Approximate Gaussian Elimination for Laplacians: Fast, Sparse, and Simple

Presented on November 28, 2016 at 11:00 a.m. in the Klaus Advanced Computing Building, Room 1116E.Rasmus Kyng is a PhD student in Computer Science at Yale University, advised by Dan Spielman. Before attending Yale, he received a BA in Computer Science from the University of Cambridge in 2011. His research interests include graph algorithms, applied and theoretical machine learning, and linear systems.Runtime: 60:59 minutesWe show how to perform sparse approximate Gaussian elimination for Laplacian matrices. We present a simple, nearly linear time algorithm that approximates a Laplacian by a matrix with a sparse Cholesky factorization – the version of Gaussian elimination for positive semi-definite matrices. We compute this factorization by subsampling standard Gaussian elimination. This is the first nearly linear time solver for Laplacian systems that is based purely on random sampling, and does not use any graph theoretic constructions such as low-stretch trees, sparsifiers, or expanders. The crux of our proof is the use of matrix martingales to analyze the algorithm