claqr1 (3)

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.

subroutine claqr1 (integerN, complex, dimension( ldh, * )H, integerLDH, complexS1, complexS2, 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.

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:

N

          N is integer
              Order of the matrix H. N must be either 2 or 3.

H

          H is COMPLEX 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

S2

          S2 is COMPLEX

          S1 and S2 are the shifts defining K in (*) above.

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.

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