From i.brunke@inf.fu-berlin.de Thu Oct 18 12:56:10 2018 Received: from outpost1.zedat.fu-berlin.de ([130.133.4.66]) by list1.zedat.fu-berlin.de (Exim 4.85) for facets-of-complexity@lists.fu-berlin.de with esmtps (TLSv1.2:DHE-RSA-AES256-GCM-SHA384:256) (envelope-from ) id <1gD5yM-004BnM-C7>; Thu, 18 Oct 2018 12:56:10 +0200 Received: from inpost2.zedat.fu-berlin.de ([130.133.4.69]) by outpost.zedat.fu-berlin.de (Exim 4.85) for facets-of-complexity@lists.fu-berlin.de with esmtps (TLSv1.2:DHE-RSA-AES256-GCM-SHA384:256) (envelope-from ) id <1gD5yM-001nYV-8R>; Thu, 18 Oct 2018 12:56:10 +0200 Received: from punkt.imp.fu-berlin.de ([160.45.40.245]) by inpost2.zedat.fu-berlin.de (Exim 4.85) for facets-of-complexity@lists.fu-berlin.de with esmtpsa (TLSv1.2:AES128-SHA:128) (envelope-from ) id <1gD5yL-002tvK-MQ>; Thu, 18 Oct 2018 12:56:10 +0200 From: Ita Brunke To: facets-of-complexity@lists.fu-berlin.de Message-ID: Date: Thu, 18 Oct 2018 12:56:09 +0200 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="------------552737630548D06E74A94E33" Content-Language: en-US X-Originating-IP: 160.45.40.245 X-ZEDAT-Hint: A X-purgate: clean X-purgate-type: clean X-purgate-ID: 151147::1539860170-000004D7-54EB5312/0/0 X-Bogosity: Ham, tests=bogofilter, spamicity=0.013416, version=1.2.4 X-Spam-Flag: NO X-Spam-Status: No, score=-50.0 required=5.0 tests=ALL_TRUSTED,HTML_MESSAGE X-Spam-Checker-Version: SpamAssassin 3.4.1 on Tokelau.ZEDAT.FU-Berlin.DE X-Spam-Level: Subject: [Facets-of-complexity] Invitation to Monday Lecture & Colloquium - October 22nd 2018 X-BeenThere: facets-of-complexity@lists.fu-berlin.de X-Mailman-Version: 2.1.29 Precedence: list List-Id: announcements of Monday lectures and other events List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 18 Oct 2018 10:56:10 -0000 This is a multi-part message in MIME format. --------------552737630548D06E74A94E33 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit You are cordially invited to our Monday Lecture & Colloquium on October 22nd at 14:15 h & 16:00 h at TU Berlin. *_Location_**: ** * *R**oom MA 041 - Ground Floor* Technische Universität Berlin Straße des 17. Juni 136 10623 Berlin *_Time_: **Monday, October 22nd - 14:15 h* *_Lecture_: Alexander Fink (Queen Mary University London)* *_Title_: Stiefel tropical linear spaces * *_Abstract_:* As we tell our undergraduates, if K is a field, then there are a great number of different ways to describe a linear subspace of K^n. If the base is an algebraic object with less structure than a field, linear algebra becomes more subtle, and some of these descriptions cease to agree. One such setting is tropical geometry. Tropical geometers have reached consensus as to what the "correct" notion of tropical linear subspace is (one way to get it is by a vector of determinants). My subject will be one of the "wrong" descriptions, namely row spaces of matrices, which only produces a subset of the tropical linear spaces. Applications include generalisations of Mason's results from the '70s on presentations of transversal matroids, and a construction in the new area of tropical ideal theory. This work is variously joint with Felipe Rinc\'on, Jorge Alberto Olarte, and Jeffrey and Noah Giansiracusa. _*Coffee & Tea Break*_*:*_* *_* R**oom MA 316 - Third Floor* *_Time_: **Monday, ***October 22nd* - 16:00 h* *_Colloquium_: Akiyoshi Tsuchiya (Osaka University) * *_Title_: Polyhedral characterizations of perfect graphs * *_Abstract_:* Perfect graphs are important objects in graph theory. The perfect graphs include many important families of graphs, and serve to unify results relating colorings and cliques in those families. One of the most famous and most important results is the strong perfect graph theorem conjectured by Claude Berge and proved by Chudnovsky, Robertson and Thomas. This theorem characterizes perfect graphs. Our interest is to give other characterizations of perfect graphs. In this talk, we construct several lattice polytopes arising from a finite simple graph and characterize when the graph is perfect in terms of the lattice polytopes. This talk is based on joint work with Takayuki Hibi and Hidefumi Ohsugi. --------------552737630548D06E74A94E33 Content-Type: text/html; charset=utf-8 Content-Transfer-Encoding: 8bit

You are cordially invited to our Monday Lecture & Colloquium on October 22nd at 14:15 h & 16:00 h at TU Berlin.

Location:

Room MA 041 - Ground Floor
Technische Universität Berlin
Straße des 17. Juni 136
10623 Berlin

Time: Monday, October 22nd - 14:15 h

Lecture: Alexander Fink (Queen Mary University London)

Title: Stiefel tropical linear spaces

Abstract:

As we tell our undergraduates, if K is a field, then there are a great number of different ways to describe a linear subspace of K^n. If the base is an algebraic object with less structure than a field, linear algebra becomes more subtle, and some of these descriptions cease to agree. One such setting is tropical geometry. Tropical geometers have reached consensus as to what the "correct" notion of tropical linear subspace is (one way to get it is by a vector of determinants). My subject will be one of the "wrong" descriptions, namely row spaces of matrices, which only produces a subset of the tropical linear spaces. Applications include generalisations of Mason's results from the '70s on presentations of transversal matroids, and a construction in the new area of tropical ideal theory.

This work is variously joint with Felipe Rinc\'on, Jorge Alberto Olarte, and Jeffrey and Noah Giansiracusa.


Coffee & Tea Break :

Room MA 316 - Third Floor

Time: Monday, October 22nd - 16:00 h

Colloquium: Akiyoshi Tsuchiya (Osaka University)

Title: Polyhedral characterizations of perfect graphs

Abstract:

Perfect graphs are important objects in graph theory. The perfect graphs include many important families of graphs, and serve to unify results relating colorings and cliques in those families. One of the most famous and most important results is the strong perfect graph theorem conjectured by Claude Berge and proved by Chudnovsky, Robertson and Thomas. This theorem characterizes perfect graphs. Our interest is to give other characterizations of perfect graphs. In this talk, we construct several lattice polytopes arising from a finite simple graph and characterize when the graph is perfect in terms of the lattice polytopes.

This talk is based on joint work with Takayuki Hibi and Hidefumi Ohsugi.

