slaed6()

subroutine slaed6	(	integer	kniter,
		logical	orgati,
		real	rho,
		real, dimension( 3 )	d,
		real, dimension( 3 )	z,
		real	finit,
		real	tau,
		integer	info )

SLAED6 used by SSTEDC. Computes one Newton step in solution of the secular equation.

Download SLAED6 + dependencies [TGZ] [ZIP] [TXT]

Purpose:

!>
!> SLAED6 computes the positive or negative root (closest to the origin)
!> of
!>                  z(1)        z(2)        z(3)
!> f(x) =   rho + --------- + ---------- + ---------
!>                 d(1)-x      d(2)-x      d(3)-x
!>
!> It is assumed that
!>
!>       if ORGATI = .true. the root is between d(2) and d(3);
!>       otherwise it is between d(1) and d(2)
!>
!> This routine will be called by SLAED4 when necessary. In most cases,
!> the root sought is the smallest in magnitude, though it might not be
!> in some extremely rare situations.
!> 

Parameters

[in]	KNITER	!> KNITER is INTEGER !> Refer to SLAED4 for its significance. !>
[in]	ORGATI	!> ORGATI is LOGICAL !> If ORGATI is true, the needed root is between d(2) and !> d(3); otherwise it is between d(1) and d(2). See !> SLAED4 for further details. !>
[in]	RHO	!> RHO is REAL !> Refer to the equation f(x) above. !>
[in]	D	!> D is REAL array, dimension (3) !> D satisfies d(1) < d(2) < d(3). !>
[in]	Z	!> Z is REAL array, dimension (3) !> Each of the elements in z must be positive. !>
[in]	FINIT	!> FINIT is REAL !> The value of f at 0. It is more accurate than the one !> evaluated inside this routine (if someone wants to do !> so). !>
[out]	TAU	!> TAU is REAL !> The root of the equation f(x). !>
[out]	INFO	!> INFO is INTEGER !> = 0: successful exit !> > 0: if INFO = 1, failure to converge !>

Author

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Further Details:

!>
!>  10/02/03: This version has a few statements commented out for thread
!>  safety (machine parameters are computed on each entry). SJH.
!>
!>  05/10/06: Modified from a new version of Ren-Cang Li, use
!>     Gragg-Thornton-Warner cubic convergent scheme for better stability.
!> 

Contributors:

Ren-Cang Li, Computer Science Division, University of California at Berkeley, USA