From gregory.warnes at novartis.com  Tue Sep 11 16:02:15 2012
From: gregory.warnes at novartis.com (Warnes, Gregory)
Date: Tue, 11 Sep 2012 14:02:15 +0000
Subject: [Rd] Suggest adding a 'pivot' argument to qr.R
In-Reply-To: <92D135CB-9634-4BAD-A8B8-F21A0A38B5C3@gmail.com>
Message-ID: <0CAEE2B1235DF643B0F5E1EAE1487B53094747F7@023-CH1MPN1-043.023d.mgd.msft.net>


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



[Rd] Suggest adding a 'pivot' argument to qr.R
Warnes, Gregory