LAPACK
3.4.2
LAPACK: Linear Algebra PACKage

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Functions/Subroutines  
subroutine  slaqr3 (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) 
SLAQR3 performs the orthogonal similarity transformation of a Hessenberg matrix to detect and deflate fully converged eigenvalues from a trailing principal submatrix (aggressive early deflation). 
subroutine slaqr3  (  logical  WANTT, 
logical  WANTZ,  
integer  N,  
integer  KTOP,  
integer  KBOT,  
integer  NW,  
real, dimension( ldh, * )  H,  
integer  LDH,  
integer  ILOZ,  
integer  IHIZ,  
real, dimension( ldz, * )  Z,  
integer  LDZ,  
integer  NS,  
integer  ND,  
real, dimension( * )  SR,  
real, dimension( * )  SI,  
real, dimension( ldv, * )  V,  
integer  LDV,  
integer  NH,  
real, dimension( ldt, * )  T,  
integer  LDT,  
integer  NV,  
real, dimension( ldwv, * )  WV,  
integer  LDWV,  
real, dimension( * )  WORK,  
integer  LWORK  
) 
SLAQR3 performs the orthogonal similarity transformation of a Hessenberg matrix to detect and deflate fully converged eigenvalues from a trailing principal submatrix (aggressive early deflation).
Download SLAQR3 + dependencies [TGZ] [ZIP] [TXT]Aggressive early deflation: SLAQR3 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.
[in]  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. 
[in]  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. 
[in]  N  N is INTEGER The order of the matrix H and (if WANTZ is .TRUE.) the order of the orthogonal matrix Z. 
[in]  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. 
[in]  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. 
[in]  NW  NW is INTEGER Deflation window size. 1 .LE. NW .LE. (KBOTKTOP+1). 
[in,out]  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. 
[in]  LDH  LDH is integer Leading dimension of H just as declared in the calling subroutine. N .LE. LDH 
[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 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. 
[in]  LDZ  LDZ is integer The leading dimension of Z just as declared in the calling subroutine. 1 .LE. LDZ. 
[out]  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. 
[out]  ND  ND is integer The number of converged eigenvalues uncovered by this subroutine. 
[out]  SR  SR is REAL array, dimension KBOT 
[out]  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. 
[out]  V  V is REAL array, dimension (LDV,NW) An NWbyNW work array. 
[in]  LDV  LDV is integer scalar The leading dimension of V just as declared in the calling subroutine. NW .LE. LDV 
[in]  NH  NH is integer scalar The number of columns of T. NH.GE.NW. 
[out]  T  T is REAL array, dimension (LDT,NW) 
[in]  LDT  LDT is integer The leading dimension of T just as declared in the calling subroutine. NW .LE. LDT 
[in]  NV  NV is integer The number of rows of work array WV available for workspace. NV.GE.NW. 
[out]  WV  WV is REAL array, dimension (LDWV,NW) 
[in]  LDWV  LDWV is integer The leading dimension of W just as declared in the calling subroutine. NW .LE. LDV 
[out]  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. 
[in]  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; SLAQR3 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. 
Definition at line 274 of file slaqr3.f.