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## dlaed5()

subroutine dlaed5 | ( | integer | i,
|  | double precision, dimension( 2 ) | d,
|  | double precision, dimension( 2 ) | z,
|  | double precision, dimension( 2 ) | delta,
|  | double precision | rho,
|  | double precision | dlam )

DLAED5 used by DSTEDC. Solves the 2-by-2 secular equation.

Download DLAED5 + dependencies [TGZ] [ZIP] [TXT]

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

  [in]

  I

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

  [in]

  D

      !>          D is DOUBLE PRECISION array, dimension (2)
      !>         The original eigenvalues.  We assume D(1) < D(2).
      !>

  [in]

  Z

      !>          Z is DOUBLE PRECISION array, dimension (2)
      !>         The components of the updating vector.
      !>

  [out]

  DELTA

      !>          DELTA is DOUBLE PRECISION array, dimension (2)
      !>         The vector DELTA contains the information necessary
      !>         to construct the eigenvectors.
      !>

  [in]

  RHO

      !>          RHO is DOUBLE PRECISION
      !>         The scalar in the symmetric updating formula.
      !>

  [out]

  DLAM

      !>          DLAM is DOUBLE PRECISION
      !>         The computed lambda_I, the I-th updated eigenvalue.
      !>

Author
  Univ. of Tennessee
  Univ. of California Berkeley
  Univ. of Colorado Denver
  NAG Ltd.

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