A 3D Parallel Algorithm for QR Decomposition

Grey Ballard, James Demmel, Laura Grigori, Mathias Jacquelin, Nicholas Knight

Abstract: Interprocessor communication often dominates the runtime of large matrix computations. We present a parallel algorithm for computing QR decompositions whose bandwidth cost (communication volume) can be decreased at the cost of increasing its latency cost (number of messages). By varying a parameter to navigate the bandwidth/latency tradeoff, we can tune this algorithm for machines with different communication costs.