Theory of Combinatorial Algorithms
Teaching and Research Group Emo Welzl
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Personnel, Guests, Grants, Publications, Lectures, Courses, Workshops, Dissertations, Master Theses, Bachelor Theses, Miscellaneous, Software

Personnel

Professors
Gärtner, Bernd
Fukuda, Komei
Matoušek, Jiří
Welzl, Emo

Research Associates and Ph.D. Students
Hertli, Timon
Hoffmann, Michael, Dr.
Kusters, Vincent
Stich, Sebastian
Szedlák, May
Thomas, Antonis
Tyagi, Hemant
Wettstein, Manuel

Administration
Salow, Andrea
Guests
Grants

Redundancy in Linear and Neuromuscular Systems
(Financed by the Swiss National Science Foundation).
Understanding and removing redundancy in a given data to improve
computational efficiency or discover its fundamental structure is a
universal problem in science and engineering, as the data or the
mathematical model to be analyzed in any realistic situation often
contains redundant information that is implied by the rest.
This research project has two intertwined goals, one of them
theoretical, the other one driven by a concrete application. On the
theoretical level, we want to understand the structure of
redundancy and the complexity of redundancy removal in
explicitly or implicitly given linear and more abstract systems. Here
we strongly build on our expertise in computational geometry as well
as combinatorial optimization.
On the application side, we want to compute redundancy and
assess the role of redundancy in neuromuscular control, a field
that is trying to understand how the nervous system is selecting and
implementing specific muscle commands that meet the constraints of
specific tasks. This part of the project will be performed in close
collaboration with Francisco ValeroCuevas. He pioneered in modeling
the interplay of various muscles in terms of zonotopes whose
internal structure determines the possible tasks that the muscles
under consideration can achieve together.
Contact: B. Gärtner,
K. Fukuda

Simultaneous Embeddings
(Financed by the Swiss National Science Foundation).
We use the term simultaneous (geometric) embedding to refer to any kind of problem in
which two or more graphs are to be embedded simultaneously, usually subject to certain constraints.
One reason for the strong interest in simultaneous embeddings lies in
a wealth of applications in areas such as bioinformatics, network
analysis, and software engineering. For instance, in order to compare
two phylogenetic trees one would like to have a "nice" simultaneous
drawing of two trees sharing the same set of leaves, socalled tanglegrams. More generally, simultaneous embeddings come into play whenever large or dynamically changing graphs are to be visualized. Given a large graph, only part of it can be shown at a time with a sufficient level of detail. When browsing from one such part to a neighboring one, it is desirable to have a certain overlap that is common to both parts and drawn the same way for both parts. In this way, the user can maintain her mental map and
more easily keep track of her current location in the graph. In the
context of dynamic graphs, a simultaneous drawing for several
instances of the graph at different timesteps allows to visually
examine the differences in order to, for instance, draw conclusions
regarding the capacity utilization of a network.
Beyond these motivating applications the study of simultaneous
embeddings revealed a rich collection of interesting and challenging
combinatorial and algorithmic problems, many of which are still far from
being solved. The goal of this project is, on one hand, to gain
more insights into some of these problems and, on the other hand, to
develop new models in order to address some shortcomings of the
existing settings studied so far.
The project will be carried out as an international collaboration within the collaborative research project
"GraDr: Graph Drawings and Representations", which comprises altogether 12 partners from seven European countries.
Contact: M. Hoffmann, V. Kusters
Publications

