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Abdelrahman Said
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/* -- translated by f2c (version 20240504).
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You must link the resulting object file with libf2c:
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on Microsoft Windows system, link with libf2c.lib;
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on Linux or Unix systems, link with .../path/to/libf2c.a -lm
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or, if you install libf2c.a in a standard place, with -lf2c -lm
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-- in that order, at the end of the command line, as in
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cc *.o -lf2c -lm
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Source for libf2c is in /netlib/f2c/libf2c.zip, e.g.,
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http://www.netlib.org/f2c/libf2c.zip
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*/
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#include "f2c.h"
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/* > \brief \b DLASQ6 computes one dqd transform in ping-pong form. Used by sbdsqr and sstegr.
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=========== DOCUMENTATION ===========
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Online html documentation available at
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http://www.netlib.org/lapack/explore-html/
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> \htmlonly
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> Download DLASQ6 + dependencies
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> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/dlasq6.
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f">
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> [TGZ]</a>
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> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/dlasq6.
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f">
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> [ZIP]</a>
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> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/dlasq6.
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f">
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> [TXT]</a>
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> \endhtmlonly
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Definition:
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===========
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SUBROUTINE DLASQ6( I0, N0, Z, PP, DMIN, DMIN1, DMIN2, DN,
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DNM1, DNM2 )
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INTEGER I0, N0, PP
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DOUBLE PRECISION DMIN, DMIN1, DMIN2, DN, DNM1, DNM2
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DOUBLE PRECISION Z( * )
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> \par Purpose:
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=============
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>
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> \verbatim
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>
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> DLASQ6 computes one dqd (shift equal to zero) transform in
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> ping-pong form, with protection against underflow and overflow.
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> \endverbatim
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Arguments:
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==========
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> \param[in] I0
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> \verbatim
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> I0 is INTEGER
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> First index.
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> \endverbatim
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>
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> \param[in] N0
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> \verbatim
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> N0 is INTEGER
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> Last index.
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> \endverbatim
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>
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> \param[in] Z
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> \verbatim
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> Z is DOUBLE PRECISION array, dimension ( 4*N )
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> Z holds the qd array. EMIN is stored in Z(4*N0) to avoid
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> an extra argument.
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> \endverbatim
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>
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> \param[in] PP
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> \verbatim
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> PP is INTEGER
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> PP=0 for ping, PP=1 for pong.
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> \endverbatim
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>
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> \param[out] DMIN
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> \verbatim
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> DMIN is DOUBLE PRECISION
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> Minimum value of d.
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> \endverbatim
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>
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> \param[out] DMIN1
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> \verbatim
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> DMIN1 is DOUBLE PRECISION
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> Minimum value of d, excluding D( N0 ).
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> \endverbatim
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>
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> \param[out] DMIN2
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> \verbatim
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> DMIN2 is DOUBLE PRECISION
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> Minimum value of d, excluding D( N0 ) and D( N0-1 ).
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> \endverbatim
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>
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> \param[out] DN
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> \verbatim
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> DN is DOUBLE PRECISION
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> d(N0), the last value of d.
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> \endverbatim
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>
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> \param[out] DNM1
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> \verbatim
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> DNM1 is DOUBLE PRECISION
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> d(N0-1).
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> \endverbatim
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>
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> \param[out] DNM2
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> \verbatim
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> DNM2 is DOUBLE PRECISION
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> d(N0-2).
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> \endverbatim
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Authors:
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========
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> \author Univ. of Tennessee
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> \author Univ. of California Berkeley
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> \author Univ. of Colorado Denver
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> \author NAG Ltd.
