LAPACK
3.4.2
LAPACK: Linear Algebra PACKage

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Functions/Subroutines  
subroutine  zlaqr1 (N, H, LDH, S1, S2, V) 
ZLAQR1 sets a scalar multiple of the first column of the product of 2by2 or 3by3 matrix H and specified shifts. 
subroutine zlaqr1  (  integer  N, 
complex*16, dimension( ldh, * )  H,  
integer  LDH,  
complex*16  S1,  
complex*16  S2,  
complex*16, dimension( * )  V  
) 
ZLAQR1 sets a scalar multiple of the first column of the product of 2by2 or 3by3 matrix H and specified shifts.
Download ZLAQR1 + dependencies [TGZ] [ZIP] [TXT]Given a 2by2 or 3by3 matrix H, ZLAQR1 sets v to a scalar multiple of the first column of the product (*) K = (H  s1*I)*(H  s2*I) scaling to avoid overflows and most underflows. This is useful for starting double implicit shift bulges in the QR algorithm.
[in]  N  N is integer Order of the matrix H. N must be either 2 or 3. 
[in]  H  H is COMPLEX*16 array of dimension (LDH,N) The 2by2 or 3by3 matrix H in (*). 
[in]  LDH  LDH is integer The leading dimension of H as declared in the calling procedure. LDH.GE.N 
[in]  S1  S1 is COMPLEX*16 
[in]  S2  S2 is COMPLEX*16 S1 and S2 are the shifts defining K in (*) above. 
[out]  V  V is COMPLEX*16 array of dimension N A scalar multiple of the first column of the matrix K in (*). 
Definition at line 108 of file zlaqr1.f.