and \non the integration of the granularity idea into branch-and-bound frameworks. \nThis presentation will take place via ZOOM. A link will be e-mailed prior to the event.
URL:https://alop.uni-trier.de/event/alop-kolloquium-with-oliver-stein-karlsruher-institut-fur-technologie-kit/
CATEGORIES:Colloquium
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Berlin:20210510T160000
DTEND;TZID=Europe/Berlin:20210510T170000
DTSTAMP:20210505T075734Z
CREATED:20210308T100440Z
LAST-MODIFIED:20210505T075734Z
UID:5358-1620662400-1620666000@alop.uni-trier.de
SUMMARY:ALOP-Colloquium with Pascal Van Hentenryck\, Georgia Tech
DESCRIPTION:On Monday\, May 10\, 2021\, Prof. Dr. Pascal Van Hentenryck\, Georgia Tech will present his recent research titled: \nDifferential privacy of hierarchical Census data: An optimization approach  \nThis talk considers applications of a Census Bureau interested in releasing aggregate socio-economic data about a large population without revealing sensitive information about any individual. The released information can be the number of individuals living alone\, the number of cars they own\, or their salary brackets. Recent events have identified some of the privacy challenges faced by these organizations. To address them\, we present a novel differential-privacy mechanism for releasing hierarchical counts of individuals. The counts are reported at multiple granularities (e.g.\, the national\, state\, and county levels) and must be consistent across all levels. The core of the mechanism is an optimization model that redistributes the noise introduced to achieve differential privacy in order to meet the consistency constraints between the hierarchical levels. The key technical contribution of the paper shows that this optimization problem can be solved in polynomial time by exploiting the structure of its cost functions. Experimental results on very large\, real datasets show that the proposed mechanism provides improvements of up to two orders of magnitude in terms of computational efficiency and accuracy with respect to other state-of-the-art techniques. The talk also discusses various fairness issues arising in using differential privacy in downstream applications and how they can be mitigated. \nJoint work with Ferdinando Fioretto and Keyu Zhu \n  \nThis presentation will take place via Zoom. A link to participate in this presentation will be mailed shortly before the event. \nIf you wish to participate and receive and inviation\, please send an email to shawATuni-trier.de.
URL:https://alop.uni-trier.de/event/alop-colloquium-with-prof-dr-pascal-van-hentenryck-georgia-tech/
CATEGORIES:Colloquium
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Berlin:20210503T160000
DTEND;TZID=Europe/Berlin:20210503T170000
DTSTAMP:20210415T120317Z
CREATED:20210415T120317Z
LAST-MODIFIED:20210415T120317Z
UID:5504-1620057600-1620061200@alop.uni-trier.de
SUMMARY:ALOP-Colloquium with Prof. Dr. Bijan Mohammadi\, Montpellier University
DESCRIPTION:On Monday\, May 3\, 2021 at 16:00 c.t. Prof. Dr. Bijan Mohammadi\, Montpellier University\, will present his recent work at our colloquium.  He will speak about \nVariational nearshore dynamics  \nAbstract: \nMinimization principles are used in fluid-structure coupling to model sandy sea beds  evolution.The sandy bed is seen as a structure with low stiffness. We start with a model problem featuring the behavior of the coupling.Then water motion in shallow domains is described by the Saint Venant equations.This coupling bringing the bottom sea changes is based on the assumption that the bed adapts  to the flow in order to minimize some energy quantity togetherwith  minimal  sand transport.  The choice of the functional permits to include different physical quantities one think to play a role in the bottom morphodynamics.Hence\, the approach is also a tool for validating different modelling hypothesis.We also present tentative  direct and reverse uncertainty propagation procedures under the constraint of keeping the computational costcomparable to deterministic simulations.The different ingredients will be illustrated through coastal engineering applications.   \n  \nThe presentation will take place via Zoom. A link will be email prior to the event.\n \nIf you wish to receive a link and invitation to this presentation\, please send an email to shawATuni-trier.de