Books

Journals (with refereeing)
O. Aichholzer, T. Hackl, M. Hoffmann, A. Pilz, G. Rote, B. Speckmann, B. Vogtenhuber,
Plane Graphs with Parity Constraints,
Graphs and Combinatorics, 30:1 (2014), 4769.
A. Baertschi, S. Suri,
Conflictfree chromatic art gallery coverage,
Algorithmica 68:1 (2014), 265283.
B. Bukh, J. Matoušek,
ErdősSzekerestype statements: Ramsey function and decidability in dimension 1,
Duke Mathematical Journal (2013), to appear.
M. Čadek, M. Krčál, J. Matoušek, L. Vokřínek, U. Wagner,
Extendability of continuous maps is undecidable,
Discrete & Computational Geometry (2013), to appear.
M. Čadek, M. Krčál, J. Matoušek, F. Sergeraert, L. Vokřínek, U. Wagner,
Computing all maps into a sphere,
Journal of the ACM (2013), to appear.
J. Foniok, B. Gärtner, L. Klaus, M. Sprecher,
Counting UniqueSink Orientations,
Discrete Applied Mathematics
163:2 (2014), 155164.
F. Frati, J. Gudmundsson, E. Welzl,
On the Number of Upward Planar Orientations of Maximal Planar Graphs,
Theoretical Computer Science
(2014), to appear.
T. Hertli,
3SAT Faster and Simpler  UniqueSAT Bounds for PPSZ Hold in General,
SIAM Journal of Computing (2013), to appear.
M. Hoffmann and Cs.D. Tóth,
VertexColored Encompassing Graphs
Graphs and Combinatorics (2013), to appear.
J. Matoušek,
Nearoptimal separators in string graphs,
Combinatorics, Probability and Computing, 23:1 (2014), 135139.
J. Matoušek, U. Wagner,
On Gromov's method of selecting heavily covered points,
Discrete and Computational Geometry (2012), to appear.
H. Tyagi, V. Cevher,
Learning nonparametric basis independent models from point queries via lowrank methods,
Applied and Computational Harmonic Analysis (2014), to appear.

Conference Proceedings (with selection process)
I. Bárány, J. Matoušek, A. Por,
Curves in R^{d} intersecting every hyperplane at most d+1 times,
Proc. 30th Annual ACM Symposium on Computational Geometry (SoCG) (2014), to appear.
M. Elias, J. Matoušek, E. RoldánPensado, Z. Safernová,
Lower bounds on geometric Ramsey functions,
Proc. 30th Annual ACM Symposium on Computational Geometry (SoCG) (2014), to appear.
A. Francke, Cs.D. Tóth,
A Census of Plane Graphs with Polyline Edges,
Proc. 30th Annual ACM Symposium on Computational Geometry (SoCG) (2014), to appear.
B. Gärtner,
Sampling with Removal in LPtype Problems,
Proc. 30th Annual ACM Symposium on Computational Geometry (SoCG) (2014), to appear.
B. Gärtner, H. Tyagi,
Continuum armed bandit problem of few variables in high dimensions,
11th Workshop on Approximation and Online Algorithms (WAOA) (2013), to appear.
X. Goaoc, J. Matoušek, P. Paták, Z. Safernová,
Simplifying inclusionexclusion formulas,
European Conference on Combinatorics, Graph Theory and Applications (Eurocomb) (2013), to appear.
A. Gundert, M. Szedlák,
Higher Dimensional Discrete Cheeger Inequalities,
Proc. 30th Annual ACM Symposium on Computational Geometry (SoCG) (2014), to appear.
T.Hertli,
Breaking the PPSZ Barrier for Unique 3SAT,
41st International Colloquium on Automata, Languages and Programming (ICALP) (2014), to appear.
J. Matoušek, E. Sedgwick, M. Tancer, U. Wagner,
Embeddability in the 3sphere is decidable,
Proc. 30th Annual ACM Symposium on Computational Geometry (SoCG) (2014), to appear.
M. Wettstein,
Counting and Enumerating Crossingfree Geometric Graphs,
Proc. 30th Annual ACM Symposium on Computational Geometry (SoCG) (2014), to appear.

