 LAPACK  3.4.2 LAPACK: Linear Algebra PACKage
zlaqr1.f File Reference

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## 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:
 [in] N ``` N is integer Order of the matrix H. N must be either 2 or 3.``` [in] H ``` H is COMPLEX*16 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*16` [in] S2 ``` S2 is COMPLEX*16 S1 and S2 are the shifts defining K in (*) above.``` [out] V ``` V is COMPLEX*16 array of dimension N A scalar multiple of the first column of the matrix K in (*).```
Date:
September 2012
Contributors:
Karen Braman and Ralph Byers, Department of Mathematics, University of Kansas, USA

Definition at line 108 of file zlaqr1.f.

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