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## dlarrr()

subroutine dlarrr | ( | integer | n,
|  | double precision, dimension( * ) | d,
|  | double precision, dimension( * ) | e,
|  | integer | info )

DLARRR performs tests to decide whether the symmetric tridiagonal matrix T warrants expensive computations which guarantee high relative accuracy in the eigenvalues.

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

Purpose:

      !>
      !> Perform tests to decide whether the symmetric tridiagonal matrix T
      !> warrants expensive computations which guarantee high relative accuracy
      !> in the eigenvalues.
      !>

Parameters

  [in]

  N

      !>          N is INTEGER
      !>          The order of the matrix. N > 0.
      !>

  [in]

  D

      !>          D is DOUBLE PRECISION array, dimension (N)
      !>          The N diagonal elements of the tridiagonal matrix T.
      !>

  [in,out]

  E

      !>          E is DOUBLE PRECISION array, dimension (N)
      !>          On entry, the first (N-1) entries contain the subdiagonal
      !>          elements of the tridiagonal matrix T; E(N) is set to ZERO.
      !>

  [out]

  INFO

      !>          INFO is INTEGER
      !>          INFO = 0(default) : the matrix warrants computations preserving
      !>                              relative accuracy.
      !>          INFO = 1          : the matrix warrants computations guaranteeing
      !>                              only absolute accuracy.
      !>

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

Contributors:
  Beresford Parlett, University of California, Berkeley, USA
  Jim Demmel, University of California, Berkeley, USA
  Inderjit Dhillon, University of Texas, Austin, USA
  Osni Marques, LBNL/NERSC, USA
  Christof Voemel, University of California, Berkeley, USA