Time+Place: | Monday 22/12/2014 11:00 Room 337-8 Taub Bld. |

Title: | Advances in Traffic Engineering and Discrepancy |

Speaker: | Roy Schwartz - CS-Lecture - REVISED - NOTE UNUSUAL DAY AND TIME http://www.cs.princeton.edu/~roysch/ |

Affiliation: | Department of Computer Science, Princeton University. |

Host: | Seffi Naor |

I will discuss two recent works: 1. Long running transfers in wide area networks are usually time critical, as delays might impact service quality, affect customer revenue, and increase costs incurred by waste of resources. Current traffic engineering systems fall short as they do not provide pre-facto guarantees on such long running transfers. I will present an online traffic engineering system that provides pre-facto guarantees while maximizing both fairness and network utility. The system is based on theoretical algorithmic techniques for solving packing and covering linear programs, and can quickly handle an evolving linear program containing up to millions of variables and constraints. 2. Combinatorial discrepancy is a basic problem in computer science and combinatorics, that has applications in diverse areas such as: computational geometry, complexity theory, Monte-Carlo simulation, number theory and more. Given a family of subsets S_1,\ldots,S_n of a universe N of size n, the goal is to color the elements of N by one of two colors {-1,+1} such that each set is colored as evenly as possible. Spencer's well known theorem asserts that this can be done while keeping the absolute value of the sum of the colors of every set to be O(\sqrt{n}). Known proofs, algorithmic and existential, recursively construct "partial colorings", which assign colors only to half the universe N. Unfortunately, this approach fails to provide tight guarantees to other important discrepancy problem, e.g., the Beck-Fiala and Koml\'os conjectures. Therefore, it has been an open question to find new techniques that avoid partial colorings. In this work I will present the first algorithm that directly computes a full coloring. The algorithm is based on a geometric perspective and in its core is the analysis of ellipsoids contained in polytopes. Short Bio: Roy Schwartz is currently a postdoctoral research associate at the Department of Computer Science in Princeton University. Formerly, he was a postdoctoral researcher at the Theory Group at Microsoft Research. Roy did his Ph.D. at the Technion under the supervision of Prof. Seffi Naor. His research focuses on the design and analysis of algorithms and combinatorial optimization, including: approximation algorithms and coping with NP-hardness, the geometry of metric spaces and its applications, submodular optimization, and randomized algorithms. A special emphasis is given on the combination of the above with probability and stochastic processes, continuous optimization and combinatorics. Roy's work deals both with fundamental algorithmic problems as well as applications that arise in other settings such as networking, scheduling, and machine learning.