Other (including submitted work)
M. Čadek, M. Krčál, J. Matoušek, L. Vokřínek, U. Wagner,
Polynomialtime computation of homotopy groups and Postnikov systems in fixed dimension,
(2012), submitted.
D. Clemens, H. Gebauer, A. Liebenau,
The random graph intuition for the tournament game, (2013), submitted.
K. Fukuda, L. Klaus, H. Miyata,
Enumeration of PLCPorientations of the 4cube,
(2013), submitted.
B. Gärtner, C. Müller, S. Stich,
Variable Metric Random Pursuit,
(2012), submitted.
M. Hoffmann, V. Kusters, T. Miltzow,
Separating Balls with a Hyperplane,
Abstracts of the 30th European Workshop on Computational Geometry (EuroCG), EinGedi, Israel (2014).
V. Kusters, B. Speckmann,
Characterizing Graphs With A Sliceable Rectangular Dual,
(2013), submitted.
A. Thomas, J. van Leeuwen,
Pure Nash Equilibria in Graphical Games and Treewidth,
(2013), submitted.
H. Tyagi, S. Stich, B. Gärtner,
On two continuum armed bandit problems in high dimensions,
(2014), submitted.
H. Tyagi, S. Stich, B. Gärtner,
Stochastic continuum armed bandit problem of few linear parameters in high dimensions,
(2014).
Lectures
T. HERTLI
"Breaking the PPSZ Barrier for Unique 3SAT", CSE Theory Seminar, UC San Diego, USA (Jan 27, 2014).
V. KUSTERS
"Planar Packing of Binary Trees",
EuroGIGA Final Conference, Freie Universität Berlin, Germany (Feb 18, 2014).
S. STICH
"Probabilistic Estimate Sequences",
TAO reserach seminar, INRIA Saclay,
ÎledeFrance, France (Mar 25, 2014).
"Probabilistic Estimate Sequences",
8th workshop on Theory of Randomized Search Heuristics (ThRaSH 2014)
Jena, Germany (Apr 4, 2014).
E. WELZL
"When Conflicting Constraints can be Resolved  the Local Lemma and Satisfiability ",
The Institute Colloquium, Institute of Science and Technology (IST Austria),
Klosterneuburg, Maria Gugging, Austria (Jan 13, 2014).
"The Counting of CrossingFree Geometric Graphs  Algorithms and Combinatorics",
PreWorkshop (WALCOM) School on Algorithms and Combinatorics,
IIT Chennai, India (Feb 10, 2014).
M. WETTSTEIN
"Counting and Enumerating Crossingfree Perfect Matchings",
EuroGIGA Final Conference, Freie Universität Berlin, Germany (Feb 21, 2014).
Courses and Seminars
Spring 14

Optimization and Applications Seminar,
B. Gärtner, D. Klatte, J. Lygeros, M. Morari, K. Schmedders, R. Smith, R. Weismantel, R. Zenklusen;
(K Mo1618 HG G19.1).

Polyhedral Computation,
K. Fukuda; (VL Tu1517 HG E1.1, UE Tu1718 HG E1.1),
contact assistant: May Szedlák.

Polynomials,
J. Matoušek; E. Welzl;
(VL Mo1012 CAB G57, UE Mo 1314 CAB G57),
contact assistant: Vincent Kusters.

Satisfiability of Boolean Formulas  Combinatorics and Algorithms,
E. Welzl;
(VL Tu1012 CAB G51, Th910 CAB G59, UE Fr1012 CAB G51, [+1A]),
contact assistant: Timon Hertli.

Seminar der Theoretischen Informatik (Mittagsseminar),
B. Gärtner, M. Hoffmann, J. Lengler, A. Steger, B. Sudakov, E. Welzl;
(SE Tu1213 CAB G51, Th1213 CAB G51).

Seminar: Wie funktioniert Forschung? Algorithmen und Kombinatorik,
B. Gärtner, J. Matoušek; A. Steger, E. Welzl, P. Widmayer;
(SE Tu1517 CAB G15.2).
Fall 13

Algorithms Lab,
A. Steger, E. Welzl, P. Widmayer;
(VL We1719 CAB G61, UE Mo1719, [+1A]),
contact email: algolab@lists.inf.ethz.ch.

