slaqr1 (3)  Linux Manuals
NAME
slaqr1.f 
SYNOPSIS
Functions/Subroutines
subroutine slaqr1 (N, H, LDH, SR1, SI1, SR2, SI2, V)
SLAQR1 sets a scalar multiple of the first column of the product of 2by2 or 3by3 matrix H and specified shifts.
Function/Subroutine Documentation
subroutine slaqr1 (integerN, real, dimension( ldh, * )H, integerLDH, realSR1, realSI1, realSR2, realSI2, real, dimension( * )V)
SLAQR1 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, SLAQR1 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.
HH is REAL 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
SR1SR1 is REAL
SI1SI1 is REAL
SR2SR2 is REAL
SI2SI2 is REAL The shifts in (*).
VV is REAL 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 slaqr1.f.
Author
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