claqr1-f(3)

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

 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 is COMPLEX

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

 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.

Author

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