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claqr1.f(3) LAPACK claqr1.f(3)

NAME

claqr1.f

SYNOPSIS

Functions/Subroutines


subroutine claqr1 (N, H, LDH, S1, S2, V)
CLAQR1 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 claqr1 (integer N, complex, dimension( ldh, * ) H, integer LDH, complex S1, complex S2, complex, dimension( * ) V)

CLAQR1 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, CLAQR1 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 array, 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

S2


S2 is COMPLEX
S1 and S2 are the shifts defining K in (*) above.

V


V is COMPLEX array, 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:

June 2017

Contributors:

Karen Braman and Ralph Byers, Department of Mathematics, University of Kansas, USA

Definition at line 109 of file claqr1.f.

Author

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Tue Nov 14 2017 Version 3.8.0