NAME

       slaed5.f -

SYNOPSIS

   Functions/Subroutines
       subroutine slaed5 (I, D, Z, DELTA, RHO, DLAM)
           SLAED5 used by sstedc. Solves the 2-by-2 secular equation.

Function/Subroutine Documentation

   subroutine slaed5 (integer I, real, dimension( 2 ) D, real, dimension( 2 ) Z, real, dimension(
       2 ) DELTA, real RHO, real DLAM)
       SLAED5 used by sstedc. Solves the 2-by-2 secular equation.

       Purpose:

            This subroutine computes the I-th eigenvalue of a symmetric rank-one
            modification of a 2-by-2 diagonal matrix

                       diag( D )  +  RHO * Z * transpose(Z) .

            The diagonal elements in the array D are assumed to satisfy

                       D(i) < D(j)  for  i < j .

            We also assume RHO > 0 and that the Euclidean norm of the vector
            Z is one.

       Parameters:
           I

                     I is INTEGER
                    The index of the eigenvalue to be computed.  I = 1 or I = 2.

           D

                     D is REAL array, dimension (2)
                    The original eigenvalues.  We assume D(1) < D(2).

           Z

                     Z is REAL array, dimension (2)
                    The components of the updating vector.

           DELTA

                     DELTA is REAL array, dimension (2)
                    The vector DELTA contains the information necessary
                    to construct the eigenvectors.

           RHO

                     RHO is REAL
                    The scalar in the symmetric updating formula.

           DLAM

                     DLAM is REAL
                    The computed lambda_I, the I-th updated eigenvalue.

       Author:
           Univ. of Tennessee

           Univ. of California Berkeley

           Univ. of Colorado Denver

           NAG Ltd.

       Date:
           September 2012

       Contributors:
           Ren-Cang Li, Computer Science Division, University of California at Berkeley, USA

Author

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