On Sep 11, 2012, at 16:02 , Warnes, Gregory wrote: > > On 9/7/12 2:42 PM, "peter dalgaard" <pda...@gmail.com> wrote: > >> >> On Sep 7, 2012, at 17:16 , Tim Hesterberg wrote: >> >>> I suggest adding a 'pivot' argument to qr.R, to obtain columns in the >>> same order as the original x, so that >>> a <- qr(x) >>> qr.Q(a) %*% qr.R(a, pivot=TRUE) >>> returns x. >> >> That would come spiraling down in flames the first time someone tried to >> use backsolve on it, wouldn't it? I mean, a major point of QR is that R >> is triangular; doesn't make much sense to permute the columns without >> retaining the pivoting permutation. > > As I understand Tim's proposal, the pivot argument defaults to FALSE, so > the new behavior would only be activated at the user's request.
Sure. I'm just saying that I see little use for the un-pivoted qr.R because, generically, the first thing you want to do with qr.R is to invert it, which is easier when it is triangular. -- Peter Dalgaard, Professor Center for Statistics, Copenhagen Business School Solbjerg Plads 3, 2000 Frederiksberg, Denmark Phone: (+45)38153501 Email: pd....@cbs.dk Priv: pda...@gmail.com ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
