41 research outputs found
The Impact of Symmetry Handling for the Stable Set Problem via Schreier-Sims Cuts
Symmetry handling inequalities (SHIs) are an appealing and popular tool for
handling symmetries in integer programming. Despite their practical
application, little is known about their interaction with optimization
problems. This article focuses on Schreier-Sims (SST) cuts, a recently
introduced family of SHIs, and investigate their impact on the computational
and polyhedral complexity of optimization problems. Given that SST cuts are not
unique, a crucial question is to understand how different constructions of SST
cuts influence the solving process.
First, we observe that SST cuts do not increase the computational complexity
of solving a linear optimization problem over any polytope . However,
separating the integer hull of enriched by SST cuts can be NP-hard, even if
is integral and has a compact formulation. We study this phenomenon more
in-depth for the stable set problem, particularly for subclasses of perfect
graphs. For bipartite graphs, we give a complete characterization of the
integer hull after adding SST cuts based on odd-cycle inequalities. For
trivially perfect graphs, we observe that the separation problem is still
NP-hard after adding a generic set of SST cuts. Our main contribution is to
identify a specific class of SST cuts, called stringent SST cuts, that keeps
the separation problem polynomial and a complete set of inequalities, namely
SST clique cuts, that yield a complete linear description.
We complement these results by giving SST cuts based presolving techniques
and provide a computational study to compare the different approaches. In
particular, our newly identified stringent SST cuts dominate other approaches
A Unified Framework for Symmetry Handling
Handling symmetries in optimization problems is essential for devising
efficient solution methods. In this article, we present a general framework
that captures many of the already existing symmetry handling methods (SHMs).
While these SHMs are mostly discussed independently from each other, our
framework allows to apply different SHMs simultaneously and thus outperforming
their individual effect. Moreover, most existing SHMs only apply to binary
variables. Our framework allows to easily generalize these methods to general
variable types. Numerical experiments confirm that our novel framework is
superior to the state-of-the-art SHMs implemented in the solver SCIP
Impact of Symmetries in Graph Clustering
Diese Dissertation beschĂ€ftigt sich mit der durch die Automorphismusgruppe definierten Symmetrie von Graphen und wie sich diese auf eine Knotenpartition, als Ergebnis von Graphenclustering, auswirkt. Durch eine Analyse von nahezu 1700 Graphen aus verschiedenen Anwendungsbereichen kann gezeigt werden, dass mehr als 70 % dieser Graphen Symmetrien enthalten. Dies bildet einen Gegensatz zum kombinatorischen Beweis, der besagt, dass die Wahrscheinlichkeit eines zufĂ€lligen Graphen symmetrisch zu sein bei zunehmender GröĂe gegen Null geht. Das Ergebnis rechtfertigt damit die Wichtigkeit weiterer Untersuchungen, die auf mögliche Auswirkungen der Symmetrie eingehen. Bei der Analyse werden sowohl sehr kleine Graphen (10 000 000 Knoten/>25 000 000 Kanten) berĂŒcksichtigt.
Weiterhin wird ein theoretisches Rahmenwerk geschaffen, das zum einen die detaillierte Quantifizierung von Graphensymmetrie erlaubt und zum anderen StabilitĂ€t von Knotenpartitionen hinsichtlich dieser Symmetrie formalisiert. Eine Partition der Knotenmenge, die durch die Aufteilung in disjunkte Teilmengen definiert ist, wird dann als stabil angesehen, wenn keine Knoten symmetriebedingt von der einen in die andere Teilmenge abgebildet werden und dadurch die Partition verĂ€ndert wird. Zudem wird definiert, wie eine mögliche Zerlegbarkeit der Automorphismusgruppe in unabhĂ€ngige Untergruppen als lokale Symmetrie interpretiert werden kann, die dann nur Auswirkungen auf einen bestimmten Bereich des Graphen hat. Um die Auswirkungen der Symmetrie auf den gesamten Graphen und auf Partitionen zu quantifizieren, wird auĂerdem eine Entropiedefinition prĂ€sentiert, die sich an der Analyse dynamischer Systeme orientiert. Alle Definitionen sind allgemein und können daher fĂŒr beliebige Graphen angewandt werden. Teilweise ist sogar eine Anwendbarkeit fĂŒr beliebige Clusteranalysen gegeben, solange deren Ergebnis in einer Partition resultiert und sich eine Symmetrierelation auf den Datenpunkten als Permutationsgruppe angeben lĂ€sst.
Um nun die tatsĂ€chliche Auswirkung von Symmetrie auf Graphenclustering zu untersuchen wird eine zweite Analyse durchgefĂŒhrt. Diese kommt zum Ergebnis, dass von 629 untersuchten symmetrischen Graphen 72 eine instabile Partition haben. FĂŒr die Analyse werden die Definitionen des theoretischen Rahmenwerks verwendet. Es wird auĂerdem festgestellt, dass die LokalitĂ€t der Symmetrie eines Graphen maĂgeblich beeinflusst, ob dessen Partition stabil ist oder nicht. Eine hohe LokalitĂ€t resultiert meist in einer stabilen Partition und eine stabile Partition impliziert meist eine hohe LokalitĂ€t.
