dlaqr1.f man page

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 2-by-2 or 3-by-3 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 2-by-2 or 3-by-3 matrix H and specified shifts.

Purpose:

Given a 2-by-2 or 3-by-3 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 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

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.

Referenced By

dlaqr1(3) is an alias of dlaqr1.f(3).

Sat Nov 16 2013 Version 3.4.2 LAPACK