CLAQR1(3)      LAPACK routine of NEC Numeric Library Collection      CLAQR1(3)



NAME
       CLAQR1

SYNOPSIS
       SUBROUTINE CLAQR1 (N, H, LDH, S1, S2, V)



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.




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

           H         (input)
                     H is COMPLEX array of dimension (LDH,N)
                         The 2-by-2 or 3-by-3 matrix H in (*).

           LDH       (input)
                     LDH is integer
                         The leading dimension of H as declared in
                         the calling procedure.  LDH.GE.N

           S1        (input)
                     S1 is COMPLEX

           S2        (input)
                     S2 is COMPLEX

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

           V         (output)
                     V is COMPLEX array of dimension N
                         A scalar multiple of the first column of the
                         matrix K in (*).



LAPACK routine                  31 October 2017                      CLAQR1(3)