ESMF_DLAED6 Subroutine

subroutine ESMF_DLAED6(KNITER, ORGATI, RHO, D, Z, FINIT, TAU, INFO)

\brief \b ESMF_DLAED6 \htmlonly Download ESMF_DLAED6 + dependencies [TGZ] [ZIP] [TXT] \endhtmlonly \par Purpose:

\verbatim

ESMF_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 ESMF_DLAED4 when necessary. In most cases, the root sought is the smallest in magnitude, though it might not be in some extremely rare situations. \endverbatim \param[in] KNITER \verbatim KNITER is INTEGER Refer to ESMF_DLAED4 for its significance. \endverbatim

\param[in] ORGATI \verbatim 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 ESMF_DLAED4 for further details. \endverbatim

\param[in] RHO \verbatim RHO is DOUBLE PRECISION Refer to the equation f(x) above. \endverbatim

\param[in] D \verbatim D is DOUBLE PRECISION array, dimension (3) D satisfies d(1) < d(2) < d(3). \endverbatim

\param[in] Z \verbatim Z is DOUBLE PRECISION array, dimension (3) Each of the elements in z must be positive. \endverbatim

\param[in] FINIT \verbatim 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). \endverbatim

\param[out] TAU \verbatim TAU is DOUBLE PRECISION The root of the equation f(x). \endverbatim

\param[out] INFO \verbatim INFO is INTEGER = 0: successful exit > 0: if INFO = 1, failure to converge \endverbatim \author Univ. of Tennessee \author Univ. of California Berkeley \author Univ. of Colorado Denver \author NAG Ltd. \date November 2011 \ingroup auxOTHERcomputational \par Further Details:

\verbatim

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. \endverbatim \par Contributors:

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

Arguments