--------------552737630548D06E74A94E33-- From i.brunke@inf.fu-berlin.de Thu Oct 25 12:59:40 2018 Received: from outpost1.zedat.fu-berlin.de ([130.133.4.66]) by list1.zedat.fu-berlin.de (Exim 4.85) for facets-of-complexity@lists.fu-berlin.de with esmtps (TLSv1.2:DHE-RSA-AES256-GCM-SHA384:256) (envelope-from ) id <1gFdMa-002AcH-1Q>; Thu, 25 Oct 2018 12:59:40 +0200 Received: from inpost2.zedat.fu-berlin.de ([130.133.4.69]) by outpost.zedat.fu-berlin.de (Exim 4.85) for facets-of-complexity@lists.fu-berlin.de with esmtps (TLSv1.2:DHE-RSA-AES256-GCM-SHA384:256) (envelope-from ) id <1gFdMZ-0042O6-UR>; Thu, 25 Oct 2018 12:59:39 +0200 Received: from punkt.imp.fu-berlin.de ([160.45.40.245]) by inpost2.zedat.fu-berlin.de (Exim 4.85) for facets-of-complexity@lists.fu-berlin.de with esmtpsa (TLSv1.2:AES128-SHA:128) (envelope-from ) id <1gFdMZ-001Ehe-OV>; Thu, 25 Oct 2018 12:59:39 +0200 From: Ita Brunke To: facets-of-complexity@lists.fu-berlin.de Message-ID: <05215f79-79f1-6f49-ac44-e957ea1ec52a@inf.fu-berlin.de> Date: Thu, 25 Oct 2018 12:59:39 +0200 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="------------B0C79390DF0CF419FB05C14C" Content-Language: en-US X-Originating-IP: 160.45.40.245 X-ZEDAT-Hint: A X-purgate: clean X-purgate-type: clean X-purgate-ID: 151147::1540465180-000004D7-0BA83D89/0/0 X-Bogosity: Ham, tests=bogofilter, spamicity=0.426363, version=1.2.4 X-Spam-Flag: NO X-Spam-Status: No, score=-50.0 required=5.0 tests=ALL_TRUSTED,HTML_MESSAGE X-Spam-Checker-Version: SpamAssassin 3.4.1 on Tokelau.ZEDAT.FU-Berlin.DE X-Spam-Level: Subject: [Facets-of-complexity] Invitation to Monday Colloquium - October 29th 2018 X-BeenThere: facets-of-complexity@lists.fu-berlin.de X-Mailman-Version: 2.1.29 Precedence: list List-Id: announcements of Monday lectures and other events List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 25 Oct 2018 10:59:40 -0000 This is a multi-part message in MIME format. --------------B0C79390DF0CF419FB05C14C Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit You are cordially invited to our next Monday Colloquium on October 29th at 16:00 h at TU Berlin. *_Location_**: ** * *Room MA 041 - Ground Floor* Technische Universität Berlin Straße des 17. Juni 136 10623 Berlin *_Time_: **Monday, October 29th - 16:00 h* *_Colloquium_: Jan Goedgebeur (Ghent University**)* *_Title_: **Obstructions for 3-coloring graphs with one forbidden induced subgraph* *_Abstract_:* For several graph classes without long induced paths there exists a finite forbidden subgraph characterization for k-colourability. Such a finite set of minimal obstructions allows to provide a “no-certificate" which proves that a graph is not k-colourable. We prove that there are only finitely many 4-critical P6-free graphs, and give the complete list that consists of 24 graphs. In particular, we obtain a certifying algorithm for 3-colouring P6-free graphs, which solves an open problem posed by Golovach et al. (Here, P6 denotes the induced path on six vertices.) Our result leads to the following dichotomy theorem: if H is a connected graph, then there are finitely many 4-critical H-free graphs if and only if H is a subgraph of P6. This answers a question of Seymour. The proof of our main result involves two distinct automatic proofs, and an extensive structural analysis by hand. In this talk we will mainly focus on the algorithmic results by presenting a new algorithm for generating all minimal forbidden subgraphs to k-colourability for given graph classes. This algorithm (combined with new theoretical results) has been successfully applied to fully characterise all forbidden subgraphs for k-colourability for various classes of graphs without long induced paths. This is joint work with Maria Chudnovsky, Oliver Schaudt and Mingxian Zhong. /Exceptionally, there will be no lecture and only this colloquium, because of the 'Einstein Workshop'./ --------------B0C79390DF0CF419FB05C14C Content-Type: text/html; charset=utf-8 Content-Transfer-Encoding: 8bit

You are cordially invited to our next Monday Colloquium on October 29th at 16:00 h at TU Berlin.

Location:

Room MA 041 - Ground Floor
Technische Universität Berlin
Straße des 17. Juni 136
10623 Berlin

Time: Monday, October 29th - 16:00 h

Colloquium: Jan Goedgebeur (Ghent University)

Title: Obstructions for 3-coloring graphs with one forbidden induced subgraph

Abstract:

For several graph classes without long induced paths there exists a finite forbidden subgraph characterization for k-colourability. Such a finite set of minimal obstructions allows to provide a “no-certificate" which proves that a graph is not k-colourable. We prove that there are only finitely many 4-critical P6-free graphs, and give the complete list that consists of 24 graphs. In particular, we obtain a certifying algorithm for 3-colouring P6-free graphs, which solves an open problem posed by Golovach et al. (Here, P6 denotes the induced path on six vertices.) Our result leads to the following dichotomy theorem: if H is a connected graph, then there are finitely many 4-critical H-free graphs if and only if H is a subgraph of P6. This answers a question of Seymour. The proof of our main result involves two distinct automatic proofs, and an extensive structural analysis by hand. In this talk we will mainly focus on the algorithmic results by presenting a new algorithm for generating all minimal forbidden subgraphs to k-colourability for given graph classes. This algorithm (combined with new theoretical results) has been successfully applied to fully characterise all forbidden subgraphs for k-colourability for various classes of graphs without long induced paths.

This is joint work with Maria Chudnovsky, Oliver Schaudt and Mingxian Zhong.

Exceptionally, there will be no lecture and only this colloquium, because of the 'Einstein Workshop'.
--------------B0C79390DF0CF419FB05C14C-- From i.brunke@inf.fu-berlin.de Thu Nov 01 12:41:47 2018 Received: from outpost1.zedat.fu-berlin.de ([130.133.4.66]) by list1.zedat.fu-berlin.de (Exim 4.85) for facets-of-complexity@lists.fu-berlin.de with esmtps (TLSv1.2:DHE-RSA-AES256-GCM-SHA384:256) (envelope-from ) id <1gIBMA-003HfU-TZ>; Thu, 01 Nov 2018 12:41:47 +0100 Received: from inpost2.zedat.fu-berlin.de ([130.133.4.69]) by outpost.zedat.fu-berlin.de (Exim 4.85) for facets-of-complexity@lists.fu-berlin.de with esmtps (TLSv1.2:DHE-RSA-AES256-GCM-SHA384:256) (envelope-from ) id <1gIBMA-002hjB-QB>; Thu, 01 Nov 2018 12:41:46 +0100 Received: from punkt.imp.fu-berlin.de ([160.45.40.245]) by inpost2.zedat.fu-berlin.de (Exim 4.85) for facets-of-complexity@lists.fu-berlin.de with esmtpsa (TLSv1.2:AES128-SHA:128) (envelope-from ) id <1gIBMA-0030HW-Fu>; Thu, 01 Nov 2018 12:41:46 +0100 From: Ita Brunke To: facets-of-complexity@lists.fu-berlin.de Message-ID: <9b0d8627-1fe0-395c-8611-947a824400ff@inf.fu-berlin.de> Date: Thu, 1 Nov 2018 12:41:46 +0100 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="------------48B0CBBC3FF41BA60B153F33" Content-Language: en-US X-Originating-IP: 160.45.40.245 X-ZEDAT-Hint: A X-purgate: clean X-purgate-type: clean X-purgate-ID: 151147::1541072506-000004BE-2F4D1F79/0/0 X-Bogosity: Ham, tests=bogofilter, spamicity=0.095215, version=1.2.4 X-Spam-Flag: NO X-Spam-Status: No, score=-50.0 required=5.0 tests=ALL_TRUSTED,HTML_MESSAGE X-Spam-Checker-Version: SpamAssassin 3.4.2 on Palau.ZEDAT.FU-Berlin.DE X-Spam-Level: Subject: [Facets-of-complexity] Invitation to Monday Lecture & Colloquium - November 5th 2018 X-BeenThere: facets-of-complexity@lists.fu-berlin.de X-Mailman-Version: 2.1.29 Precedence: list List-Id: announcements of Monday lectures and other events List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 01 Nov 2018 11:41:47 -0000 This is a multi-part message in MIME format. --------------48B0CBBC3FF41BA60B153F33 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit You are cordially invited to our Monday Lecture & Colloquium on November 5th at 14:15 h & 16:00 h at HU Berlin. *_Location_**: ** * *Room 3.408 (House 3 / 4th Floor)* *[British Reading]* Humboldt-Universität zu Berlin Institut für Informatik Johann von Neumann-Haus Rudower Chaussee 25 12489 Berlin *_Time_: **Monday, November 5th - 14:15 h* *_Lecture_: Henning Meyerhenke (Humboldt-Universität zu Berlin)* *_Title_: Algorithms for Large-scale Network Analysis * *_Abstract_:* Network centrality measures indicate the importance of nodes (or edges) in a network. In this talk we will discuss a few popular measures and algorithms for computing complete or partial node rankings based on these measures. These algorithms are implemented in NetworKit, an open-source framework for large-scale network analysis, on which we provide an overview, too. One focus of the talk will be on techniques for speeding up a greedy (1-1/e)-approximation algorithm for the NP-hard group closeness centrality problem. Compared to a straightforward implementation, our approach is orders of magnitude faster and, compared to a heuristic proposed by Chen et al., we always find a solution with better quality in a comparable running time in our experiments. Our method Greedy++ allows us to approximate the group with maximum closeness centrality on networks with up to hundreds of millions of edges in minutes or at most a few hours. In a comparison with the optimum, our experiments show that the solution found by Greedy++ is actually much better than the theoretical guarantee. _*Coffee & Tea Break*_*:*_* *_* **Room 3.321 (House 3 / 3rd Floor)* *[British Reading]* *_Time_: **Monday, ***November 5th* - 16:00 h* *_Colloquium_: Alexander van der Grinten (Universität zu Köln) * *_Title_: Scalable Katz Ranking Computation * *_Abstract_:* Network analysis defines a number of centrality measures to identify the most central nodes in a network. Fast computation of those measures is a major challenge in algorithmic network analysis. Aside from closeness and betweenness, Katz centrality is one of the established centrality measures. We consider the problem of computing rankings for Katz centrality. In particular, we propose upper and lower bounds on the Katz score of a given node. While previous approaches relied on numerical approximation or heuristics to compute Katz centrality rankings, we construct an algorithm that iteratively improves those upper and lower bounds until a correct Katz ranking is obtained. For a certain class of inputs, this yields an optimal algorithm for Katz ranking computation. Furthermore, Experiments demonstrate that our algorithm outperforms both numerical approaches and heuristics with speedups between 1.5x and 3.5x, depending on the desired quality guarantees. Specifically, we provide efficient parallel CPU and GPU implementations of the algorithms that enable near real-time Katz centrality computation for graphs with hundreds of millions of nodes in fractions of seconds. --------------48B0CBBC3FF41BA60B153F33 Content-Type: text/html; charset=utf-8 Content-Transfer-Encoding: 8bit

