dlaed6-f(3)

dlaed6.f –

Synopsis

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 (integerKNITER, logicalORGATI, double precisionRHO, double precision, dimension( 3 )D, double precision, dimension( 3 )Z, double precisionFINIT, double precisionTAU, integerINFO)

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

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:

KNITER

 KNITER is INTEGER
 Refer to DLAED4 for its significance.

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.

RHO

 RHO is DOUBLE PRECISION
 Refer to the equation f(x) above.

 D is DOUBLE PRECISION array, dimension (3)
 D satisfies d(1) < d(2) < d(3).

 Z is DOUBLE PRECISION array, dimension (3)
 Each of the elements in z must be positive.

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).

TAU

 TAU is DOUBLE PRECISION
 The root of the equation f(x).

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.

Author

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