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> \date September 2012
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> \ingroup auxOTHERcomputational
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=====================================================================
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Subroutine */ int igraphdlasq6_(integer *i0, integer *n0, doublereal *z__,
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integer *pp, doublereal *dmin__, doublereal *dmin1, doublereal *dmin2,
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doublereal *dn, doublereal *dnm1, doublereal *dnm2)
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{
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/* System generated locals */
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integer i__1;
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doublereal d__1, d__2;
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/* Local variables */
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doublereal d__;
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integer j4, j4p2;
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doublereal emin, temp;
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extern doublereal igraphdlamch_(char *);
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doublereal safmin;
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/* -- LAPACK computational routine (version 3.4.2) --
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-- LAPACK is a software package provided by Univ. of Tennessee, --
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-- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
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September 2012
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=====================================================================
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Parameter adjustments */
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--z__;
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/* Function Body */
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if (*n0 - *i0 - 1 <= 0) {
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return 0;
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}
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safmin = igraphdlamch_("Safe minimum");
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j4 = (*i0 << 2) + *pp - 3;
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emin = z__[j4 + 4];
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d__ = z__[j4];
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*dmin__ = d__;
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if (*pp == 0) {
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i__1 = *n0 - 3 << 2;
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for (j4 = *i0 << 2; j4 <= i__1; j4 += 4) {
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z__[j4 - 2] = d__ + z__[j4 - 1];
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if (z__[j4 - 2] == 0.) {
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z__[j4] = 0.;
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d__ = z__[j4 + 1];
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*dmin__ = d__;
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emin = 0.;
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} else if (safmin * z__[j4 + 1] < z__[j4 - 2] && safmin * z__[j4
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- 2] < z__[j4 + 1]) {
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temp = z__[j4 + 1] / z__[j4 - 2];
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z__[j4] = z__[j4 - 1] * temp;
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d__ *= temp;
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} else {
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z__[j4] = z__[j4 + 1] * (z__[j4 - 1] / z__[j4 - 2]);
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d__ = z__[j4 + 1] * (d__ / z__[j4 - 2]);
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}
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*dmin__ = min(*dmin__,d__);
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/* Computing MIN */
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d__1 = emin, d__2 = z__[j4];
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emin = min(d__1,d__2);
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/* L10: */
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}
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} else {
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i__1 = *n0 - 3 << 2;
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for (j4 = *i0 << 2; j4 <= i__1; j4 += 4) {
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z__[j4 - 3] = d__ + z__[j4];
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if (z__[j4 - 3] == 0.) {
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z__[j4 - 1] = 0.;
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d__ = z__[j4 + 2];
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*dmin__ = d__;
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emin = 0.;
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} else if (safmin * z__[j4 + 2] < z__[j4 - 3] && safmin * z__[j4
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- 3] < z__[j4 + 2]) {
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temp = z__[j4 + 2] / z__[j4 - 3];
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z__[j4 - 1] = z__[j4] * temp;
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d__ *= temp;
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} else {
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z__[j4 - 1] = z__[j4 + 2] * (z__[j4] / z__[j4 - 3]);
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d__ = z__[j4 + 2] * (d__ / z__[j4 - 3]);
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}
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*dmin__ = min(*dmin__,d__);
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/* Computing MIN */
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d__1 = emin, d__2 = z__[j4 - 1];
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emin = min(d__1,d__2);
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/* L20: */
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}
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}
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/* Unroll last two steps. */
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*dnm2 = d__;
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*dmin2 = *dmin__;
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j4 = (*n0 - 2 << 2) - *pp;
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j4p2 = j4 + (*pp << 1) - 1;
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z__[j4 - 2] = *dnm2 + z__[j4p2];
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if (z__[j4 - 2] == 0.) {
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z__[j4] = 0.;
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*dnm1 = z__[j4p2 + 2];
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*dmin__ = *dnm1;
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emin = 0.;
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} else if (safmin * z__[j4p2 + 2] < z__[j4 - 2] && safmin * z__[j4 - 2] <
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z__[j4p2 + 2]) {
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temp = z__[j4p2 + 2] / z__[j4 - 2];
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z__[j4] = z__[j4p2] * temp;
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*dnm1 = *dnm2 * temp;
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} else {
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z__[j4] = z__[j4p2 + 2] * (z__[j4p2] / z__[j4 - 2]);
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*dnm1 = z__[j4p2 + 2] * (*dnm2 / z__[j4 - 2]);
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}
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*dmin__ = min(*dmin__,*dnm1);
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*dmin1 = *dmin__;
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j4 += 4;
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j4p2 = j4 + (*pp << 1) - 1;
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z__[j4 - 2] = *dnm1 + z__[j4p2];
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if (z__[j4 - 2] == 0.) {
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z__[j4] = 0.;
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*dn = z__[j4p2 + 2];
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*dmin__ = *dn;
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emin = 0.;
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} else if (safmin * z__[j4p2 + 2] < z__[j4 - 2] && safmin * z__[j4 - 2] <
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z__[j4p2 + 2]) {
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temp = z__[j4p2 + 2] / z__[j4 - 2];
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z__[j4] = z__[j4p2] * temp;
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*dn = *dnm1 * temp;
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} else {
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z__[j4] = z__[j4p2 + 2] * (z__[j4p2] / z__[j4 - 2]);
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*dn = z__[j4p2 + 2] * (*dnm1 / z__[j4 - 2]);
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}
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*dmin__ = min(*dmin__,*dn);
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z__[j4 + 2] = *dn;
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z__[(*n0 << 2) - *pp] = emin;
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return 0;
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/* End of DLASQ6 */
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} /* igraphdlasq6_ */
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