LAPACK  3.7.0
LAPACK: Linear Algebra PACKage
subroutine dlasq4 ( integer  I0,
integer  N0,
double precision, dimension( * )  Z,
integer  PP,
integer  N0IN,
double precision  DMIN,
double precision  DMIN1,
double precision  DMIN2,
double precision  DN,
double precision  DN1,
double precision  DN2,
double precision  TAU,
integer  TTYPE,
double precision  G 
)

DLASQ4 computes an approximation to the smallest eigenvalue using values of d from the previous transform. Used by sbdsqr.

Download DLASQ4 + dependencies [TGZ] [ZIP] [TXT]

Purpose:
 DLASQ4 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 DOUBLE PRECISION 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 DOUBLE PRECISION
        Minimum value of d.
[in]DMIN1
          DMIN1 is DOUBLE PRECISION
        Minimum value of d, excluding D( N0 ).
[in]DMIN2
          DMIN2 is DOUBLE PRECISION
        Minimum value of d, excluding D( N0 ) and D( N0-1 ).
[in]DN
          DN is DOUBLE PRECISION
        d(N)
[in]DN1
          DN1 is DOUBLE PRECISION
        d(N-1)
[in]DN2
          DN2 is DOUBLE PRECISION
        d(N-2)
[out]TAU
          TAU is DOUBLE PRECISION
        This is the shift.
[out]TTYPE
          TTYPE is INTEGER
        Shift type.
[in,out]G
          G is DOUBLE PRECISION
        G is passed as an argument in order to save its value between
        calls to DLASQ4.
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date
June 2016
Further Details:
  CNST1 = 9/16