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SRC/lapack_64_obj/dlaqr1.f(3) Library Functions Manual SRC/lapack_64_obj/dlaqr1.f(3)

NAME

SRC/lapack_64_obj/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 (integer n, double precision, dimension( ldh, * ) h, integer ldh, double precision sr1, double precision si1, double precision sr2, double precision si2, 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, 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 >= 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, 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.

Contributors:

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

Definition at line 121 of file dlaqr1.f.

Author

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Version 3.12.1 LAPACK