The role of communication in computational complexity.

Nathan Segerlind
Department of Computer Science, Portland State University March

Abstract: There are many mathematical problems that people want to solve with computers- gathering statistics from databases, verifying hardware and software designs, solving systems of equations, et cetera. For some of these problems, there are known to be efficient algorithms. For the others, no efficient algorithms are known, and for many of these tasks, it is believed that all algorithms for solving these problems are inherently inefficient. Identifying these hard problems and rigorously and quantitatively establishing just how hard they are is the central task in computational complexity.

In this survey talk, I will discuss one of the most successful tools in computational complexity: Communication complexity—the study of how many bits must be broadcast when the inputs to a function are split up between multiple players and the players must communicate to arrive at the answer.

The talk will discuss how communication complexity provides a bridge between computing and combinatorics, some applications to establishing limitations for algorithmic techniques in streaming algorithms, circuit synthesis, and integer optimization, and hopefully prove a simple foundational result or two, and hit on some open questions.

Prerequisites should be pretty minimal.


Nathan Segerlind is visiting/adjunct professor at Portland State University. He received a PhD in 2003 in computer science from UC San Diego under the direction of Sam Buss and Russell Impagliazzo. The dissertation was awarded the Association for Symbolic Logic Sacks Prize for Outstanding Doctoral Dissertation as well as the European Association of Computer Science Logic Ackermann Prize for Outstanding doctoral dissertation. He has held postdoctoral appointments at the Institute for Advanced Study and the University of Washington. He is interested in the theory of computation, logic, combinatorics and algorithms. Several of Nathan's current and recent projects make use of communication complexity.