LAPACK  3.4.2
LAPACK: Linear Algebra PACKage
 All Files Functions Groups
claqr1.f File Reference

Go to the source code of this file.

Functions/Subroutines

subroutine claqr1 (N, H, LDH, S1, S2, V)
 CLAQR1 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 claqr1 ( integer  N,
complex, dimension( ldh, * )  H,
integer  LDH,
complex  S1,
complex  S2,
complex, dimension( * )  V 
)

CLAQR1 sets a scalar multiple of the first column of the product of 2-by-2 or 3-by-3 matrix H and specified shifts.

Download CLAQR1 + dependencies [TGZ] [ZIP] [TXT]
Purpose:
      Given a 2-by-2 or 3-by-3 matrix H, CLAQR1 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:
[in]N
          N is integer
              Order of the matrix H. N must be either 2 or 3.
[in]H
          H is COMPLEX array of dimension (LDH,N)
              The 2-by-2 or 3-by-3 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
[in]S2
          S2 is COMPLEX

          S1 and S2 are the shifts defining K in (*) above.
[out]V
          V is COMPLEX 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 claqr1.f.

Here is the caller graph for this function: