shseqr(3) on Linux
The text b37c1f0728b9, as Debian 1.3 (Bo) shipped it.
compute the eigenvalues of a real upper Hessenberg matrix H and, optionally, the matrices T and Z from the Schur decomposition H = Z T Z**T, where T is an upper quasi-triangular matrix (the Schur form), and Z is the orthogonal matrix of Schur vectors