You are cordially invited to our Monday Lecture & Colloquium on November 5th at 14:15 h & 16:00 h at HU Berlin.

Location:

Room 3.408 (House 3 / 4th Floor) [British Reading]
Humboldt-Universität zu Berlin
Institut für Informatik
Johann von Neumann-Haus
Rudower Chaussee 25
12489 Berlin

Time: Monday, November 5th - 14:15 h

Lecture: Henning Meyerhenke (Humboldt-Universität zu Berlin)

Title: Algorithms for Large-scale Network Analysis

Abstract:

Network centrality measures indicate the importance of nodes (or edges) in a network. In this talk we will discuss a few popular measures and algorithms for computing complete or partial node rankings based on these measures. These algorithms are implemented in NetworKit, an open-source framework for large-scale network analysis, on which we provide an overview, too.

One focus of the talk will be on techniques for speeding up a greedy (1-1/e)-approximation algorithm for the NP-hard group closeness centrality problem.
Compared to a straightforward implementation, our approach is orders of magnitude faster and, compared to a heuristic proposed by Chen et al., we always find a solution with better quality in a comparable running time in our experiments. Our
method Greedy++ allows us to approximate the group with maximum closeness centrality on networks with up to hundreds of millions of edges in minutes or at most a few hours.
In a comparison with the optimum, our experiments show that the solution found by Greedy++ is actually much better than the theoretical guarantee.


Coffee & Tea Break :

Room 3.321 (House 3 / 3rd Floor) [British Reading]

Time: Monday, November 5th - 16:00 h

Colloquium: Alexander van der Grinten (Universität zu Köln)

Title: Scalable Katz Ranking Computation

Abstract:

Network analysis defines a number of centrality measures to identify the most central nodes in a network. Fast computation of those measures is a major challenge in algorithmic network analysis. Aside from closeness and betweenness, Katz centrality is one of the established centrality measures. We consider the problem of computing rankings for Katz centrality. In particular, we propose upper and lower bounds on the Katz score of a given node. While previous approaches relied on numerical approximation or heuristics to compute Katz centrality rankings, we construct an algorithm that iteratively improves those upper and lower bounds until a correct Katz ranking is obtained. For a certain class of inputs, this yields an optimal algorithm for Katz ranking computation. Furthermore, Experiments demonstrate that our algorithm outperforms both numerical approaches and heuristics with speedups between 1.5x and 3.5x, depending on the desired quality guarantees. Specifically, we provide efficient parallel CPU and GPU implementations of the algorithms that enable near real-time Katz centrality computation for graphs with hundreds of millions of nodes in fractions of seconds.

--------------48B0CBBC3FF41BA60B153F33-- From i.brunke@inf.fu-berlin.de Thu Nov 08 12:19:07 2018 Received: from outpost1.zedat.fu-berlin.de ([130.133.4.66]) by list1.zedat.fu-berlin.de (Exim 4.85) for facets-of-complexity@lists.fu-berlin.de with esmtps (TLSv1.2:DHE-RSA-AES256-GCM-SHA384:256) (envelope-from ) id <1gKiL4-003eTb-A0>; Thu, 08 Nov 2018 12:19:06 +0100 Received: from inpost2.zedat.fu-berlin.de ([130.133.4.69]) by outpost.zedat.fu-berlin.de (Exim 4.85) for facets-of-complexity@lists.fu-berlin.de with esmtps (TLSv1.2:DHE-RSA-AES256-GCM-SHA384:256) (envelope-from ) id <1gKiL4-001r5u-6L>; Thu, 08 Nov 2018 12:19:06 +0100 Received: from punkt.imp.fu-berlin.de ([160.45.40.245]) by inpost2.zedat.fu-berlin.de (Exim 4.85) for facets-of-complexity@lists.fu-berlin.de with esmtpsa (TLSv1.2:AES128-SHA:128) (envelope-from ) id <1gKiL3-0021Ms-Op>; Thu, 08 Nov 2018 12:19:06 +0100 From: Ita Brunke To: facets-of-complexity@lists.fu-berlin.de Message-ID: <4dad45c3-2c8b-2d53-4888-2622904632c7@inf.fu-berlin.de> Date: Thu, 8 Nov 2018 12:19:05 +0100 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="------------6EB16D1C3B5AC5F9FE472636" Content-Language: en-US X-Originating-IP: 160.45.40.245 X-ZEDAT-Hint: A X-purgate: clean X-purgate-type: clean X-purgate-ID: 151147::1541675946-000004BE-C69975B0/0/0 X-Bogosity: Ham, tests=bogofilter, spamicity=0.014971, version=1.2.4 X-Spam-Flag: NO X-Spam-Status: No, score=-50.0 required=5.0 tests=ALL_TRUSTED,HTML_MESSAGE, URIBL_BLOCKED X-Spam-Checker-Version: SpamAssassin 3.4.2 on Niue.ZEDAT.FU-Berlin.DE X-Spam-Level: Subject: [Facets-of-complexity] Invitation to Monday Lecture & Colloquium - November 12th 2018 X-BeenThere: facets-of-complexity@lists.fu-berlin.de X-Mailman-Version: 2.1.29 Precedence: list List-Id: announcements of Monday lectures and other events List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 08 Nov 2018 11:19:07 -0000 This is a multi-part message in MIME format. --------------6EB16D1C3B5AC5F9FE472636 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit You are cordially invited to our Monday Lecture & Colloquium on November 12th at 14:15 h & 16:00 h at HU Berlin. *_Location_**: ** * *Humboldt-Kabinett (between House 3&4 / 1st Floor)* *[British Reading]* Humboldt-Universität zu Berlin Institut für Informatik Johann von Neumann-Haus Rudower Chaussee 25 12489 Berlin *_Time_: **Monday, November 12th - 14:15 h* *_Lecture_: Christoph Berkholz (Humboldt-Universität zu Berlin)* *_Title_: **A comparison of algebraic and semi-algebraic proof systems * *_Abstract_:* In this lecture I will give an introduction to algebraic and semi-algebraic methods for proving the unsatisfiability of systems of real polynomial equations over the Boolean hypercube. The main goal of this talk is to compare the relative strength of these approaches using methods from proof complexity. On the one hand, I will focus on the static semi-algebraic proof systems Sherali-Adams and sum-of-squares (a.k.a. Lasserre), which are based on linear and semi-definite programming relaxations. On the other hand, I will discuss polynomial calculus, which is a dynamic algebraic proof system that models Gröbner basis computations. I am going to present two recent results on the relative strength between algebraic and semi-algebraic proof systems:¹ The first result is that sum-of-squares simulates polynomial calculus: any polynomial calculus refutation of degree d can be transformed into a sum-of-squares refutation of degree 2d and only polynomial increase in size. In contrast, the second result shows that this is not the case for Sherali-Adams: there are systems of polynomial equations that have polynomial calculus refutations of degree 3 and polynomial size, but require Sherali-Adams refutations of large degree and exponential size. ¹) this work was presented at STACS 2018; a preprint is available at https://eccc.weizmann.ac.il/report/2017/154/ _*Coffee & Tea Break*_*:*_* *_* Before ***Humboldt-Kabinett (between House 3&4 / 1st Floor)* *[British Reading]* * *_Time_: **Monday, ***November 12th* - 16:00 h* *_Colloquium_: Till Fluschnik (Technische Universität Berlin) * *_Title_: Fractals for Kernelization Lower Bounds* *_Abstract_:* Kernelization is a key concept in fixed-parameter algorithmics for polynomial-time preprocessing of NP-hard problems. Herein one seeks to preprocess any instance of a parameterized problem with parameter k to an “equivalent” instance (the so-called (problem) kernel) with size upper-bounded by some function (preferably by some polynomial) in k. Ten years ago, with the development of the so-called composition technique, first NP-hard parameterized problems were proven to presumably admit no polynomial-size problem kernel. Since then the line of Research concerning "limits of kernelization" received a lot of attention. We contribute to this line and present a new technique exploiting triangle-based fractal structures (so called T-fractals) for extending the range of applicability of compositions. Our technique makes it possible to prove new no-polynomial-kernel results for a number of graph problems dealing with some sort of cuts, hereby answering an open question stated in 2009. Our T-fractals---due to their fractal structure---admit easy-to-prove useful properties exploitable for constructing compositions. They also apply for planar as well as directed variants of the basic problems and also apply to both edge and vertex-deletion problems. This is joint work with Danny Hermelin, André Nichterlein, and Rolf Niedermeier. (Journal version appeared in SIAM Journal on Discrete Mathematics 2018.) --------------6EB16D1C3B5AC5F9FE472636 Content-Type: text/html; charset=utf-8 Content-Transfer-Encoding: 8bit

