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Communication Avoiding Algorithms for Linear Algebra and Beyond

Speaker: Professor James Demmel
University of California, Berkeley

November 7, 2012 - 4:00 p.m. to 5:00 p.m.
Reception at 3:3opm
Location: DCC 337
Hosted By: Prof. Fran Berman (x4873)


Algorithms have two costs: arithmetic and communication, i.e. moving data between levels of a memory hierarchy or processors over a network. Communication costs (measured in time or energy per operation) already greatly exceed arithmetic costs, and the gap is growing over time following technological trends. Thus our goal is to design algorithms that minimize communication. We present algorithms that attain provable lower bounds on communication, and show large speedups compared to their conventional counterparts. These algorithms are for direct and iterative linear algebra, for dense and sparse matrices, as well as direct n-body simulations. Several of these algorithms exhibit perfect strong scaling, in both time and energy: run time (resp. energy) for a fixed problem size drops proportionally to p (resp. is independent of p). Finally, we describe extensions to algorithms involving arbitrary loop nests and array accesses, assuming only that array subscripts are linear functions of the loop indices.


James Demmel is the Dr. Richard Carl Dehmel Distinguished Professor of Computer Science and Mathematics at the University of California at Berkeley. His personal research interests are in numerical linear algebra, high performance computing, and communication avoiding algorithms in general. He is known for his work on the LAPACK and ScaL APACK linear algebra libraries. He is a member of the National Academy of Sciences, National Academy of Engineering, a Fellow of the ACM, IEEE and SIAM, and winner of the IEEE Computer Society Sidney Fernbach Award, the SIAM J. H. Wilkinson Prize in Numerical Analysis and Scientific Computing, and numerous best paper prizes, including being the only 3-time winner of the SIAM Linear Algebra (SIAG/LA) Prize. He was an invited speaker at the 2002 International Congress of Mathematicians and the 2003 International Congress on Industrial and Applied Mathematics.

Last updated: October 23, 2012