 LAPACK  3.4.2 LAPACK: Linear Algebra PACKage
claqr5.f File Reference

Go to the source code of this file.

## Functions/Subroutines

subroutine claqr5 (WANTT, WANTZ, KACC22, N, KTOP, KBOT, NSHFTS, S, H, LDH, ILOZ, IHIZ, Z, LDZ, V, LDV, U, LDU, NV, WV, LDWV, NH, WH, LDWH)
CLAQR5 performs a single small-bulge multi-shift QR sweep.

## Function/Subroutine Documentation

 subroutine claqr5 ( logical WANTT, logical WANTZ, integer KACC22, integer N, integer KTOP, integer KBOT, integer NSHFTS, complex, dimension( * ) S, complex, dimension( ldh, * ) H, integer LDH, integer ILOZ, integer IHIZ, complex, dimension( ldz, * ) Z, integer LDZ, complex, dimension( ldv, * ) V, integer LDV, complex, dimension( ldu, * ) U, integer LDU, integer NV, complex, dimension( ldwv, * ) WV, integer LDWV, integer NH, complex, dimension( ldwh, * ) WH, integer LDWH )

CLAQR5 performs a single small-bulge multi-shift QR sweep.

Download CLAQR5 + dependencies [TGZ] [ZIP] [TXT]
Purpose:
```    CLAQR5 called by CLAQR0 performs a
single small-bulge multi-shift QR sweep.```
Parameters:
 [in] WANTT ``` WANTT is logical scalar WANTT = .true. if the triangular Schur factor is being computed. WANTT is set to .false. otherwise.``` [in] WANTZ ``` WANTZ is logical scalar WANTZ = .true. if the unitary Schur factor is being computed. WANTZ is set to .false. otherwise.``` [in] KACC22 ``` KACC22 is integer with value 0, 1, or 2. Specifies the computation mode of far-from-diagonal orthogonal updates. = 0: CLAQR5 does not accumulate reflections and does not use matrix-matrix multiply to update far-from-diagonal matrix entries. = 1: CLAQR5 accumulates reflections and uses matrix-matrix multiply to update the far-from-diagonal matrix entries. = 2: CLAQR5 accumulates reflections, uses matrix-matrix multiply to update the far-from-diagonal matrix entries, and takes advantage of 2-by-2 block structure during matrix multiplies.``` [in] N ``` N is integer scalar N is the order of the Hessenberg matrix H upon which this subroutine operates.``` [in] KTOP ` KTOP is integer scalar` [in] 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,KTOP-1) = 0 and either KBOT = N or H(KBOT+1,KBOT) = 0.``` [in] NSHFTS ``` NSHFTS is integer scalar NSHFTS gives the number of simultaneous shifts. NSHFTS must be positive and even.``` [in,out] S ``` S is COMPLEX array of size (NSHFTS) S contains the shifts of origin that define the multi- shift QR sweep. On output S may be reordered.``` [in,out] H ``` H is COMPLEX array of size (LDH,N) On input H contains a Hessenberg matrix. On output a multi-shift QR sweep with shifts SR(J)+i*SI(J) is applied to the isolated diagonal block in rows and columns KTOP through KBOT.``` [in] LDH ``` LDH is integer scalar LDH is the leading dimension of H just as declared in the calling procedure. LDH.GE.MAX(1,N).``` [in] ILOZ ` ILOZ is INTEGER` [in] 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``` [in,out] Z ``` Z is COMPLEX array of size (LDZ,IHI) If WANTZ = .TRUE., then the QR Sweep unitary similarity transformation is accumulated into Z(ILOZ:IHIZ,ILO:IHI) from the right. If WANTZ = .FALSE., then Z is unreferenced.``` [in] LDZ ``` LDZ is integer scalar LDA is the leading dimension of Z just as declared in the calling procedure. LDZ.GE.N.``` [out] V ` V is COMPLEX array of size (LDV,NSHFTS/2)` [in] LDV ``` LDV is integer scalar LDV is the leading dimension of V as declared in the calling procedure. LDV.GE.3.``` [out] U ``` U is COMPLEX array of size (LDU,3*NSHFTS-3)``` [in] LDU ``` LDU is integer scalar LDU is the leading dimension of U just as declared in the in the calling subroutine. LDU.GE.3*NSHFTS-3.``` [in] NH ``` NH is integer scalar NH is the number of columns in array WH available for workspace. NH.GE.1.``` [out] WH ` WH is COMPLEX array of size (LDWH,NH)` [in] LDWH ``` LDWH is integer scalar Leading dimension of WH just as declared in the calling procedure. LDWH.GE.3*NSHFTS-3.``` [in] NV ``` NV is integer scalar NV is the number of rows in WV agailable for workspace. NV.GE.1.``` [out] WV ``` WV is COMPLEX array of size (LDWV,3*NSHFTS-3)``` [in] LDWV ``` LDWV is integer scalar LDWV is the leading dimension of WV as declared in the in the calling subroutine. LDWV.GE.NV.```
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 Multi-Shift QR Algorithm Part I: Maintaining Well Focused Shifts, and Level 3 Performance, SIAM Journal of Matrix Analysis, volume 23, pages 929–947, 2002.

Definition at line 250 of file claqr5.f.

Here is the call graph for this function:

Here is the caller graph for this function: