Virginia Williams (Theory Seminar W12)

williams.jpgMultiplying matrices faster
Virginia Vassilevska Williams
University of California, Berkeley
Wednesday, March 21st, 2012, 11:00 am
EBU3B, Room 1202

Matrix multiplication is used in a large variety of applications throughout science and engineering. It is a bottleneck for many important algorithms: for standard linear algebra problems such as solving linear systems and matrix inversion, but also for many algorithms that, on the face of it, may have nothing to do with matrices. Developing better matrix multiplication algorithms is of immense interest.

In 1969 Strassen showed that the naive algorithm for multiplying matrices is not optimal, presenting an ingenious recursive algorithm. This spawned a long line of active research on the theory of matrix multiplication algorithms. In a seminal paper from 1987, Coppersmith and Winograd designed an algorithm that can multiply two n by n matrices using O(n^{2.376}) arithmetic operations. This algorithm has remained the theoretically fastest approach for matrix multiplication for 24 years.

We have recently been able to design an algorithm that multiplies n by n matrices and uses at most O(n^{2.373}) arithmetic operations, thus improving the Coppersmith-Winograd running time. The improvement is based on a recursive application of the original Coppersmith-Winograd construction, together with a general theorem that reduces the final search for the best algorithm to solving a nonlinear constraint program. The analysis is then done by numerically solving this program. In this talk, we will give intuition for the problem and highlight the key ideas needed to obtain the improvement.
Short biography
Virginia Vassilevska Williams is currently a research associate at the computer science department at Stanford University and an assistant research engineer at the computer science division at UC Berkeley. She obtained her BS degree with a double major in mathematics and engineering and applied science from the California Institute of Technology in 2003. She obtained her Ph.D. in computer science from Carnegie Mellon University in 2008 under the guidance of Prof. Guy Blelloch. During the 2008-2009 academic year she was a member of the Institute for Advanced Study in Princeton, and for the following two years (2009-2011) she was a postdoctoral scholar at UC Berkeley mentored by Prof. Satish Rao and supported by a Computing Innovation Fellowship.