You are cordially invited to our Monday Lecture & Colloquium on November 12th at 14:15 h & 16:00 h at HU Berlin.

Location:

Humboldt-Kabinett (between House 3&4 / 1st Floor) [British Reading]
Humboldt-Universität zu Berlin
Institut für Informatik
Johann von Neumann-Haus
Rudower Chaussee 25
12489 Berlin

Time: Monday, November 12th - 14:15 h

Lecture: Christoph Berkholz (Humboldt-Universität zu Berlin)

Title: A comparison of algebraic and semi-algebraic proof systems

Abstract:

In this lecture I will give an introduction to algebraic and semi-algebraic methods for proving the unsatisfiability of systems of real polynomial equations over the Boolean hypercube. The main goal of this talk is to compare the relative strength of these approaches using methods from proof complexity.
On the one hand, I will focus on the static semi-algebraic proof systems Sherali-Adams and sum-of-squares (a.k.a. Lasserre), which are based on linear and semi-definite programming relaxations. On the other hand, I will discuss polynomial calculus, which is a dynamic algebraic proof system that models Gröbner basis computations.
I am going to present two recent results on the relative strength between algebraic and semi-algebraic proof systems:¹
The first result is that sum-of-squares simulates polynomial calculus: any polynomial calculus refutation of degree d can be transformed into a sum-of-squares refutation of degree 2d and only polynomial increase in size. In contrast, the second result shows that this is not the case for Sherali-Adams: there are systems of polynomial equations that have polynomial calculus refutations of degree 3 and polynomial size, but require Sherali-Adams refutations of large degree and exponential size.

¹) this work was presented at STACS 2018; a preprint is available at https://eccc.weizmann.ac.il/report/2017/154/


Coffee & Tea Break :

Before Humboldt-Kabinett (between House 3&4 / 1st Floor) [British Reading]

Time: Monday, November 12th - 16:00 h

Colloquium: Till Fluschnik (Technische Universität Berlin)

Title: Fractals for Kernelization Lower Bounds

Abstract:

Kernelization is a key concept in fixed-parameter algorithmics for polynomial-time preprocessing of NP-hard problems. Herein one seeks to preprocess any instance of a parameterized problem with parameter k to an “equivalent” instance (the so-called (problem) kernel) with size upper-bounded by some function (preferably by some polynomial) in k. Ten years ago, with the development of the so-called composition technique, first NP-hard parameterized problems were proven to presumably admit no polynomial-size problem kernel. Since then the line of Research concerning "limits of kernelization" received a lot of attention. We contribute to this line and present a new technique exploiting triangle-based fractal structures (so called T-fractals) for extending the range of applicability of compositions. Our technique makes it possible to prove new no-polynomial-kernel results for a number of graph problems dealing with some sort of cuts, hereby answering an open question stated in 2009. Our T-fractals---due to their fractal structure---admit easy-to-prove useful properties exploitable for constructing compositions. They also apply for planar as well as directed variants of the basic problems and also apply to both edge and vertex-deletion problems. This is joint work with Danny Hermelin, André Nichterlein, and Rolf Niedermeier.
(Journal version appeared in SIAM Journal on Discrete Mathematics 2018.)
--------------6EB16D1C3B5AC5F9FE472636-- From i.brunke@inf.fu-berlin.de Thu Nov 15 14:06:23 2018 Received: from outpost1.zedat.fu-berlin.de ([130.133.4.66]) by list1.zedat.fu-berlin.de (Exim 4.85) for facets-of-complexity@lists.fu-berlin.de with esmtps (TLSv1.2:DHE-RSA-AES256-GCM-SHA384:256) (envelope-from ) id <1gNHLj-003ZQG-5p>; Thu, 15 Nov 2018 14:06:23 +0100 Received: from inpost2.zedat.fu-berlin.de ([130.133.4.69]) by outpost.zedat.fu-berlin.de (Exim 4.85) for facets-of-complexity@lists.fu-berlin.de with esmtps (TLSv1.2:DHE-RSA-AES256-GCM-SHA384:256) (envelope-from ) id <1gNHLj-002Kcy-2e>; Thu, 15 Nov 2018 14:06:23 +0100 Received: from punkt.imp.fu-berlin.de ([160.45.40.245]) by inpost2.zedat.fu-berlin.de (Exim 4.85) for facets-of-complexity@lists.fu-berlin.de with esmtpsa (TLSv1.2:AES128-SHA:128) (envelope-from ) id <1gNHLi-000KHC-Md>; Thu, 15 Nov 2018 14:06:23 +0100 From: Ita Brunke To: facets-of-complexity@lists.fu-berlin.de Message-ID: <094267fd-ddfa-91a2-30f7-964f2404a8ee@inf.fu-berlin.de> Date: Thu, 15 Nov 2018 14:06:22 +0100 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.3.0 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="------------86EBBCF3B65B9D6142037AA1" Content-Language: en-US X-Originating-IP: 160.45.40.245 X-ZEDAT-Hint: A X-purgate: clean X-purgate-type: clean X-purgate-ID: 151147::1542287183-000004BE-4EC51FC0/0/0 X-Bogosity: Ham, tests=bogofilter, spamicity=0.011713, version=1.2.4 X-Spam-Flag: NO X-Spam-Status: No, score=-50.0 required=5.0 tests=ALL_TRUSTED,HTML_MESSAGE X-Spam-Checker-Version: SpamAssassin 3.4.2 on Niue.ZEDAT.FU-Berlin.DE X-Spam-Level: Subject: [Facets-of-complexity] Invitation to Monday Lecture & Colloquium - November 19th 2018 X-BeenThere: facets-of-complexity@lists.fu-berlin.de X-Mailman-Version: 2.1.29 Precedence: list List-Id: announcements of Monday lectures and other events List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 15 Nov 2018 13:06:23 -0000 This is a multi-part message in MIME format. --------------86EBBCF3B65B9D6142037AA1 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit You are cordially invited to our Monday Lecture & Colloquium on November 19th at 14:15 h & 16:00 h at TU Berlin. *_Location_**: ** * *Room MA 041 - Ground Floor* Technische Universität Berlin Straße des 17. Juni 136 10623 Berlin *_Time_: **Monday, November 19th - 14:15 h* *_Lecture_: Jörg Rambau (Universität Bayreuth)* *_Title_: **Optimal Diplomacy * *_Abstract_:* Picture yourself in a committee numerically evaluating a scientific proposal that you find worth funding: A rating of "0" means "easily achievable but not at all innovative", whereas "1" means "very innovative but totally unachievable". In both cases, funding is not recommended. In contrast, "1/2" means "innovative and achievable", in other words: worth funding. All intermediate values are possible. Any rating that is closer to "1/2" than to "1/4" and "3/4" is considered a vote for funding. The proposal passes if 50% of the members support funding, i.e., rate the proposal between "1/2 - 1/8" and "1/2 + 1/8". Now, there are 10 meetings ahead of you. You have an idea how the opinions of the committee members develop. How should your statements look like in the meetings one through ten if you want to have eventually as many supporters of the proposal as possible? This is an instance of the "Optimal Diplomacy Problem" (ODP), introduced by Hegselmann, König, Kurz, Niemann, and Rambau in 2010, published in 2015. How do opinions interact? How is the dynamics of opinions modeled mathematically? What does it mean to "influence others" in this dynamical system? How difficult is it to find optimal diplomacies? How can one compute or at least narrow down optimal diplomacies? What happens if not all informations about committee members are known to the diplomat? In this talk we will discuss our findings, techniques, and open questions based on the arguably most influential model: the Bounded-Confidence model by Hegselmann and Krause. We draw on joint work with Andreas Deuerling, Rainer Hegselmann, Stefan König, Julia Kinkel, Sascha Kurz, and Christoph Niemann. _*Coffee & Tea Break*_*:*_* *_* **R**oom MA 316 - Third Floor***[British Reading]* * *_Time_: **Monday, ***November 19th* - 16:00 h* *_Colloquium_: Jean-Philippe Labbé (Freie Universität Berlin) * *_Title_: (At least) three hard problems behind the multiassociahedron * *_Abstract_:* The associahedron has a natural extension called the multiassociahedron. It is a vertex-decomposable simplicial sphere (in other words, a "combinatorially nice" sphere). Since at least 2003, people tried to construct simplicial polytopes, whose boundary is this simplicial complex, with limited success. In this talk, I will reveal (at least) three combinatorial "known-to-be-challenging" computational problems which should be indispensably faced to solve this problem. --------------86EBBCF3B65B9D6142037AA1 Content-Type: text/html; charset=utf-8 Content-Transfer-Encoding: 8bit

