Communication Avoiding Rank Revealing QR Factorization with Column Pivoting
Résumé
In this paper we introduce CARRQR, a communication avoiding rank revealing QR
factorization with tournament pivoting. We show that CARRQR reveals the numerical rank of a
matrix in an analogous way to QR factorization with column pivoting (QRCP). Although the upper
bound of a quantity involved in the characterization of a rank revealing factorization is worse for
CARRQR than for QRCP, our numerical experiments on a set of challenging matrices show that
this upper bound is very pessimistic, and CARRQR is an effective tool in revealing the rank in practical
problems. Our main motivation for introducing CARRQR is that it minimizes data transfer,
modulo polylogarithmic factors, on both sequential and parallel machines, while previous factorizations
as QRCP are communication suboptimal and require asymptotically more communication than
CARRQR. Hence CARRQR is expected to have a better performance on current and future computers,
where communication is a major bottleneck that highly impacts the performance of an algorithm.