possible bug in det using method="qr" (PR#1244) - R-devel

Fri, Jan 4, 2002 4:48 PM #

Full_Name: Armin Roehrl
Version: 1.4.0(2001-12-19)
OS: Linux; Suse 7.3
Submission from: (NULL) (217.84.18.204)


Hello,

On a given matrix det returns different results whether
I use the method "qr" or "eivenvalues".

The matrix:

[,1]         [,2]        [,3]
[1,] 9.822616e+09 3.841723e+09    79790.09
[2,] 3.841723e+09 1.502536e+09    31251.82
[3,] 7.979009e+04 3.125182e+04 64156419.36

[1] -9.331893e+19

[1] 9.331893e+19

I think the result based on the eigenvalues is correct.

Good night.
	Armin

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Peter Dalgaard

Fri, Jan 4, 2002 6:10 PM #

armin@approximity.com writes:

That format is a bit awkward to key back in. Could you do a dput(m2)
so that it becomes easier for us to reproduce the effect?

O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard@biostat.ku.dk)             FAX: (+45) 35327907
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Armin Roehrl

Sat, Jan 5, 2002 1:50 AM #

Good morning,

structure(c(9822616000, 3841723000, 79790.09, 3841723000, 1502536000, 
31251.82, 79790.09, 31251.82, 64156419.36), .Dim = c(3, 3))

[1] -9.331893e+19

[1] 9.331893e+19

I hope it's not just some numerical accuracy thing and therefore
wasting your time.

Thx,
	Armin

On Saturday 05 January 2002 03:10, Peter Dalgaard BSA wrote:

Armin.

-----------------------------------------------
Armin Roehrl, http://www.approximity.com
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Peter Dalgaard

Sat, Jan 5, 2002 3:45 AM #

Armin Roehrl <armin@approximity.com> writes:

It's a numerical accuracy thing, but not a waste of time. The issue
is that qr() thinks that the matrix is singular:

[1] -9.331893e+19

[1] 9.331893e+19

Two issues here: 
(a) if qr() thinks a matrix is singular, I think det() should take the
consequences and return zero.
(b) Perhaps there ought to be a way to pass the tol= argument to det.

O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard@biostat.ku.dk)             FAX: (+45) 35327907
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