LAPACK  3.9.0
LAPACK: Linear Algebra PACKage

◆ 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.
Date
June 2016
Further Details:
  CNST1 = 9/16