LAPACK 3.11.0
LAPACK: Linear Algebra PACKage
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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