URL:https://alop.uni-trier.de/event/alop-colloquium-with-prof-dr-bijan-mohammadi-montpellier-university/
CATEGORIES:Colloquium
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Berlin:20210426T160000
DTEND;TZID=Europe/Berlin:20210426T170000
DTSTAMP:20210412T160553Z
CREATED:20210412T160553Z
LAST-MODIFIED:20210412T160553Z
UID:5500-1619452800-1619456400@alop.uni-trier.de
SUMMARY:ALOP-Colloquium with Dr. Ritesh Kumar Dubey of SRM University Chennai
DESCRIPTION:On Monday\, April 26\, 2021 at 16:00 c.t.  Dr. Ritesh Kumar Dubey of SRM University Chennai will present his recent work at our colloquium.  \n  \nTitle of the Talk: On numerical diffusion for entropy stable shock capturing schemes for hyperbolic conservation laws \nOne of the fundamental problems associated with the solution of hyperbolic conservation laws is the presence of inevitable discontinuities in it. This poses various challenges for the numerical approximation of such admissible solutions which eventually demand to construct numerical schemes which can yield physically correct non-oscillatory and crisp resolution of these discontinuities in the solution. To address this\, we use entropy stability framework and construct high order non-oscillatory entropy stable fluxes by devising suitable numerical diffusion using three different approaches (i) Non-linear stability (ii) Deep neural network and (iii) Optimization . This talk will give a comparative overview of these approaches along with theoretical and numerical results for benchmark test PDE cases. \n  \nThis presentation will take place via ZOOM. A link will be e-mailed prior to the event.
URL:https://alop.uni-trier.de/event/alop-colloquium-with-dr-ritesh-kumar-dubey-of-srm-university-chennai/
CATEGORIES:Colloquium
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Berlin:20210419T160000
DTEND;TZID=Europe/Berlin:20210419T170000
DTSTAMP:20210308T095421Z
CREATED:20210308T095421Z
LAST-MODIFIED:20210308T095421Z
UID:5356-1618848000-1618851600@alop.uni-trier.de
SUMMARY:ALOP-Colloquium with Prof. Dr. Tobias Harks\, Augsburg University
DESCRIPTION:On Monday\, April 19\, 2021 at 16:00 c.t. Prof. Dr. Tobias Harks of Augsburg University will present his recent work at our colloquium entitled \n  \nPricing in Resource Allocation Games \nWe consider a basic resource allocation game\, where the players’ strategy spaces are subsets of R^m and cost/utility functions are parameterized by some common vector u \in∈ R^m and\, otherwise\, only depend on the own strategy choice. A strategy of a player can be interpreted as a vector of resource consumption and a joint strategy profile naturally leads to an aggregate consumption vector. Resources can be priced\, that is\, the game is augmented by a price vector \lambda\inλR^m_+ and players have quasi-linear overall costs/utilities meaning that in addition to the original costs/utilities\, a player needs to pay the corresponding price per consumed unit. \n  \nWe investigate the following question: for which aggregated consumption vectors u can we find prices \lambdaλ that induce an equilibrium realizing the targeted consumption profile? For answering this question\, we revisit a well-known duality-based framework and derive several characterizations of the existence of such u and \lambda. We show that the characterization can help to unify parts of several largely independent streams in the literature – tolls in transportation systems\, Walrasian market equilibria\, trading networks\, energy networks and congestion control in communication networks. Besides reproving existing results we establish novel existence results by using methods from polyhedral combinatorics\, global optimization and discrete convexity. \nThe presentation will take place via Zoom. A link will be email prior to the event.\n \nIf you wish to receive a link and invitation to this presentation\, please send an email to shawATuni-trier.de
URL:https://alop.uni-trier.de/event/alop-colloquium-with-prof-dr-tobias-harks-augsburg-university/
CATEGORIES:Colloquium
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Berlin:20210125T160000
DTEND;TZID=Europe/Berlin:20210125T180000
DTSTAMP:20201013T043841Z
CREATED:20201013T042122Z