You are cordially invited to our Monday Lecture & Colloquium on November 19th at 14:15 h & 16:00 h at TU Berlin.

Location:

Room MA 041 - Ground Floor
Technische Universität Berlin
Straße des 17. Juni 136
10623 Berlin

Time: Monday, November 19th - 14:15 h

Lecture: Jörg Rambau (Universität Bayreuth)

Title: Optimal Diplomacy

Abstract:

Picture yourself in a committee numerically evaluating a scientific proposal that you find worth funding: A rating of "0" means "easily achievable but not at all innovative", whereas "1" means "very innovative but totally unachievable". In both cases, funding is not recommended. In contrast, "1/2" means "innovative and achievable", in other words: worth funding. All intermediate values are possible. Any rating that is closer to "1/2" than to "1/4" and "3/4" is considered a vote for funding. The proposal passes if 50% of the members support funding, i.e., rate the proposal between "1/2 - 1/8" and "1/2 + 1/8". Now, there are 10 meetings ahead of you. You have an idea how the opinions of the committee members develop. How should your statements look like in the meetings one through ten if you want to have eventually as many supporters of the proposal as possible? This is an instance of the "Optimal Diplomacy Problem" (ODP), introduced by Hegselmann, König, Kurz, Niemann, and Rambau in 2010, published in 2015. How do opinions interact? How is the dynamics of opinions modeled mathematically? What does it mean to "influence others" in this dynamical system? How difficult is it to find optimal diplomacies? How can one compute or at least narrow down optimal diplomacies? What happens if not all informations about committee members are known to the diplomat? In this talk we will discuss our findings, techniques, and open questions based on the arguably most influential model: the Bounded-Confidence model by Hegselmann and Krause. We draw on joint work with Andreas Deuerling, Rainer Hegselmann, Stefan König, Julia Kinkel, Sascha Kurz, and Christoph Niemann.

Coffee & Tea Break :

Room MA 316 - Third Floor [British Reading]

Time: Monday, November 19th - 16:00 h

Colloquium: Jean-Philippe Labbé (Freie Universität Berlin)

Title: (At least) three hard problems behind the multiassociahedron

Abstract:

The associahedron has a natural extension called the multiassociahedron. It is a vertex-decomposable simplicial sphere (in other words, a "combinatorially nice" sphere). Since at least 2003, people tried to construct simplicial polytopes, whose boundary is this simplicial complex, with limited success. In this talk, I will reveal (at least) three combinatorial "known-to-be-challenging" computational problems which should be indispensably faced to solve this problem.
--------------86EBBCF3B65B9D6142037AA1-- From i.brunke@inf.fu-berlin.de Tue Nov 20 16:25:21 2018 Received: from outpost1.zedat.fu-berlin.de ([130.133.4.66]) by list1.zedat.fu-berlin.de (Exim 4.85) for facets-of-complexity@lists.fu-berlin.de with esmtps (TLSv1.2:DHE-RSA-AES256-GCM-SHA384:256) (envelope-from ) id <1gP7tx-001Fwc-FY>; Tue, 20 Nov 2018 16:25:21 +0100 Received: from inpost2.zedat.fu-berlin.de ([130.133.4.69]) by outpost.zedat.fu-berlin.de (Exim 4.85) for facets-of-complexity@lists.fu-berlin.de with esmtps (TLSv1.2:DHE-RSA-AES256-GCM-SHA384:256) (envelope-from ) id <1gP7tx-003SR9-Bq>; Tue, 20 Nov 2018 16:25:21 +0100 Received: from punkt.imp.fu-berlin.de ([160.45.40.245]) by inpost2.zedat.fu-berlin.de (Exim 4.85) for facets-of-complexity@lists.fu-berlin.de with esmtpsa (TLSv1.2:AES128-SHA:128) (envelope-from ) id <1gP7tx-001aBR-3H>; Tue, 20 Nov 2018 16:25:21 +0100 From: Ita Brunke To: facets-of-complexity@lists.fu-berlin.de Message-ID: <363b9caf-c453-2b7f-75e3-26f53f3dd20b@inf.fu-berlin.de> Date: Tue, 20 Nov 2018 16:25:21 +0100 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.3.0 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="------------8AD132702276B7DB3B5F6A7A" Content-Language: en-US X-Originating-IP: 160.45.40.245 X-ZEDAT-Hint: A X-purgate: clean X-purgate-type: clean X-purgate-ID: 151147::1542727521-000004BE-9691B086/0/0 X-Bogosity: Ham, tests=bogofilter, spamicity=0.152508, version=1.2.4 X-Spam-Flag: NO X-Spam-Status: No, score=-50.0 required=5.0 tests=ALL_TRUSTED,HTML_MESSAGE X-Spam-Checker-Version: SpamAssassin 3.4.2 on Tokelau.ZEDAT.FU-Berlin.DE X-Spam-Level: Subject: [Facets-of-complexity] Invitation to Monday Lecture & Colloquium - November 26th 2018 X-BeenThere: facets-of-complexity@lists.fu-berlin.de X-Mailman-Version: 2.1.29 Precedence: list List-Id: announcements of Monday lectures and other events List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 20 Nov 2018 15:25:22 -0000 This is a multi-part message in MIME format. --------------8AD132702276B7DB3B5F6A7A Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit You are cordially invited to our Monday Lecture & Colloquium on November 26th at 14:15 h & 16:00 h at HU Berlin. *_Location_**: ** * *Humboldt-Kabinett (between House 3&4 / 1st Floor)* *[British Reading]* Humboldt-Universität zu Berlin Institut für Informatik Johann von Neumann-Haus Rudower Chaussee 25 12489 Berlin *_Time_: **Monday, November 26th - 14:15 h* *_Lecture_: Marcin Pilipczuk (University of Warsaw)* *_Title_: **The square root phenomenon: subexponential algorithms in sparse graph classes * *_Abstract_:* While most NP-hard graph problems remain NP-hard when restricted to planar graphs, they become somewhat simpler: they often admit algorithms with running time exponential in the square root of the size of the graph (or some other meaningful parameter). This behavior has been dubbed "the square root phenomenon". For many problems, such an algorithm follows from the theory of bidimensionality relying on a linear dependency on the size of the largest grid minor and treewidth of a planar graph. In recent years we have seen a number of other algorithmic techniques, significantly extending the boundary of the applicability of the "square root phenomenon". In my talk I will survey this area and highlight main algorithmic approaches. _*Coffee & Tea Break*_*:*_* *_* Before ***Humboldt-Kabinett (between House 3&4 / 1st Floor)* *[British Reading]* * *_Time_: **Monday, ***November 26th* - 16:00 h* *_Colloquium_: Sebastian Siebertz (Humboldt-Universität zu Berlin) * *_Title_: First-order interpretations of sparse graph classes* *_Abstract_:* The notions of bounded expansion and nowhere denseness capture uniform sparseness of graph classes and render various algorithmic problems that are hard in general tractable. In particular, the model-checking problem for first-order logic is fixed-parameter tractable over such graph classes. With the aim of generalizing such results to dense graphs, we introduce structurally bounded expansion and structurally nowhere dense graph classes, dfined as first-order interpretations of bounded expansion and nowhere dense graph classes. As a first step towards their algorithmic treatment, we provide a characterization of structurally bounded expansion classes via low shrubdepth decompositions, a dense analogue of low treedepth decompositions. We prove that structurally nowhere dense graph classes are vc-minimal. --------------8AD132702276B7DB3B5F6A7A Content-Type: text/html; charset=utf-8 Content-Transfer-Encoding: 8bit

