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## slasq4()

subroutine slasq4 | ( | integer | i0,
|  | integer | n0,
|  | real, dimension( * ) | z,
|  | integer | pp,
|  | integer | n0in,
|  | real | dmin,
|  | real | dmin1,
|  | real | dmin2,
|  | real | dn,
|  | real | dn1,
|  | real | dn2,
|  | real | tau,
|  | integer | ttype,
|  | real | g )

SLASQ4 computes an approximation to the smallest eigenvalue using values of d from the previous transform. Used by sbdsqr.

Download SLASQ4 + dependencies [TGZ] [ZIP] [TXT]

Purpose:

      !>
      !> SLASQ4 computes an approximation TAU to the smallest eigenvalue
      !> using values of d from the previous transform.
      !>

Parameters

  [in]

  I0

      !>          I0 is INTEGER
      !>        First index.
      !>

  [in]

  N0

      !>          N0 is INTEGER
      !>        Last index.
      !>

  [in]

  Z

      !>          Z is REAL array, dimension ( 4*N0 )
      !>        Z holds the qd array.
      !>

  [in]

  PP

      !>          PP is INTEGER
      !>        PP=0 for ping, PP=1 for pong.
      !>

  [in]

  N0IN

      !>          N0IN is INTEGER
      !>        The value of N0 at start of EIGTEST.
      !>

  [in]

  DMIN

      !>          DMIN is REAL
      !>        Minimum value of d.
      !>

  [in]

  DMIN1

      !>          DMIN1 is REAL
      !>        Minimum value of d, excluding D( N0 ).
      !>

  [in]

  DMIN2

      !>          DMIN2 is REAL
      !>        Minimum value of d, excluding D( N0 ) and D( N0-1 ).
      !>

  [in]

  DN

      !>          DN is REAL
      !>        d(N)
      !>

  [in]

  DN1

      !>          DN1 is REAL
      !>        d(N-1)
      !>

  [in]

  DN2

      !>          DN2 is REAL
      !>        d(N-2)
      !>

  [out]

  TAU

      !>          TAU is REAL
      !>        This is the shift.
      !>

  [out]

  TTYPE

      !>          TTYPE is INTEGER
      !>        Shift type.
      !>

  [in,out]

  G

      !>          G is REAL
      !>        G is passed as an argument in order to save its value between
      !>        calls to SLASQ4.
      !>

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

Further Details:

      !>
      !>  CNST1 = 9/16
      !>