dlaqr1.f man page

dlaqr1.f —

Synopsis

Functions/Subroutines

subroutine dlaqr1 (N, H, LDH, SR1, SI1, SR2, SI2, V)
DLAQR1 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 dlaqr1 (integer N, double precision, dimension( ldh, * ) H, integer LDH, double precision SR1, double precision SI1, double precision SR2, double precision SI2, double precision, dimension( * ) V)

DLAQR1 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, DLAQR1 sets v to a
      scalar multiple of the first column of the product

      (*)  K = (H - (sr1 + i*si1)*I)*(H - (sr2 + i*si2)*I)

      scaling to avoid overflows and most underflows. It
      is assumed that either

              1) sr1 = sr2 and si1 = -si2
          or
              2) si1 = si2 = 0.

      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 DOUBLE PRECISION 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

SR1

          SR1 is DOUBLE PRECISION

SI1

          SI1 is DOUBLE PRECISION

SR2

          SR2 is DOUBLE PRECISION

SI2

          SI2 is DOUBLE PRECISION
              The shifts in (*).

V

          V is DOUBLE PRECISION 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 123 of file dlaqr1.f.

Author

Generated automatically by Doxygen for LAPACK from the source code.

Referenced By

The man page dlaqr1(3) is an alias of dlaqr1.f(3).

Sat Jun 24 2017 Version 3.7.1 LAPACK