# [Rd] Re: [R] non-ideal behavior in princomp/ not a feature but a bug

**Paul Gilbert
**
pgilbert@bank-banque-canada.ca

*Fri, 29 Sep 2000 09:37:47 -0400*

>*2. However, not all matrices work, such as the first one I tried yesterday.
*>*Here is
*>*an example of a matrix which does not work.
*>>* x
*>* [,1] [,2] [,3] [,4]
*>*[1,] -0.4 -1.6 -1.0 -1.8
*>*[2,] -2.2 -0.3 1.4 0.2
*>>* princomp(x)
*>*Error in princomp(x) : covariance matrix is not non-negative definite
*
This does not happen with this example in Solaris, but I have had similar
problems with eigen before and had to use something like eigen( (cv + t(cv))/2 )
to avoid it. It seems to me that if eigen is called with symmetric = TRUE, as is
done in princomp, then eigen should return an error message about a
non-symmetric matrix, rather than return a possibly spurious answer from which
negative eigenvalues are checked to test for a non symmetric matrix.
Paul Gilbert
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