dlaed6.f File Reference

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Functions/Subroutines
subroutine	dlaed6 (KNITER, ORGATI, RHO, D, Z, FINIT, TAU, INFO)
	DLAED6 used by sstedc. Computes one Newton step in solution of the secular equation.

---

Function/Subroutine Documentation

subroutine dlaed6	(	integer	KNITER,
		logical	ORGATI,
		double precision	RHO,
		double precision, dimension( 3 )	D,
		double precision, dimension( 3 )	Z,
		double precision	FINIT,
		double precision	TAU,
		integer	INFO
	)

DLAED6 used by sstedc. Computes one Newton step in solution of the secular equation.

Download DLAED6 + dependencies [TGZ] [ZIP] [TXT]

Purpose:

 DLAED6 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 DLAED4 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 DLAED4 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 DLAED4 for further details.
[in]	RHO	RHO is DOUBLE PRECISION Refer to the equation f(x) above.
[in]	D	D is DOUBLE PRECISION array, dimension (3) D satisfies d(1) < d(2) < d(3).
[in]	Z	Z is DOUBLE PRECISION array, dimension (3) Each of the elements in z must be positive.
[in]	FINIT	FINIT is DOUBLE PRECISION 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 DOUBLE PRECISION 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.

Date:

September 2012

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

Definition at line 141 of file dlaed6.f.

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