You are cordially invited to our Monday Lecture & Colloquium on November 26th at 14:15 h & 16:00 h at HU Berlin.

Location:

Humboldt-Kabinett (between House 3&4 / 1st Floor) [British Reading]
Humboldt-Universität zu Berlin
Institut für Informatik
Johann von Neumann-Haus
Rudower Chaussee 25
12489 Berlin

Time: Monday, November 26th - 14:15 h

Lecture: Marcin Pilipczuk (University of Warsaw)

Title: The square root phenomenon: subexponential algorithms in sparse graph classes

Abstract:

While most NP-hard graph problems remain NP-hard when restricted to planar graphs, they become somewhat simpler: they often admit algorithms with running time exponential in the square root of the size of the graph (or some other meaningful parameter). This behavior has been dubbed "the square root phenomenon". For many problems, such an algorithm follows from the theory of bidimensionality relying on a linear dependency on the size of the largest grid minor and treewidth of a planar graph. In recent years we have seen a number of other algorithmic techniques, significantly extending the boundary of the applicability of the "square root phenomenon". In my talk I will survey this area and highlight main algorithmic approaches.

Coffee & Tea Break :

Before Humboldt-Kabinett (between House 3&4 / 1st Floor) [British Reading]

Time: Monday, November 26th - 16:00 h

Colloquium: Sebastian Siebertz (Humboldt-Universität zu Berlin)

Title: First-order interpretations of sparse graph classes

Abstract:

