R help - Aug 2003 - Any symmetric matrix can be decomposed with eigendecomposition?

Hey, all

I have a question about the eigen-decomposition of a dxd symmatric matrix A.
Under what condition, that A can be decomposed such that A=U*D*U', where the
orthnormal matrix U is consisit of d eigenvectors and D is a diagonal matrix
with
eigenvalues in the diagonal positions.

Thanks for your help.

Fred