From pdalgd at gmail.com  Fri Sep  7 20:42:31 2012
From: pdalgd at gmail.com (peter dalgaard)
Date: Fri, 7 Sep 2012 20:42:31 +0200
Subject: [Rd] Suggest adding a 'pivot' argument to qr.R
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References: <CAAWNEwaZoBbM+V2eiLtWADX+7SEBZ1seX3iE0AeHGkdZMK4sJQ@mail.gmail.com>
Message-ID: <92D135CB-9634-4BAD-A8B8-F21A0A38B5C3@gmail.com>


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. 

-- 
Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com



[Rd] Suggest adding a 'pivot' argument to qr.R
peter dalgaard