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.

N

          N is integer


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

H

          H is COMPLEX*16 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

          S1 is COMPLEX*16

S2

          S2 is COMPLEX*16


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

V

          V is COMPLEX*16 array of dimension N


              A scalar multiple of the first column of the


              matrix K in (*).

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

September 2012

Karen Braman and Ralph Byers, Department of Mathematics, University of Kansas, USA