
slaqr2.f(3) LAPACK slaqr2.f(3)
NAME
slaqr2.f 
SYNOPSIS
Functions/Subroutines
subroutine slaqr2 (WANTT, WANTZ, N, KTOP, KBOT, NW, H, LDH, ILOZ, IHIZ, Z, LDZ, NS, ND,
SR, SI, V, LDV, NH, T, LDT, NV, WV, LDWV, WORK, LWORK)
SLAQR2 performs the orthogonal similarity transformation of a Hessenberg matrix to
detect and deflate fully converged eigenvalues from a trailing principal submatrix
(aggressive early deflation).
Function/Subroutine Documentation
subroutine slaqr2 (logicalWANTT, logicalWANTZ, integerN, integerKTOP, integerKBOT, integerNW,
real, dimension( ldh, * )H, integerLDH, integerILOZ, integerIHIZ, real, dimension( ldz, *
)Z, integerLDZ, integerNS, integerND, real, dimension( * )SR, real, dimension( * )SI,
real, dimension( ldv, * )V, integerLDV, integerNH, real, dimension( ldt, * )T, integerLDT,
integerNV, real, dimension( ldwv, * )WV, integerLDWV, real, dimension( * )WORK,
integerLWORK)
SLAQR2 performs the orthogonal similarity transformation of a Hessenberg matrix to detect
and deflate fully converged eigenvalues from a trailing principal submatrix (aggressive
early deflation).
Purpose:
SLAQR2 is identical to SLAQR3 except that it avoids
recursion by calling SLAHQR instead of SLAQR4.
Aggressive early deflation:
This subroutine accepts as input an upper Hessenberg matrix
H and performs an orthogonal similarity transformation
designed to detect and deflate fully converged eigenvalues from
a trailing principal submatrix. On output H has been over
written by a new Hessenberg matrix that is a perturbation of
an orthogonal similarity transformation of H. It is to be
hoped that the final version of H has many zero subdiagonal
entries.
Parameters:
WANTT
WANTT is LOGICAL
If .TRUE., then the Hessenberg matrix H is fully updated
so that the quasitriangular Schur factor may be
computed (in cooperation with the calling subroutine).
If .FALSE., then only enough of H is updated to preserve
the eigenvalues.
WANTZ
WANTZ is LOGICAL
If .TRUE., then the orthogonal matrix Z is updated so
so that the orthogonal Schur factor may be computed
(in cooperation with the calling subroutine).
If .FALSE., then Z is not referenced.
N
N is INTEGER
The order of the matrix H and (if WANTZ is .TRUE.) the
order of the orthogonal matrix Z.
KTOP
KTOP is INTEGER
It is assumed that either KTOP = 1 or H(KTOP,KTOP1)=0.
KBOT and KTOP together determine an isolated block
along the diagonal of the Hessenberg matrix.
KBOT
KBOT is INTEGER
It is assumed without a check that either
KBOT = N or H(KBOT+1,KBOT)=0. KBOT and KTOP together
determine an isolated block along the diagonal of the
Hessenberg matrix.
NW
NW is INTEGER
Deflation window size. 1 .LE. NW .LE. (KBOTKTOP+1).
H
H is REAL array, dimension (LDH,N)
On input the initial NbyN section of H stores the
Hessenberg matrix undergoing aggressive early deflation.
On output H has been transformed by an orthogonal
similarity transformation, perturbed, and the returned
to Hessenberg form that (it is to be hoped) has some
zero subdiagonal entries.
LDH
LDH is integer
Leading dimension of H just as declared in the calling
subroutine. N .LE. LDH
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 REAL array, dimension (LDZ,N)
IF WANTZ is .TRUE., then on output, the orthogonal
similarity transformation mentioned above has been
accumulated into Z(ILOZ:IHIZ,ILO:IHI) from the right.
If WANTZ is .FALSE., then Z is unreferenced.
LDZ
LDZ is integer
The leading dimension of Z just as declared in the
calling subroutine. 1 .LE. LDZ.
NS
NS is integer
The number of unconverged (ie approximate) eigenvalues
returned in SR and SI that may be used as shifts by the
calling subroutine.
ND
ND is integer
The number of converged eigenvalues uncovered by this
subroutine.
SR
SR is REAL array, dimension KBOT
SI
SI is REAL array, dimension KBOT
On output, the real and imaginary parts of approximate
eigenvalues that may be used for shifts are stored in
SR(KBOTNDNS+1) through SR(KBOTND) and
SI(KBOTNDNS+1) through SI(KBOTND), respectively.
The real and imaginary parts of converged eigenvalues
are stored in SR(KBOTND+1) through SR(KBOT) and
SI(KBOTND+1) through SI(KBOT), respectively.
V
V is REAL array, dimension (LDV,NW)
An NWbyNW work array.
LDV
LDV is integer scalar
The leading dimension of V just as declared in the
calling subroutine. NW .LE. LDV
NH
NH is integer scalar
The number of columns of T. NH.GE.NW.
T
T is REAL array, dimension (LDT,NW)
LDT
LDT is integer
The leading dimension of T just as declared in the
calling subroutine. NW .LE. LDT
NV
NV is integer
The number of rows of work array WV available for
workspace. NV.GE.NW.
WV
WV is REAL array, dimension (LDWV,NW)
LDWV
LDWV is integer
The leading dimension of W just as declared in the
calling subroutine. NW .LE. LDV
WORK
WORK is REAL array, dimension LWORK.
On exit, WORK(1) is set to an estimate of the optimal value
of LWORK for the given values of N, NW, KTOP and KBOT.
LWORK
LWORK is integer
The dimension of the work array WORK. LWORK = 2*NW
suffices, but greater efficiency may result from larger
values of LWORK.
If LWORK = 1, then a workspace query is assumed; SLAQR2
only estimates the optimal workspace size for the given
values of N, NW, KTOP and KBOT. The estimate is returned
in WORK(1). No error message related to LWORK is issued
by XERBLA. Neither H nor Z are accessed.
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 277 of file slaqr2.f.
Author
Generated automatically by Doxygen for LAPACK from the source code.
Version 3.4.2 Tue Sep 25 2012 slaqr2.f(3) 
