subroutine zlaqr1 (N, H, LDH, S1, S2, V)
subroutine zlaqr1 (integerN, complex*16, dimension( ldh, * )H, integerLDH, complex*16S1, complex*16S2, complex*16, dimension( * )V)ZLAQR1 sets a scalar multiple of the first column of the product of 2-by-2 or 3-by-3 matrix H and specified shifts. Purpose:
Given a 2-by-2 or 3-by-3 matrix H, ZLAQR1 sets v to a scalar multiple of the first column of the product (*) K = (H - s1*I)*(H - s2*I) scaling to avoid overflows and most underflows. This is useful for starting double implicit shift bulges in the QR algorithm.
N is integer Order of the matrix H. N must be either 2 or 3.H
H is COMPLEX*16 array of dimension (LDH,N) The 2-by-2 or 3-by-3 matrix H in (*).LDH
LDH is integer The leading dimension of H as declared in the calling procedure. LDH.GE.NS1
S1 is COMPLEX*16S2
S2 is COMPLEX*16 S1 and S2 are the shifts defining K in (*) above.V
V is COMPLEX*16 array of dimension N A scalar multiple of the first column of the matrix K in (*).
Univ. of Tennessee Univ. of California Berkeley Univ. of Colorado Denver NAG Ltd.Date:
Karen Braman and Ralph Byers, Department of Mathematics, University of Kansas, USADefinition at line 108 of file zlaqr1.f.