LAPACK Archives

[Lapack] eigenvector sign question

Dear Erich,

As I am sure you are aware, if x is an eigenvector corresponding to an 
eigenvalue lambda, then alpha*x, where alpha is a non-zero scalar, is 
also an eigenvector corresponding to lambda.  So, in particular we can 
choose alpha = +1 or -1.  The LAPACK symmetric eigenvalue routines 
return orthonormal eigenvectors, so that in particular norm(x) = 1, 
where norm is the 2-norm (Euclidean length), but do not choose any other 
scaling to further particularise x.

Best wishes,

Sven Hammarling.

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