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| zlaqr1.f(3) | LAPACK | zlaqr1.f(3) | 
NAME¶
zlaqr1.f -SYNOPSIS¶
Functions/Subroutines¶
subroutine zlaqr1 (N, H, LDH, S1, S2, V)
Function/Subroutine Documentation¶
subroutine zlaqr1 (integerN, complex*16, dimension( ldh, * )H, integerLDH, complex*16S1, complex*16S2, complex*16, dimension( * )V)¶
ZLAQR1 Purpose:      Given a 2-by-2 or 3-by-3 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.
N
 
H
 
LDH
 
S1
 
S2
 
V
 
Author:
          N is integer
              Order of the matrix H. N must be either 2 or 3.
          H is COMPLEX*16 array of dimension (LDH,N)
              The 2-by-2 or 3-by-3 matrix H in (*).
          LDH is integer
              The leading dimension of H as declared in
              the calling procedure.  LDH.GE.N
S1 is COMPLEX*16
          S2 is COMPLEX*16
          S1 and S2 are the shifts defining K in (*) above.
          V is COMPLEX*16 array of dimension N
              A scalar multiple of the first column of the
              matrix K in (*).
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date:
November 2011
Contributors: 
Karen Braman and Ralph Byers, Department of
  Mathematics, University of Kansas, USA
Author¶
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