LAPACK 3.11.0
LAPACK: Linear Algebra PACKage

◆ dlasq4()

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.
Further Details:
  CNST1 = 9/16