NAME

       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

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

           H

                     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

                     S1 is COMPLEX

           S2

                     S2 is COMPLEX

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

           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.

Author

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