claqr1.f File Reference

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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.

Download CLAQR1 + dependencies [TGZ] [ZIP] [TXT]

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:

[in]	N	N is integer Order of the matrix H. N must be either 2 or 3.
[in]	H	H is COMPLEX array of dimension (LDH,N) The 2-by-2 or 3-by-3 matrix H in (*).
[in]	LDH	LDH is integer The leading dimension of H as declared in the calling procedure. LDH.GE.N
[in]	S1	S1 is COMPLEX
[in]	S2	S2 is COMPLEX S1 and S2 are the shifts defining K in (*) above.
[out]	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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