Algorithms, Probability, and Computing,
E. Welzl, T. Holenstein, U. Maurer, A. Steger, P. Widmayer;
(VL Mo1315 CAB G51, Tu1416 CAB G51; UE We1315 CAB G56, We1618 CAB G52 [+1A]),
contact assistant: Vincent Kusters.

Algorithms, Probability, and Computing (honours parts),
A. Steger, T. Holenstein, U. Maurer, E. Welzl, P. Widmayer
(UE We1516 CAB G52),
contact assistant: Timon Hertli.

Computational Geometry,
B. Gärtner, M. Hoffmann, E. Welzl;
(VL Tu1112 CAB G57, Th1314 CAB G51, UE Th1416 CAB G51, [+1A]),
contact assistant: Anna Gundert.

Diskrete Mathematik (DITET),
A. Steger, E. Welzl;
(VL Mo1012 HG E1.1, UE Fr1012 biweekly)
contact assistant: Johannes Lengler.

Informatik (DMATH, DPHYS),
B. Gärtner;
(VL Tu1315 ML D28/E12, UE Tu1517),
contact assistant: Sebastian Stich.

Theory of Computing (Theoretische Informatik),
J. Hromkovic, E. Welzl;
(VL Tu810 CAB G61, Fr810 CAB G61, UE We1315, UE Th1618)

Seminar Computational Geometry and Graph Drawing,
B. Gärtner, M. Hoffmann, E. Welzl;
(SE Fr1315 CAB G15.2).

Seminar in Combinatorics: Theory of Oriented Matroids,
K. Fukuda;
(SE Tu1012 HG E33.3).

Seminar on Optimization and Applications,
R. Weismantel, B. Gärtner, D. Klatte, J. Lygeros, M. Morari, K. Schmedders, R. Smith;
(K Mo1618 HG G19.1).

Seminar SAT,
E. Welzl; contact assistant: Timon Hertli.
(SE Fr1012 CAB G57).

Seminar der Theoretischen Informatik (Mittagsseminar),
A. Steger, E. Welzl, B. Gärtner, M. Hoffmann, J. Lengler;
(SE Tu1213 CAB G51, Th1213 CAB G51).
Organization of Workshops etc.

12th Gremo Workshop on Open Problems 2014,
Val Sinestra (GR), Switzerland,
Jun 30  Jul 4, 2014,
(Michael Hoffmann).

International Workshop on Algorithms and Computation (WALCOM 2014) PreWorkshop School on Algorithms and Combinatorics,
Indian Institute of Technology, Madras, India,
Feb 13  15, 2014,
(John Augustine, Subir Ghosh, Emo Welzl, B. V. Raghavendra Rao, Swami Sarvottamananda, Partha Goswami).

JapaneseSwiss Workshop on Combinatorics and Computational Geometry
University of Tokyo, Japan, Jun 4  6, 2014, (Komei Fukuda).
Dissertations
Master Theses

Isabelle Hurbain,
Towards a Derandomization of the PPSZ Algorithm for Multiple Satisfying Assignments,
Advisor: Timon Hertli / 31.3.2014
Bachelor and Semester Theses / Internship Projects

Stephan Ammann,
Draw an outerplanar graph and a matching at the same time,
Advisors: Michael Hoffmann, Vincent Kusters / start in February 2014

Luca Eggemann,
A View of Triangulations as Maximal Cliques,
Advisor: Emo Welzl / to be completed

