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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)
 
ZLAQR1 sets a scalar multiple of the first column of the product of 2-by-2 or 3-by-3 matrix H and specified shifts.

Function/Subroutine Documentation

subroutine zlaqr1 (integerN, complex*16, dimension( ldh, * )H, integerLDH, complex*16S1, complex*16S2, complex*16, dimension( * )V)

ZLAQR1 sets a scalar multiple of the first column of the product of 2-by-2 or 3-by-3 matrix H and specified shifts.
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.
Parameters:
N 
          N is integer
              Order of the matrix H. N must be either 2 or 3.
H 
          H is COMPLEX*16 array of dimension (LDH,N)
              The 2-by-2 or 3-by-3 matrix H in (*).
LDH 
          LDH is integer
              The leading dimension of H as declared in
              the calling procedure.  LDH.GE.N
S1 
          S1 is COMPLEX*16
S2 
          S2 is COMPLEX*16


          S1 and S2 are the shifts defining K in (*) above.
V 
          V is COMPLEX*16 array of dimension N
              A scalar multiple of the first column of the
              matrix K in (*).
Author:
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date:
September 2012
Contributors:
Karen Braman and Ralph Byers, Department of Mathematics, University of Kansas, USA
Definition at line 108 of file zlaqr1.f.

Author

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