LAST-MODIFIED:20201013T043841Z
UID:5180-1611590400-1611597600@alop.uni-trier.de
SUMMARY:ALOP-Colloquium with Prof. Dr. Steven Gabriel\, University of Maryland
DESCRIPTION:On Monday\, January 25\, 2021 at 16:00 c.t. Prof. Dr. Steven Gabriel of the University of Maryland \, Baltimore will present his recent work at our colloquium entitled \n  \nA parametric programming approach to bilevel optimisation with lower-level variables in the upper level \nThis paper examines linearly constrained bilevel programming problems in which the upper-level\nobjective function depends on both the lower-level primal and dual optimal solutions. We parametrize\nthe lower-level solutions and thereby the upper-level objective function by the upper-level variables\nand argue that it may be non-convex and even discontinuous. However\, when the upper-level\nobjective is affine in the lower-level primal optimal solution\, the parametric function is piece-wise linear.\nWe show how this property facilitates the application of parametric programming and demonstrate how\nthe approach allows for decomposition of a separable lower-level problem. When the upper-level\nobjective is bilinear in the lower-level primal and dual optimal solutions\, we also provide an exact\nlinearisation method that reduces the bilevel problem to a single-level mixed-integer linear programme\n(MILP). We assess the performance of the parametric programming approach on two case studies of\nstrategic investment in electricity markets and benchmark against state-of-the-art MILP and non-linear\nsolution methods for bilevel optimisation problems. Preliminary results indicate substantial\ncomputational advantages over several standard solvers\, especially when the lower-level problem\nseparates into a large number of subproblems. Furthermore\, we show that the parametric\nprogramming approach succeeds in solving problems to global optimality for which standard methods\ncan fail. \nFor further information\, please refer to this article: Henrik C. Bylling\, Steven A. Gabriel & Trine K. Boomsma (2020) A parametric programming approach to bilevel optimisation with lower-level variables in the upper level\, Journal of the Operational Research Society\, 71:5\, 846-865\, DOI: 10.1080/01605682.2019.1590132\nTo link to this article: https://doi.org/10.1080/01605682.2019.1590132 \n  \nThis presentation will take place via ZOOM. A link will be e-mailed prior to the event.
URL:https://alop.uni-trier.de/event/alop-colloquium-with-steven-gabriel-university-of-maryland/
CATEGORIES:Colloquium
ORGANIZER;CN="RTG ALOP at Trier University":MAILTO:ALOP@uni-trier.de
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DTSTART;TZID=Europe/Berlin:20201214T160000
DTEND;TZID=Europe/Berlin:20201214T180000
DTSTAMP:20201207T162808Z
CREATED:20201008T115646Z
LAST-MODIFIED:20201207T162808Z
UID:5163-1607961600-1607968800@alop.uni-trier.de
SUMMARY:ALOP-Colloquium with Prof. Dr. Falk Hante\, HU Berlin
DESCRIPTION:On Monday\, December 14\, 2020 at 16:00\, Prof. Dr. Falk Hante\, Humbold Universität zu Berlin will present his recent work at our colloquium. \n  \nTitle: Sequential action control for stabilization of PDE-dynamical systems \nWe present sequential action control as a framework suitable for control and stabilization of PDE-dynamical problems. As a variant of a moving horizon method\, but in contrast to classical model predictive control approaches\, the control synthesis does not require to compute solutions of dynamic optimization problems. Moreover\, the control principle can be easily extended to piecewise linear switched systems and other heterogenuous optimal control problems being motivated\, for example\, by gas network operation. We use Riccati theory for the qualitative analysis of the method and present results prototypically for the stabilization of an unstable reaction-diffusion process. \nReferences:\n[1] Y. Brodskyi\, F.M. Hante\, A. Seidel: Stabilization of Partial Differential Equations by Sequential Action Control. TRR154 Preprint 271\, 2019. \n  \nThis presentation will take place via ZOOM. A link will be e-mailed prior to the event.
URL:https://alop.uni-trier.de/event/alop-colloquium-with-prof-dr-falk-hante-hu-berlin/
CATEGORIES:Colloquium
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