Re: [Rd] Suggest adding a 'pivot' argument to qr.R

From: Warnes, Gregory <gregory.warnes_at_novartis.com>
Date: Tue, 11 Sep 2012 14:02:15 +0000

On 9/7/12 2:42 PM, "peter dalgaard" <pdalgd_at_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.

-Greg

-- 
Gregory Warnes, Ph.D.
Sr. Expert Modeler
Modeling and Simulation
CA Phone: +1 617 871-8498
gregory.warnes_at_novartis.com

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