Bevor die obigen Ergebnisse beschrieben und definiert werden, wird eine umfassende EinfĂŒhrung in die verschiedenen benötigten Grundlagen gegeben. Diese umfasst die formalen Definitionen von Graphen und statistischen Graphmodellen, Partitionen, endlichen Permutationsgruppen, Graphenclustering und Algorithmen dafĂŒr, sowie von Entropie. Ein separates Kapitel widmet sich ausfĂŒhrlich der Graphensymmetrie, die durch eine endliche Permutationsgruppe, der Automorphismusgruppe, beschrieben wird. AuĂerdem werden Algorithmen vorgestellt, die die Symmetrie von Graphen ermitteln können und, teilweise, auch das damit eng verwandte Graphisomorphie Problem lösen.
Am Beispiel von Graphenclustering gibt die Dissertation damit Einblicke in mögliche Auswirkungen von Symmetrie in der Datenanalyse, die so in der Literatur bisher wenig bis keine Beachtung fanden
Symmetry reduction in convex optimization with applications in combinatorics
This dissertation explores different approaches to and applications of symmetry reduction in convex optimization. Using tools from semidefinite programming, representation theory and algebraic combinatorics, hard combinatorial problems are solved or bounded. The first chapters consider the Jordan reduction method, extend the method to optimization over the doubly nonnegative cone, and apply it to quadratic assignment problems and energy minimization on a discrete torus. The following chapter uses symmetry reduction as a proving tool, to approach a problem from queuing theory with redundancy scheduling. The final chapters propose generalizations and reductions of flag algebras, a powerful tool for problems coming from extremal combinatorics
The Fifteenth Marcel Grossmann Meeting
The three volumes of the proceedings of MG15 give a broad view of all aspects of gravitational physics and astrophysics, from mathematical issues to recent observations and experiments. The scientific program of the meeting included 40 morning plenary talks over 6 days, 5 evening popular talks and nearly 100 parallel sessions on 71 topics spread over 4 afternoons. These proceedings are a representative sample of the very many oral and poster presentations made at the meeting.Part A contains plenary and review articles and the contributions from some parallel sessions, while Parts B and C consist of those from the remaining parallel sessions. The contents range from the mathematical foundations of classical and quantum gravitational theories including recent developments in string theory, to precision tests of general relativity including progress towards the detection of gravitational waves, and from supernova cosmology to relativistic astrophysics, including topics such as gamma ray bursts, black hole physics both in our galaxy and in active galactic nuclei in other galaxies, and neutron star, pulsar and white dwarf astrophysics. Parallel sessions touch on dark matter, neutrinos, X-ray sources, astrophysical black holes, neutron stars, white dwarfs, binary systems, radiative transfer, accretion disks, quasars, gamma ray bursts, supernovas, alternative gravitational theories, perturbations of collapsed objects, analog models, black hole thermodynamics, numerical relativity, gravitational lensing, large scale structure, observational cosmology, early universe models and cosmic microwave background anisotropies, inhomogeneous cosmology, inflation, global structure, singularities, chaos, Einstein-Maxwell systems, wormholes, exact solutions of Einstein's equations, gravitational waves, gravitational wave detectors and data analysis, precision gravitational measurements, quantum gravity and loop quantum gravity, quantum cosmology, strings and branes, self-gravitating systems, gamma ray astronomy, cosmic rays and the history of general relativity
The Fifteenth Marcel Grossmann Meeting
The three volumes of the proceedings of MG15 give a broad view of all aspects of gravitational physics and astrophysics, from mathematical issues to recent observations and experiments. The scientific program of the meeting included 40 morning plenary talks over 6 days, 5 evening popular talks and nearly 100 parallel sessions on 71 topics spread over 4 afternoons. These proceedings are a representative sample of the very many oral and poster presentations made at the meeting.Part A contains plenary and review articles and the contributions from some parallel sessions, while Parts B and C consist of those from the remaining parallel sessions. The contents range from the mathematical foundations of classical and quantum gravitational theories including recent developments in string theory, to precision tests of general relativity including progress towards the detection of gravitational waves, and from supernova cosmology to relativistic astrophysics, including topics such as gamma ray bursts, black hole physics both in our galaxy and in active galactic nuclei in other galaxies, and neutron star, pulsar and white dwarf astrophysics. Parallel sessions touch on dark matter, neutrinos, X-ray sources, astrophysical black holes, neutron stars, white dwarfs, binary systems, radiative transfer, accretion disks, quasars, gamma ray bursts, supernovas, alternative gravitational theories, perturbations of collapsed objects, analog models, black hole thermodynamics, numerical relativity, gravitational lensing, large scale structure, observational cosmology, early universe models and cosmic microwave background anisotropies, inhomogeneous cosmology, inflation, global structure, singularities, chaos, Einstein-Maxwell systems, wormholes, exact solutions of Einstein's equations, gravitational waves, gravitational wave detectors and data analysis, precision gravitational measurements, quantum gravity and loop quantum gravity, quantum cosmology, strings and branes, self-gravitating systems, gamma ray astronomy, cosmic rays and the history of general relativity
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Queer quests: journeying through manifestations of queerness in video games
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