From: Ravi Varadhan <rvaradha_at_jhsph.edu>

Date: Thu 05 May 2005 - 08:03:18 EST

Ravi Varadhan, Ph.D.

Assistant Professor, The Center on Aging and Health Division of Geriatric Medicine and Gerontology Johns Hopkins University

Ph: (410) 502-2619

Fax: (410) 614-9625

Email: rvaradhan@jhmi.edu

> -----Original Message-----

*> From: r-help-bounces@stat.math.ethz.ch [mailto:r-help-
*

*> bounces@stat.math.ethz.ch] On Behalf Of Duncan Murdoch
*

*> Sent: Wednesday, May 04, 2005 3:32 PM
*

*> To: Gabor Grothendieck
*

*> Cc: mingan; r-help@stat.math.ethz.ch; Huntsinger,Reid
*

*> Subject: Re: [R] rank of a matrix
*

*>
*

*> Gabor Grothendieck wrote:
*

*> > In this case, try a lower tolerance (1e-7 is the default):
*

*> >
*

*> >
*

*> >>qr(hilbert(9), tol = 1e-8)$rank
*

*> >
*

*> > [1] 9
*

*>
*

*> But don't trust the results. For example, create a matrix with 4
*

*> identical copies of hilbert(9). This still has rank 9. It's hard to
*

*> find, though:
*

*>
*

*> > h9 <- hilbert(9)
*

*> > temp <- cbind(h9, h9)
*

*> > h9times4 <- rbind(temp, temp)
*

*> >
*

*> > qr(h9times4,tol=1e-7)$rank
*

*> [1] 7
*

*> > qr(h9times4, tol=1e-8)$rank
*

*> [1] 10
*

*> > qr(h9times4, tol=1e-9)$rank
*

*> [1] 11
*

*> > qr(h9times4, tol=1e-10)$rank
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*> [1] 12
*

*>
*

*>
*

*> There's a tolerance that gives the right answer (1.5e-8 works for me),
*

*> but how would I know that in a real problem where I didn't already know
*

*> the answer?
*

*>
*

*> Duncan Murdoch
*

*>
*

*> ______________________________________________
*

*> R-help@stat.math.ethz.ch mailing list
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*> https://stat.ethz.ch/mailman/listinfo/r-help
*

*> PLEASE do read the posting guide! http://www.R-project.org/posting-
*

*> guide.html
*

R-help@stat.math.ethz.ch mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Thu May 05 08:12:28 2005

Date: Thu 05 May 2005 - 08:03:18 EST

Ravi Varadhan, Ph.D.

Assistant Professor, The Center on Aging and Health Division of Geriatric Medicine and Gerontology Johns Hopkins University

Ph: (410) 502-2619

Fax: (410) 614-9625

Email: rvaradhan@jhmi.edu

> -----Original Message-----

R-help@stat.math.ethz.ch mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Thu May 05 08:12:28 2005

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