dlaed6(3F)

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
           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