Department of Computer Science | Institute of Theoretical Computer Science | CADMO

Theory of Combinatorial Algorithms

Prof. Emo Welzl and Prof. Bernd Gärtner

Mittagsseminar (in cooperation with M. Ghaffari, A. Steger and B. Sudakov)

Mittagsseminar Talk Information

Date and Time: Friday, November 22, 2013, 12:15 pm

Duration: 30 minutes

Location: CAB G11

Speaker: Uli Wagner (Institute of Science and Technology Austria)

Can a balloon be shrunk to a point in the presence of obstacles? --- An Introduction to Computational Homotopy Theory

A classical result on the computational complexity of topological problems is that there is no algorithm to decide whether a given closed loop inside a given "shape" can be contracted to a single point without ever leaving the shape (more formally, it is undecidable whether a given element of the fundamental group of a given space is trivial).

In this talk, we will give a gentle introduction to a family of algorithmic questions of the same flavor, namely concerning the classification, up to continuous deformation, of continuous maps from one space into another. It turns out that for these questions there is a sharp "phase transition" between polynomiality and undecidability: on the one hand, under suitable hypothesis these questions can be solved in polynomial time, but if these hypotheses are slightly relaxed, the questions become undecidable.

This will be a survey on recent joint with Čadek, Krčál, Matoušek, Sergeraert, and Vokřínek.

Upcoming talks     |     All previous talks     |     Talks by speaker     |     Upcoming talks in iCal format (beta version!)

Previous talks by year:   2018  2017  2016  2015  2014  2013  2012  2011  2010  2009  2008  2007  2006  2005  2004  2003  2002  2001  2000  1999  1998  1997  1996  

Information for students and suggested topics for student talks

Automatic MiSe System Software Version 1.4803M   |   admin login