LAPACK
3.4.2
LAPACK: Linear Algebra PACKage

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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. 
subroutine dlaqr5  (  logical  WANTT, 
logical  WANTZ,  
integer  KACC22,  
integer  N,  
integer  KTOP,  
integer  KBOT,  
integer  NSHFTS,  
double precision, dimension( * )  SR,  
double precision, dimension( * )  SI,  
double precision, dimension( ldh, * )  H,  
integer  LDH,  
integer  ILOZ,  
integer  IHIZ,  
double precision, dimension( ldz, * )  Z,  
integer  LDZ,  
double precision, dimension( ldv, * )  V,  
integer  LDV,  
double precision, dimension( ldu, * )  U,  
integer  LDU,  
integer  NV,  
double precision, dimension( ldwv, * )  WV,  
integer  LDWV,  
integer  NH,  
double precision, dimension( ldwh, * )  WH,  
integer  LDWH  
) 
DLAQR5 performs a single smallbulge multishift QR sweep.
Download DLAQR5 + dependencies [TGZ] [ZIP] [TXT]DLAQR5, called by DLAQR0, performs a single smallbulge multishift QR sweep.
[in]  WANTT  WANTT is logical scalar WANTT = .true. if the quasitriangular Schur factor is being computed. WANTT is set to .false. otherwise. 
[in]  WANTZ  WANTZ is logical scalar WANTZ = .true. if the orthogonal 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 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. 
[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,KTOP1) = 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]  SR  SR is DOUBLE PRECISION array of size (NSHFTS) 
[in,out]  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. 
[in,out]  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. 
[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 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. 
[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 DOUBLE PRECISION 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 DOUBLE PRECISION array of size (LDU,3*NSHFTS3) 
[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*NSHFTS3. 
[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 DOUBLE PRECISION 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*NSHFTS3. 
[in]  NV  NV is integer scalar NV is the number of rows in WV agailable for workspace. NV.GE.1. 
[out]  WV  WV is DOUBLE PRECISION array of size (LDWV,3*NSHFTS3) 
[in]  LDWV  LDWV is integer scalar LDWV is the leading dimension of WV as declared in the in the calling subroutine. LDWV.GE.NV. 
Definition at line 258 of file dlaqr5.f.