zlaqr1.f man page

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 (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 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, 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, 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:

June 2017

Contributors:

Karen Braman and Ralph Byers, Department of Mathematics, University of Kansas, USA

Definition at line 109 of file zlaqr1.f.

Author

Generated automatically by Doxygen for LAPACK from the source code.

Referenced By

The man page zlaqr1(3) is an alias of zlaqr1.f(3).

Tue Nov 14 2017 Version 3.8.0 LAPACK