zlaqr1.f man page

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 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

Generated automatically by Doxygen for LAPACK from the source code.

Referenced By

zlaqr1(3) is an alias of zlaqr1.f(3).

Sat Nov 16 2013 Version 3.4.2 LAPACK