zlaqr1.f (3)  Linux Manuals
NAME
zlaqr1.f 
SYNOPSIS
Functions/Subroutines
subroutine zlaqr1 (N, H, LDH, S1, S2, V)
ZLAQR1 sets a scalar multiple of the first column of the product of 2by2 or 3by3 matrix H and specified shifts.
Function/Subroutine Documentation
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 2by2 or 3by3 matrix H and specified shifts.
Purpose:

Given a 2by2 or 3by3 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.
Parameters:

N
N is integer Order of the matrix H. N must be either 2 or 3.
HH is COMPLEX*16 array of dimension (LDH,N) The 2by2 or 3by3 matrix H in (*).
LDHLDH is integer The leading dimension of H as declared in the calling procedure. LDH.GE.N
S1S1 is COMPLEX*16
S2S2 is COMPLEX*16 S1 and S2 are the shifts defining K in (*) above.
VV is COMPLEX*16 array of dimension N A scalar multiple of the first column of the matrix K in (*).
Author:

Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date:
 September 2012
Contributors:
 Karen Braman and Ralph Byers, Department of Mathematics, University of Kansas, USA
Definition at line 108 of file zlaqr1.f.
Author
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