zlaqr1.f(3) LAPACK zlaqr1.f(3)NAMEzlaqr1.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
2-by-2 or 3-by-3 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
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.
Parameters:
N
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.N
S1
S1 is COMPLEX*16
S2
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 (*).
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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Version 3.4.2 Tue Sep 25 2012 zlaqr1.f(3)