The notions of bounded expansion and nowhere denseness capture uniform sparseness of graph classes and render various algorithmic problems that are hard in general tractable. In particular, the model-checking problem for first-order logic is fixed-parameter tractable over such graph classes. With the aim of generalizing such results to dense graphs, we introduce structurally bounded expansion and structurally nowhere dense graph classes, dfined as first-order interpretations of bounded expansion and nowhere dense graph classes. As a first step towards their algorithmic treatment, we provide a characterization of structurally bounded expansion classes via low shrubdepth decompositions, a dense analogue of low treedepth decompositions. We prove that structurally nowhere dense graph classes are vc-minimal.
--------------8AD132702276B7DB3B5F6A7A-- From rote@inf.fu-berlin.de Mon Dec 03 11:33:21 2018 Received: from outpost1.zedat.fu-berlin.de ([130.133.4.66]) by list1.zedat.fu-berlin.de (Exim 4.85) for facets-of-complexity@lists.fu-berlin.de with esmtps (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (envelope-from ) id <1gTlXV-001UiF-GN>; Mon, 03 Dec 2018 11:33:21 +0100 Received: from inpost2.zedat.fu-berlin.de ([130.133.4.69]) by outpost.zedat.fu-berlin.de (Exim 4.85) for facets-of-complexity@lists.fu-berlin.de with esmtps (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (envelope-from ) id <1gTlXV-0018dF-Ea>; Mon, 03 Dec 2018 11:33:21 +0100 Received: from dslb-178-012-117-018.178.012.pools.vodafone-ip.de ([178.12.117.18] helo=[192.168.178.36]) by inpost2.zedat.fu-berlin.de (Exim 4.85) for facets-of-complexity@lists.fu-berlin.de with esmtpsa (TLSv1.2:AES128-SHA:128) (envelope-from ) id <1gTlXV-002pLk-5R>; Mon, 03 Dec 2018 11:33:21 +0100 From: =?UTF-8?Q?G=c3=bcnter_Rote?= To: facets-of-complexity@lists.fu-berlin.de Message-ID: <0cc13894-bf20-8f25-4d84-b08bea510df2@inf.fu-berlin.de> Date: Mon, 3 Dec 2018 11:33:16 +0100 User-Agent: Mozilla/5.0 (X11; Linux i686; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Language: en-CA Content-Transfer-Encoding: 8bit X-Originating-IP: 178.12.117.18 X-purgate: clean X-purgate-type: clean X-purgate-ID: 151147::1543833201-0005565A-EE9D5892/0/0 X-Bogosity: Ham, tests=bogofilter, spamicity=0.028377, version=1.2.4 X-Spam-Flag: NO X-Spam-Status: No, score=-50.0 required=5.0 tests=ALL_TRUSTED X-Spam-Checker-Version: SpamAssassin 3.4.2 on Tokelau.ZEDAT.FU-Berlin.DE X-Spam-Level: Subject: [Facets-of-complexity] Monday Lecture & Colloquium - Dec 3, 2018 - TODAY X-BeenThere: facets-of-complexity@lists.fu-berlin.de X-Mailman-Version: 2.1.29 Precedence: list List-Id: announcements of Monday lectures and other events List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 03 Dec 2018 10:33:22 -0000 You are cordially invited to our Monday Lecture & Colloquium on Dec 3rd at 14:15 h & 16:00 h at FU Berlin. Lecture: Monday, Dec 3rd - 14:15 h =============================================== László Kozma (Freie Universität Berlin): Self-adjusting data structures: trees and heaps =============================================== Abstract: Binary search trees (BSTs) and heaps are perhaps the simplest implementations of the dictionary and the priority queue data types. They are among the most extensively studied structures in computer science, yet, many basic questions about them remain open. What is the best strategy for updating a BST in response to queries? Is there a single strategy that is optimal for every possible scenario? Are self-adjusting trees ("splay trees", Sleator and Tarjan, 1983) optimal? In which cases can we improve upon the logarithmic worst-case cost per operation? Our understanding of heaps is even more limited. Fibonacci heaps (and their relatives) are theoretically optimal in a worst-case sense, but they perform operations outside the "pure" comparison-based heap model (in addition to being complicated in practice). Is there a simple, "self-adjusting" alternative to Fibonacci heaps? Is there, by analogy to BSTs, a heap that can adapt to regularities in the input? Are the two problems related? In my talk I will present some old and new results pertaining to this family of questions. Coffee & Tea Break Colloquium: 16:00 h =============================================================== Petr Gregor (Charles University, Prague): Incidence colorings of subquartic graphs and Cartesian products =============================================================== Abstract: Two incidences (u,e) and (v,f) of vertices u, v and edges e, f (respectively) are adjacent if u=v, or e=f, or uv is one of edges e, f. An incidence coloring of a graph G is a coloring of its incidences such that adjacent incidences have distinct colors. We show that every graph of maximal degree 4 has an incidence coloring with 7 colors. Furthermore, we present sufficient conditions for Cartesian product graphs to have incidence colorings with Delta+2 colors where Delta is the maximal degree. In particular, we confirm a conjecture of Pai et al. on incidence colorings of hypercubes. Joint work with B. Lužar and R. Soták. Location: Room 005 - Ground Floor Freie Universität Berlin Takustr. 9 14195 Berlin From i.brunke@inf.fu-berlin.de Thu Dec 06 17:03:24 2018 Received: from outpost1.zedat.fu-berlin.de ([130.133.4.66]) by list1.zedat.fu-berlin.de (Exim 4.85) for facets-of-complexity@lists.fu-berlin.de with esmtps (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (envelope-from ) id <1gUw7Y-000A9C-1D>; Thu, 06 Dec 2018 17:03:24 +0100 Received: from inpost2.zedat.fu-berlin.de ([130.133.4.69]) by outpost.zedat.fu-berlin.de (Exim 4.85) for facets-of-complexity@lists.fu-berlin.de with esmtps (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (envelope-from ) id <1gUw7X-001a1z-VF>; Thu, 06 Dec 2018 17:03:23 +0100 Received: from punkt.imp.fu-berlin.de ([160.45.40.245]) by inpost2.zedat.fu-berlin.de (Exim 4.85) for facets-of-complexity@lists.fu-berlin.de with esmtpsa (TLSv1.2:AES128-SHA:128) (envelope-from ) id <1gUw7X-002vsw-Nr>; Thu, 06 Dec 2018 17:03:23 +0100 From: Ita Brunke To: facets-of-complexity@lists.fu-berlin.de Message-ID: <59fca3af-c4c9-32df-9796-efdfcaaffd73@inf.fu-berlin.de> Date: Thu, 6 Dec 2018 17:03:23 +0100 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.3.0 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="------------0B873EBE9050253E371C2135" Content-Language: en-US X-Originating-IP: 160.45.40.245 X-ZEDAT-Hint: A X-purgate: clean X-purgate-type: clean X-purgate-ID: 151147::1544112204-0002A4D2-5A6AB7C7/0/0 X-Bogosity: Ham, tests=bogofilter, spamicity=0.318117, version=1.2.4 X-Spam-Flag: NO X-Spam-Status: No, score=-50.0 required=5.0 tests=ALL_TRUSTED,HTML_MESSAGE X-Spam-Checker-Version: SpamAssassin 3.4.2 on Palau.ZEDAT.FU-Berlin.DE X-Spam-Level: Subject: [Facets-of-complexity] Invitation to Monday Lecture & Colloquium - December 10th 2018 X-BeenThere: facets-of-complexity@lists.fu-berlin.de X-Mailman-Version: 2.1.29 Precedence: list List-Id: announcements of Monday lectures and other events List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 06 Dec 2018 16:03:24 -0000 This is a multi-part message in MIME format. --------------0B873EBE9050253E371C2135 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit You are cordially invited to our next Monday Lecture & Colloquium on December 10th at 14:15 h & 16:00 h at FU Berlin. *_Location_**: ** * *Room 005 - Ground Floor* Freie Universität Berlin Takustr. 9 14195 Berlin *_Time_: **Monday, December 10th - 14:15 h* *_Lecture_: Marijn Heule (University**of Texas, Austin)* *_Title_: Everything's Bigger in Texas: "The Largest Math Proof Ever" * *_Abstract_:* Progress in satisfiability (SAT) solving has enabled answering long-standing open questions in mathematics completely automatically resulting in clever though potentially gigantic proofs. We illustrate the success of this approach by presenting the solution of the Boolean Pythagorean triples problem. We also produced and validated a proof of the solution, which has been called the ``largest math proof ever''. The enormous size of the proof is not important. In fact a shorter proof would have been preferable. However, the size shows that automated tools combined with super computing facilitate solving bigger problems. Moreover, the proof of 200 terabytes can now be validated using highly trustworthy systems, demonstrating that we can check the correctness of proofs no matter their size. _*Coffee & Tea Break*_ *Room 134* *_Time_: **Monday, ***December 10th* - 16:00 h s.t.* *_Colloquium_: Ander Lamaison (Freie Universität Berlin**)* *_Title_: Ramsey density of infinite paths * *_Abstract_:* In a two-colouring of the edges of the complete graph on the natural numbers, what is the densest monochromatic infinite path that we can always find? We measure the density of a path by the upper asymptotic density of its vertex set. This question was first studied by Erdös and Galvin, who proved that the best density is between 2/3 and 8/9. In this talk we settle this question by proving that we can always find a monochromatic path of upper density at least (12+sqrt(8))/17=0.87226…, and constructing a two-colouring in which no denser path exists. This represents joint work with Jan Corsten, Louis DeBiasio and Richard Lang. --------------0B873EBE9050253E371C2135 Content-Type: text/html; charset=utf-8 Content-Transfer-Encoding: 8bit

You are cordially invited to our next Monday Lecture & Colloquium on December 10th at 14:15 h & 16:00 h at FU Berlin.

Location:

Room 005 - Ground Floor
Freie Universität Berlin
Takustr. 9
14195 Berlin

Time: Monday, December 10th - 14:15 h

Lecture: Marijn Heule (University of Texas, Austin)

Title: Everything's Bigger in Texas: "The Largest Math Proof Ever"

Abstract:

Progress in satisfiability (SAT) solving has enabled answering long-standing open questions in mathematics completely automatically resulting in clever though potentially gigantic proofs. We illustrate the success of this approach by presenting the solution of the Boolean Pythagorean triples problem. We also produced and validated a proof of the solution, which has been called the ``largest math proof ever''. The enormous size of the proof is not important. In fact a shorter proof would have been preferable. However, the size shows that automated tools combined with super computing facilitate solving bigger problems. Moreover, the proof of 200 terabytes can now be validated using highly trustworthy systems, demonstrating that we can check the correctness of proofs no matter their size.


Coffee & Tea Break
Room 134

Time: Monday, December 10th - 16:00 h s.t.

Colloquium: Ander Lamaison (Freie Universität Berlin)

