dhseqr(3) on Linux
The text 821a556bbb0a, as Debian 4.0 (Etch) 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