
dlaqr1.f(3) LAPACK dlaqr1.f(3)
NAME
dlaqr1.f 
SYNOPSIS
Functions/Subroutines
subroutine dlaqr1 (N, H, LDH, SR1, SI1, SR2, SI2, V)
DLAQR1 sets a scalar multiple of the first column of the product of 2by2 or 3by3
matrix H and specified shifts.
Function/Subroutine Documentation
subroutine dlaqr1 (integerN, double precision, dimension( ldh, * )H, integerLDH, double
precisionSR1, double precisionSI1, double precisionSR2, double precisionSI2, double
precision, dimension( * )V)
DLAQR1 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, DLAQR1 sets v to a
scalar multiple of the first column of the product
(*) K = (H  (sr1 + i*si1)*I)*(H  (sr2 + i*si2)*I)
scaling to avoid overflows and most underflows. It
is assumed that either
1) sr1 = sr2 and si1 = si2
or
2) si1 = si2 = 0.
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 DOUBLE PRECISION array of dimension (LDH,N)
The 2by2 or 3by3 matrix H in (*).
LDH
LDH is integer
The leading dimension of H as declared in
the calling procedure. LDH.GE.N
SR1
SR1 is DOUBLE PRECISION
SI1
SI1 is DOUBLE PRECISION
SR2
SR2 is DOUBLE PRECISION
SI2
SI2 is DOUBLE PRECISION
The shifts in (*).
V
V is DOUBLE PRECISION 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 122 of file dlaqr1.f.
Author
Generated automatically by Doxygen for LAPACK from the source code.
Version 3.4.2 Tue Sep 25 2012 dlaqr1.f(3) 
