Meetings

Topics

Selected Papers

• Computers program themselves
  Whether the Olivanova Model Execution Machine can fulfill its expectations is not yet clear. From a theoretical point of view, however, Marcus Hutter has presented an algorithm in 2000 that can provably solve every problem when given a functional specification of it. Moreover, his HSEARCH algorithm requires asymptotically at most a constant factor more time than any other algorithm for the given problem. Under certain, weak assumptions one can even reach a factor of 5!
• Theory of adventure games
  Among the adventure games are well-known games such as Monkey Island, Space Quest, King's Quest, and Leisure Suit Larry as well as classics such as The Dallas Quest or /usr/games/adventure under Unix. Brauer, Holzer, Koenig, and Schwoon have been able to come up with a nice classification of these games. It illustrates the perhaps otherwise quite dry area of formal languages and Chomsky hierarchy in an amusing way and implies results about the hardness of solving adventures games.
• C++ parsers are universal
  Like all practical programming languages, C++ is context-free, i.e. it can be parsed in O(n^3) steps (when ignoring the type-checking). To identify a correct C++ program under consideration of type-checking, however, is Turing-complete. Surprisingly, Boehme and Manthey have shown that already during the compilation, every partially recursive function can be computed.
• Buechi automata are closed under complement
  That a class of languages that can be accepted by a non-deterministic finite automaton (NFA) is closed under complement can be shown by transforming the NFA into an equivalent DFA. For languages of infinite words (so-called w-regular languages), however, this proof method cannot be used any more. Buechi showed in 1960 that the class of w-regular languages is nevertheless closed under complement. Here, Ramsey's Theorem for infinite graphs plays a crucial role.
• On the stretch factor of planar geometric path systems
  Suppose one wants to go from A to B. Their distance (when traveling through the air) may be x, but because of the way the streets are set up, one usually has to make a detour of length dx. Certainly, d should be as small as possible. If A and B are arbitrary nodes in a geometric graph, then this minimization problem leads to the well-known spanners. A spanner aims to keep the detour for any pair of nodes as small as possible (for example, within a constant factor of their Euclidean distance). But spanners are not planar in general. In a celebrated work, Icking et al have shown upper and lower bounds for this problems concerning the detour value (or stretch factor) d and uses a lot of interesting geometry for this.
• Quantum time-space tradeoffs for sorting
  While it is known that a quantum algorithm based on comparisons alone cannot outperform classical sorting algorithms by more than a constant factor in time complexity, this is wrong in a space bounded setting. For sequential computers the time-space tradeoff for sorting is well known to be T*S = Omega(n^2), but Klauck has shown that for quantum computers this tradeoff is only T*S = Omega(n^3/2).
• Zero-knowledge proof systems
  How can one prove a fact without revealing the fact itself? In his award-winning PhD thesis, Spielman has shown how it is possible to reveal every detail of the proof, yet the proved facts are kept secret.
• Microbial gene identification using interpolated Markov models
  Usually, one uses pattern matching methods for identifying genes. A paper by Salzberg, Delcher, Kasif, and White describes how Markov chains can be used for the identification of genes in microbial genomes.
• More topics are available on request.