Title: Ramsey density of infinite paths

Abstract:
In a two-colouring of the edges of the complete graph on the natural numbers, what is the densest monochromatic infinite path that we can always find? We measure the density of a path by the upper asymptotic density of its vertex set. This question was first studied by Erdös and Galvin, who proved that the best density is between 2/3 and 8/9. In this talk we settle this question by proving that we can always find a monochromatic path of upper density at least (12+sqrt(8))/17=0.87226…, and constructing a two-colouring in which no denser path exists. This represents joint work with Jan Corsten, Louis DeBiasio and Richard Lang.
--------------0B873EBE9050253E371C2135-- From rote@inf.fu-berlin.de Fri Dec 14 11:58:14 2018 Received: from outpost1.zedat.fu-berlin.de ([130.133.4.66]) by list1.zedat.fu-berlin.de (Exim 4.85) for facets-of-complexity@lists.fu-berlin.de with esmtps (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (envelope-from ) id <1gXlAb-000C2i-Q1>; Fri, 14 Dec 2018 11:58:14 +0100 Received: from inpost2.zedat.fu-berlin.de ([130.133.4.69]) by outpost.zedat.fu-berlin.de (Exim 4.85) for facets-of-complexity@lists.fu-berlin.de with esmtps (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (envelope-from ) id <1gXlAb-000ERE-Ns>; Fri, 14 Dec 2018 11:58:13 +0100 Received: from strecke.imp.fu-berlin.de ([160.45.40.209]) by inpost2.zedat.fu-berlin.de (Exim 4.85) for facets-of-complexity@lists.fu-berlin.de with esmtpsa (TLSv1.2:AES128-SHA:128) (envelope-from ) id <1gXlAb-000b3M-Hw>; Fri, 14 Dec 2018 11:58:13 +0100 References: <0cc13894-bf20-8f25-4d84-b08bea510df2@inf.fu-berlin.de> To: facets-of-complexity@lists.fu-berlin.de From: =?UTF-8?Q?G=c3=bcnter_Rote?= X-Forwarded-Message-Id: <0cc13894-bf20-8f25-4d84-b08bea510df2@inf.fu-berlin.de> Message-ID: Date: Fri, 14 Dec 2018 11:58:13 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.3.0 MIME-Version: 1.0 In-Reply-To: <0cc13894-bf20-8f25-4d84-b08bea510df2@inf.fu-berlin.de> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Originating-IP: 160.45.40.209 X-purgate: clean X-purgate-type: clean X-purgate-ID: 151147::1544785093-000901CF-BEF2C51D/0/0 X-Bogosity: Ham, tests=bogofilter, spamicity=0.030365, version=1.2.4 X-Spam-Flag: NO X-Spam-Status: No, score=-50.0 required=5.0 tests=ALL_TRUSTED X-Spam-Checker-Version: SpamAssassin 3.4.2 on Kiribati.ZEDAT.FU-Berlin.DE X-Spam-Level: Subject: [Facets-of-complexity] Monday Lecture & Colloquium - Dec 17, 2018 X-BeenThere: facets-of-complexity@lists.fu-berlin.de X-Mailman-Version: 2.1.29 Precedence: list List-Id: announcements of Monday lectures and other events List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 14 Dec 2018 10:58:14 -0000 You are invited to our Monday Lecture & Colloquium on Dec 17th at 14:15 h & 16:00 h at FU Berlin. Lecture: Monday, Dec 17th - 14:15 h =============================================== Shagnik Das (Freie Universität Berlin): Randomly perturbed Ramsey problems =============================================== Abstract: The combinatorial properties much-loved Erdős-Rényi random graph G(n,p), which has n vertices and whose edges are present independently with probability p, have been comprehensively studied in the decades since its introduction. In recent years, much research has been devoted to the randomly perturbed graph model, introduced in 2003 by Bohman, Frieze and Martin. In this talk we shall present and motivate this new model of random graphs, and then focus on the Ramsey properties of these randomly perturbed graphs. More precisely, given a pair of graphs (F,H), we ask how many random edges must be added to a dense graph G to ensure that any two-colouring of the edges of the perturbed graph has either a red copy of F or a blue copy of G. This question was first studied in 2006 by Krivelevich, Sudakov and Tetali, who answered it in the case of F being a triangle and H being a clique. We generalise these results, considering pairs of larger cliques, and, should the audience be willing (but even otherwise), shall take a quick look at some of the ideas required in our proofs. This is joint work with Andrew Treglown (Birmingham). Coffee & Tea Break Colloquium: 16:00 h =============================================================== Marie Brandenburg (Freie Universität Berlin): Product-Mix Auctions, Competitive Equilibrium and Lattice Polytopes =============================================================== Abstract: In 2007, when the credit crisis began, the Bank of England approached the economist Paul Klemperer with the need of a new auction design that would enable them to give liquidity to all banks in an economically efficient way. Since then, Klemperer’s Product-Mix Auction design became more and more relevant, with particular interest in when competitive equilibrium exists, that is, when a set of (indivisible) goods can be split such that exactly one bid of each bidder is fulfilled. Originally being a question of economics, this can be translated into a question of specific lattice polytopes that rely on underlying graphs. I will present the Product-Mix Auction setting, the translation to polytopes and first results on when competitive equilibrium exists. Location: Room 005 - Ground Floor Freie Universität Berlin Takustr. 9 14195 Berlin From rote@inf.fu-berlin.de Sun Dec 30 01:29:47 2018 Received: from outpost1.zedat.fu-berlin.de ([130.133.4.66]) by list1.zedat.fu-berlin.de (Exim 4.85) for facets-of-complexity@lists.fu-berlin.de with esmtps (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (envelope-from ) id <1gdOzD-002YMl-Gx>; Sun, 30 Dec 2018 01:29:47 +0100 Received: from inpost2.zedat.fu-berlin.de ([130.133.4.69]) by outpost.zedat.fu-berlin.de (Exim 4.85) for facets-of-complexity@lists.fu-berlin.de with esmtps (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (envelope-from ) id <1gdOzD-0000ns-EY>; Sun, 30 Dec 2018 01:29:47 +0100 Received: from z0ec3.pia.fu-berlin.de ([87.77.14.195]) by inpost2.zedat.fu-berlin.de (Exim 4.85) for facets-of-complexity@lists.fu-berlin.de with esmtpsa (TLSv1.2:DHE-RSA-AES128-SHA:128) (envelope-from ) id <1gdOzD-002nCv-2X>; Sun, 30 Dec 2018 01:29:47 +0100 From: =?UTF-8?Q?G=c3=bcnter_Rote?= To: facets-of-complexity@lists.fu-berlin.de References: Message-ID: <7f002bd3-b362-9102-de49-adeb94711989@inf.fu-berlin.de> Date: Sun, 30 Dec 2018 01:29:54 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Originating-IP: 87.77.14.195 X-purgate: clean X-purgate-type: clean X-purgate-ID: 151147::1546129787-0008B5E6-634BFDB2/0/0 X-Bogosity: Ham, tests=bogofilter, spamicity=0.125440, version=1.2.4 X-Spam-Flag: NO X-Spam-Status: No, score=-50.0 required=5.0 tests=ALL_TRUSTED X-Spam-Checker-Version: SpamAssassin 3.4.2 on Kiribati.ZEDAT.FU-Berlin.DE X-Spam-Level: Subject: [Facets-of-complexity] New Year's Monday Lecture & Colloquium - Jan 7, 2019 at FU X-BeenThere: facets-of-complexity@lists.fu-berlin.de X-Mailman-Version: 2.1.29 Precedence: list List-Id: announcements of Monday lectures and other events List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 30 Dec 2018 00:29:48 -0000 You are invited to our Monday Lecture & Colloquium on Jan 7th, 2019 at 14:15 h & 16:00 h at FU Berlin. Lecture: Monday, January 7th - 14:15 h =============================================== Péter Pál Pach (Budapest University of Technology and Economics): The polynomial method and the cap set problem =============================================== Abstract: In this talk we will look at a new variant of the polynomial method which was first used to prove that sets avoiding 3-term arithmetic progressions in groups like Z_4^n (Croot, Lev and myself) and Z_3^n (Ellenberg and Gijswijt) are exponentially small (compared to the size of the group). We will discuss lower and upper bounds for the size of the extremal subsets, including some recent bounds found by Elsholtz and myself. We will also mention some further applications of the method, for instance, the solution of the Erdős-Szemerédi sunflower conjecture. Coffee & Tea Break: Room 134 Colloquium: 16:00 h =============================================================== Ardalan Khazraei (Bonn): Cost-distance Steiner trees =============================================================== Abstract: In the well-known Steiner Tree Problem, the objective is to connect a set of terminals at the least total cost. We can further constrain the problem by specifying upper bounds for the distance of each terminal to a chosen root terminal. Further, using the Lagrangian relaxation of this restriction, we can penalize large distances in the objective function rather than applying strict distance constraints. We arrive at a special case of the so-called Cost-Distance Steiner Tree Problem in which we have a single weight function on the edges. In this talk, I will present several results from my master's thesis that concern the Cost-Distance Steiner Tree Problem. The NP-hardness of the Cost-Distance Steiner Tree Problem trivially follows from the fact that the regular Steiner Tree Problem is the special case where we set demand weights (Lagrange multipliers) of the terminals to zero. I therefore proceed to prove that the problem remains NP-hard in three restricted cases that do not contain the regular Steiner Tree Problem as a special case anymore. Then I improve on a previous constant-factor approximation for the single-weighted case by using a hybrid method of an approximate Steiner tree with a shortest path tree replacing sections of the tree where path segments are used by many terminals with demand weights summing to higher than a tunable threshold. I also use a similar approach to extend Arora's dynamic programming method for the two-dimensional geometric Steiner Tree Problem to the case with the penalizing terms in the objective function. Location: Room 005 - Ground Floor Freie Universität Berlin Takustr. 9 14195 Berlin