[R] buggy eigen function

[Thomas Lumley]

On Tue, 21 Mar 2000, Chong Gu wrote:

> 
> It was a real surprise, but a student in my class found that the
> function eigen is buggy.  He traced to the problem from his inability
> of getting principal component analysis to work on his data.

I can't reproduce this problem.  I've tried on Linux and on AIX (which I
believe is your system) and I get

> jj
           [,1]      [,2]       [,3]
[1,]  0.8288469 -1.269783 -0.7533517
[2,] -1.2697830  2.162132  2.0262920
[3,] -0.7533517  2.026292  4.1927134
> eigen(jj)
$values
[1]  5.795187e+00  1.388505e+00 -2.006855e-07

$vectors
           [,1]       [,2]       [,3]
[1,] -0.3417893  0.4739218 -0.7067794
[2,]  0.7093264 -0.4978512 -0.5411749
[3,]  1.0576086  0.4870615  0.1345488


which looks right to me.

There may be a problem with your BLAS system or something. What OS and
compilers are you using?

	-thomas

Thomas Lumley
Assistant Professor, Biostatistics
University of Washington, Seattle


> 
> Chong Gu
> 
> 
> Here is a matrix I generated through X'X, where X is 2x3.
> 
> > jj
>            [,1]      [,2]       [,3]
> [1,]  0.8288469 -1.269783 -0.7533517
> [2,] -1.2697829  2.162132  2.0262917
> [3,] -0.7533517  2.026292  4.1927134
> 
> 
> Here are the 0.90.1 eigen results.
> 
> > eigen(jj)
> $values
> [1]  3.06206547  0.20492432 -0.04955518
> 
> $vectors
>            [,1]        [,2]        [,3]
> [1,] -0.2316032  0.05778620  0.06998513
> [2,]  0.4932735 -0.04951172  0.06919350
> [3,]  0.8489300  0.06527175 -0.01966568
> 
> 
> Here are the 1.0.0 eigen results.
> 
> > eigen(jj)
> $values
> [1]  2.765885782  0.008839573 -0.122630879
> 
> $vectors
>            [,1]       [,2]       [,3]
> [1,] -0.2236327  0.6670340  0.7106715
> [2,]  0.4693452 -0.5653355  0.6783147
> [3,]  0.8542268  0.4852437 -0.1866417
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Thomas Lumley
Assistant Professor, Biostatistics
University of Washington, Seattle

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