
dlaqr5.f(3) LAPACK dlaqr5.f(3)
NAME
dlaqr5.f 
SYNOPSIS
Functions/Subroutines
subroutine dlaqr5 (WANTT, WANTZ, KACC22, N, KTOP, KBOT, NSHFTS, SR, SI, H, LDH, ILOZ,
IHIZ, Z, LDZ, V, LDV, U, LDU, NV, WV, LDWV, NH, WH, LDWH)
DLAQR5 performs a single smallbulge multishift QR sweep.
Function/Subroutine Documentation
subroutine dlaqr5 (logicalWANTT, logicalWANTZ, integerKACC22, integerN, integerKTOP,
integerKBOT, integerNSHFTS, double precision, dimension( * )SR, double precision,
dimension( * )SI, double precision, dimension( ldh, * )H, integerLDH, integerILOZ,
integerIHIZ, double precision, dimension( ldz, * )Z, integerLDZ, double precision,
dimension( ldv, * )V, integerLDV, double precision, dimension( ldu, * )U, integerLDU,
integerNV, double precision, dimension( ldwv, * )WV, integerLDWV, integerNH, double
precision, dimension( ldwh, * )WH, integerLDWH)
DLAQR5 performs a single smallbulge multishift QR sweep.
Purpose:
DLAQR5, called by DLAQR0, performs a
single smallbulge multishift QR sweep.
Parameters:
WANTT
WANTT is logical scalar
WANTT = .true. if the quasitriangular Schur factor
is being computed. WANTT is set to .false. otherwise.
WANTZ
WANTZ is logical scalar
WANTZ = .true. if the orthogonal Schur factor is being
computed. WANTZ is set to .false. otherwise.
KACC22
KACC22 is integer with value 0, 1, or 2.
Specifies the computation mode of farfromdiagonal
orthogonal updates.
= 0: DLAQR5 does not accumulate reflections and does not
use matrixmatrix multiply to update farfromdiagonal
matrix entries.
= 1: DLAQR5 accumulates reflections and uses matrixmatrix
multiply to update the farfromdiagonal matrix entries.
= 2: DLAQR5 accumulates reflections, uses matrixmatrix
multiply to update the farfromdiagonal matrix entries,
and takes advantage of 2by2 block structure during
matrix multiplies.
N
N is integer scalar
N is the order of the Hessenberg matrix H upon which this
subroutine operates.
KTOP
KTOP is integer scalar
KBOT
KBOT is integer scalar
These are the first and last rows and columns of an
isolated diagonal block upon which the QR sweep is to be
applied. It is assumed without a check that
either KTOP = 1 or H(KTOP,KTOP1) = 0
and
either KBOT = N or H(KBOT+1,KBOT) = 0.
NSHFTS
NSHFTS is integer scalar
NSHFTS gives the number of simultaneous shifts. NSHFTS
must be positive and even.
SR
SR is DOUBLE PRECISION array of size (NSHFTS)
SI
SI is DOUBLE PRECISION array of size (NSHFTS)
SR contains the real parts and SI contains the imaginary
parts of the NSHFTS shifts of origin that define the
multishift QR sweep. On output SR and SI may be
reordered.
H
H is DOUBLE PRECISION array of size (LDH,N)
On input H contains a Hessenberg matrix. On output a
multishift QR sweep with shifts SR(J)+i*SI(J) is applied
to the isolated diagonal block in rows and columns KTOP
through KBOT.
LDH
LDH is integer scalar
LDH is the leading dimension of H just as declared in the
calling procedure. LDH.GE.MAX(1,N).
ILOZ
ILOZ is INTEGER
IHIZ
IHIZ is INTEGER
Specify the rows of Z to which transformations must be
applied if WANTZ is .TRUE.. 1 .LE. ILOZ .LE. IHIZ .LE. N
Z
Z is DOUBLE PRECISION array of size (LDZ,IHI)
If WANTZ = .TRUE., then the QR Sweep orthogonal
similarity transformation is accumulated into
Z(ILOZ:IHIZ,ILO:IHI) from the right.
If WANTZ = .FALSE., then Z is unreferenced.
LDZ
LDZ is integer scalar
LDA is the leading dimension of Z just as declared in
the calling procedure. LDZ.GE.N.
V
V is DOUBLE PRECISION array of size (LDV,NSHFTS/2)
LDV
LDV is integer scalar
LDV is the leading dimension of V as declared in the
calling procedure. LDV.GE.3.
U
U is DOUBLE PRECISION array of size
(LDU,3*NSHFTS3)
LDU
LDU is integer scalar
LDU is the leading dimension of U just as declared in the
in the calling subroutine. LDU.GE.3*NSHFTS3.
NH
NH is integer scalar
NH is the number of columns in array WH available for
workspace. NH.GE.1.
WH
WH is DOUBLE PRECISION array of size (LDWH,NH)
LDWH
LDWH is integer scalar
Leading dimension of WH just as declared in the
calling procedure. LDWH.GE.3*NSHFTS3.
NV
NV is integer scalar
NV is the number of rows in WV agailable for workspace.
NV.GE.1.
WV
WV is DOUBLE PRECISION array of size
(LDWV,3*NSHFTS3)
LDWV
LDWV is integer scalar
LDWV is the leading dimension of WV as declared in the
in the calling subroutine. LDWV.GE.NV.
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
References:
K. Braman, R. Byers and R. Mathias, The MultiShift QR Algorithm Part I: Maintaining
Well Focused Shifts, and Level 3 Performance, SIAM Journal of Matrix Analysis, volume
23, pages 929947, 2002.
Definition at line 258 of file dlaqr5.f.
Author
Generated automatically by Doxygen for LAPACK from the source code.
Version 3.4.2 Tue Sep 25 2012 dlaqr5.f(3) 