Patrick Schnider,
Shortest Paths in Disk Coverings,
Advisors: Michael Hoffmann, Torsten Mütze / to be completed
Miscellaneous
K. FUKUDA
Editorial Board Member of
European J. Combinatorics, Computational Geometry: Theory and Applications,
Applied Mathematics Research eXpress.
B. GÄRTNER
Mitglied im Ausbildungs und Beratungszentrum für Informatikunterricht ABZ und im Kinderlabor.
Mobilitätsberater des Departements Informatik
T. HERTLI
Teach. Assistance Coordinator.
Teach. Assistance Satisfiability of Boolean Formulas  Combinatorics and Algorithms (DINFK) (Spring 14).
M. HOFFMANN
Informatik Koordinator.
Member of the CGAL Editorial Board.
Program committee member of
V. KUSTERS
Coordinator Mittagsseminar.
Teach. Assistance Polynomials (DINFK) (Spring 14).
J. MATOUŠEK
Elected member of the
Editorial Board member of

Commentationes Mathematicae Universitatis Carolinae,
(I. Netuka, Ed.), Charles University, Prague.

Contributions to Discrete Mathematics,
(K. Bezdek, N. Sauer, H. Williams, Eds.), University of Calgary, Canada (electronic journal).

Discrete and Computational Geometry,
(J. Goodman & R. Pollack, Eds.),
Springer Verlag.

Order,
(D. Duffus, Ed.),
Springer Verlag.

Random Structures and Algorithm,
(M. Karonski, N. Alon, A. Rucinski, Eds.),
Wiley Periodicals, Inc.

Theory of Computing,
(L. Babai, Ed.),
University of Chicago, USA (electronic journal).
Program committee member of
S. STICH
Webmaster wwwgremo.
Program committee member of
M. SZEDLÁK
Teach. Assistance Polyhedral Computation (DMATH) (Spring 14).
H. TYAGI
Teach. Assistance Data Mining: Learning from Large Data Sets (DINFK) (Spring 14).
E. WELZL
Member of the board (deputy head) of the Department of Computer Science, ETH Zurich.
Editorial/Advisory Board member of

ACM Transactions on Computation Theory,
(Lance Fortnow, Ed.), ACM.

Computational Geometry  Theory and Applications,
(K. Mehlhorn & J.R. Sack, Eds.),
Elsevier Science Publishers.

Discrete and Computational Geometry,
(J. Goodman & R. Pollack, Eds.),
Springer Verlag.

EATCS Monographs in Theoretical Computer Science,
(M. Henzinger, J. Hromkovič, M. Nielsen, G. Rozenberg, A. Salomaa, Eds.),
Springer Verlag.

EATCS Texts in Theoretical Computer Science,
(M. Henzinger, J. Hromkovič, M. Nielsen, G. Rozenberg, A. Salomaa, Eds.),
Springer Verlag.

Journal for Universal Computer Science,
(H. Maurer, Ed.),
Springer Verlag (electronic journal).

Mathematik Kompakt,
(M. Brokate, H.W. Engl, K.H. Hoffmann, G. Kersting, G. Stroth, E. Welzl, Eds.),
Birkhäuser Verlag.
Member (chair, contact person) of selection committees for

Assistant Professor of Plant Cell and Developmental Biology/PlantMicrobial Interactions,
Department of Biology, ETH Zurich, (chair).

Professor of Applied Mathematics,
Department of Mathematics, ETH Zurich, (chair).

Professor of Biological Systems Theory,
Department of Biosystems Science and Engineering, ETH Zurich, (chair).

Professor of Computer Science,
Computer Science Department, Ecole normale superieure (ENS), Paris, France.

Professor of Mathematics,
Department of Mathematics, ETH Zurich.

Professor / Assistant Professor (Tenure Track) of Networked Systems,
Department of Information Technology and Electrical Engineering, ETH Zurich.
Member of the
Program committee member of

14th Scandinavian Symposium and Workshops on Algorithm Theory (SWAT `14),
Copenhagen, Denmark (July 24, 2014).
Member of ETH Quality Audit Preparation Chapter Review Group "Personal".
Delegierter für Professorenwahlen an der ETH Zürich.
Software
