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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
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DTSTART;TZID=Europe/Berlin:20240226T160000
DTEND;TZID=Europe/Berlin:20240226T170000
DTSTAMP:20240118T072334Z
CREATED:20231019T094016Z
LAST-MODIFIED:20240118T072334Z
UID:7307-1708963200-1708966800@alop.uni-trier.de
SUMMARY:ALOP Colloquium with Boris Detienne
DESCRIPTION:On Monday\, February 26\, 2024 at 16:00 c.t. Prof. Boris Detienne\, University of Bordeaux\, will speak at the ALOP Colloquium about his recent work. \n  \nThe Benders-by-batch algorithm to solve two-stage stochastic linear programs \nAbstract: \nIn this talk\, we will introduce a new exact algorithm to solve two-stage stochastic linear programs. Based on the multicut Benders reformulation of such problems\, with one subproblem for each scenario\, this method relies on a partition of the subproblems into batches. The key idea is to solve at most iterations only a small proportion of the subproblems by detecting as soon as possible that a first-stage candidate solution cannot be proven optimal. We also propose a general framework to stabilize our algorithm\, and show its finite convergence and exact behavior. We report an extensive computational study on large-scale instances of stochastic optimization literature that shows the efficiency of the proposed algorithm compared to nine alternative algorithms from the literature. We also obtain significant additional computational time savings using the primal stabilization schemes \n  \nPlease join us at 16:00 c.t. in HS 9. \n 
URL:https://alop.uni-trier.de/event/alop-colloquium-with-boris-detienne/
LOCATION:Trier University\, E Building\, Universitätsring 15\, Trier\, Germany
ORGANIZER;CN="RTG ALOP at Trier University":MAILTO:ALOP@uni-trier.de
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