R devel - May 2007 - Bug in qr.R ? (PR#9655)

Ladies and Gentlemen,

using

 > A <- structure(c(1, 0, 0, 3, 2, 1, 4, 5, -3, -2, 1, 0), .Dim = 
as.integer(c(3,4)))

I get

 > dim(A)
[1] 3 4

 >  qr.R(qr(A),complete=TRUE)
     [,1]      [,2]      [,3]       [,4]
[1,]   -1 -3.000000 -4.000000  2.0000000
[2,]    0 -2.236068 -3.130495 -0.8944272
[3,]    0  0.000000 -4.919350 -0.4472136
 >  qr.R(qr(A),complete=FALSE)
     [,1]      [,2]      [,3]       [,4]
[1,]   -1 -3.000000 -4.000000  2.0000000
[2,]    0 -2.236068 -3.130495 -0.8944272
[3,]    0  0.000000 -4.919350 -0.4472136

In ?qr.R I find

/qr.R returns R. The number of rows of R is nrow(X) or ncol(X), 
depending on whether complete is TRUE or FALSE./

As you can see, the number of rows stays the same...
 
Thank you.

D. Trenkler

--please do not edit the information below--

Version:
 platform = i386-pc-mingw32
 arch = i386
 os = mingw32
 system = i386, mingw32
 status  major = 2
 minor = 5.0
 year = 2007
 month = 04
 day = 23
 svn rev = 41293
 language = R
 version.string = R version 2.5.0 (2007-04-23)

Windows XP (build 2600) Service Pack 2.0

Locale:
LC_COLLATE=English_United States.1252;LC_CTYPE=English_United 
States.1252;LC_MONETARY=English_United 
States.1252;LC_NUMERIC=C;LC_TIME=English_United States.1252

Search Path:
 .GlobalEnv, package:stats, package:graphics, package:grDevices, 
package:utils, package:datasets, package:methods, Autoloads, package:base

-- 
Dietrich Trenkler c/o Universitaet Osnabrueck 
Rolandstr. 8; D-49069 Osnabrueck, Germany    
email: Dietrich.Trenkler at Uni-Osnabrueck.de

And the purported bug is what: you failed to say!  This looks most like a 
misreading on your part of the documentation.

The help page says:

complete: logical expression of length 1.  Indicates whether an
           arbitrary  orthogonal completion of the *Q* or *X* matrices
           is to be made, or whether the *R* matrix is to be completed
           by binding zero-value rows beneath the square upper triangle.

You only need to complete R for n < p, as in:
> A <- matrix(1:12, 4)
>
>  qr.R(qr(A),complete=TRUE)
           [,1]       [,2]          [,3]
[1,] -5.477226 -12.780193 -2.008316e+01
[2,]  0.000000  -3.265986 -6.531973e+00
[3,]  0.000000   0.000000  2.641083e-15
[4,]  0.000000   0.000000  0.000000e+00
>  qr.R(qr(A),complete=FALSE)
           [,1]       [,2]          [,3]
[1,] -5.477226 -12.780193 -2.008316e+01
[2,]  0.000000  -3.265986 -6.531973e+00
[3,]  0.000000   0.000000  2.641083e-15


On Fri, 4 May 2007, Dietrich.Trenkler at uni-osnabrueck.de wrote:
> Ladies and Gentlemen,
>
> using
>
> > A <- structure(c(1, 0, 0, 3, 2, 1, 4, 5, -3, -2, 1, 0), .Dim >
as.integer(c(3,4)))
>
> I get
>
> > dim(A)
> [1] 3 4
>
> >  qr.R(qr(A),complete=TRUE)
>     [,1]      [,2]      [,3]       [,4]
> [1,]   -1 -3.000000 -4.000000  2.0000000
> [2,]    0 -2.236068 -3.130495 -0.8944272
> [3,]    0  0.000000 -4.919350 -0.4472136
> >  qr.R(qr(A),complete=FALSE)
>     [,1]      [,2]      [,3]       [,4]
> [1,]   -1 -3.000000 -4.000000  2.0000000
> [2,]    0 -2.236068 -3.130495 -0.8944272
> [3,]    0  0.000000 -4.919350 -0.4472136
>
> In ?qr.R I find
>
> /qr.R returns R. The number of rows of R is nrow(X) or ncol(X),
> depending on whether complete is TRUE or FALSE./
>
> As you can see, the number of rows stays the same...
But it says it is one of the two values, and that which depends on 
'complete' (but not that different values of 'complete'
necessarily give
different answers, just that they might).  You may have read this as if it 
said 'respectively', but it does not.

[...]

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595