dlaed6(3)

NAME

DLAED6 - compute 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

SYNOPSIS

SUBROUTINE  DLAED6( KNITER, ORGATI, RHO, D, Z, FINIT, TAU,
INFO )
    LOGICAL        ORGATI
    INTEGER        INFO, KNITER
    DOUBLE         PRECISION FINIT, RHO, TAU
    DOUBLE         PRECISION D( 3 ), Z( 3 )

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.

ARGUMENTS

KNITER (input) INTEGER

Refer to DLAED4 for its significance.

ORGATI (input) 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 (input) DOUBLE PRECISION

Refer to the equation f(x) above.

D (input) DOUBLE PRECISION array, dimension (3)

D satisfies d(1) < d(2) < d(3).

Z (input) DOUBLE PRECISION array, dimension (3)

Each of the elements in z must be positive.

FINIT (input) 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 (output) DOUBLE PRECISION

The root of the equation f(x).

INFO (output) INTEGER

= 0: successful exit
> 0: if INFO = 1, failure to converge

FURTHER DETAILS

Based on contributions by

Ren-Cang Li, Computer Science Division, University of

California
at Berkeley, USA

LAPACK version 3.0 15 June 2000

DLAED6(3)