claqr1.f

Section: LAPACK (3)
Updated: Tue Nov 14 2017
Page Index

NAME

claqr1.f

SYNOPSIS

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.

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

          H is COMPLEX 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 is COMPLEX

          S2 is COMPLEX

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

          V is COMPLEX 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 claqr1.f.

Author

Generated automatically by Doxygen for LAPACK from the source code.