/* -- translated by f2c (version 20100827).
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*/
#include "f2c.h"
/* > \brief \b DLASQ6 computes one dqd transform in ping-pong form. Used by sbdsqr and sstegr.
=========== DOCUMENTATION ===========
Online html documentation available at
http://www.netlib.org/lapack/explore-html/
> \htmlonly
> Download DLASQ6 + dependencies
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f">
> [TGZ]</a>
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f">
> [ZIP]</a>
> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/dlasq6.
f">
> [TXT]</a>
> \endhtmlonly
Definition:
===========
SUBROUTINE DLASQ6( I0, N0, Z, PP, DMIN, DMIN1, DMIN2, DN,
DNM1, DNM2 )
INTEGER I0, N0, PP
DOUBLE PRECISION DMIN, DMIN1, DMIN2, DN, DNM1, DNM2
DOUBLE PRECISION Z( * )
> \par Purpose:
=============
>
> \verbatim
>
> DLASQ6 computes one dqd (shift equal to zero) transform in
> ping-pong form, with protection against underflow and overflow.
> \endverbatim
Arguments:
==========
> \param[in] I0
> \verbatim
> I0 is INTEGER
> First index.
> \endverbatim
>
> \param[in] N0
> \verbatim
> N0 is INTEGER
> Last index.
> \endverbatim
>
> \param[in] Z
> \verbatim
> Z is DOUBLE PRECISION array, dimension ( 4*N )
> Z holds the qd array. EMIN is stored in Z(4*N0) to avoid
> an extra argument.
> \endverbatim
>
> \param[in] PP
> \verbatim
> PP is INTEGER
> PP=0 for ping, PP=1 for pong.
> \endverbatim
>
> \param[out] DMIN
> \verbatim
> DMIN is DOUBLE PRECISION
> Minimum value of d.
> \endverbatim
>
> \param[out] DMIN1
> \verbatim
> DMIN1 is DOUBLE PRECISION
> Minimum value of d, excluding D( N0 ).
> \endverbatim
>
> \param[out] DMIN2
> \verbatim
> DMIN2 is DOUBLE PRECISION
> Minimum value of d, excluding D( N0 ) and D( N0-1 ).
> \endverbatim
>
> \param[out] DN
> \verbatim
> DN is DOUBLE PRECISION
> d(N0), the last value of d.
> \endverbatim
>
> \param[out] DNM1
> \verbatim
> DNM1 is DOUBLE PRECISION
> d(N0-1).
> \endverbatim
>
> \param[out] DNM2
> \verbatim
> DNM2 is DOUBLE PRECISION
> d(N0-2).
> \endverbatim
Authors:
========
> \author Univ. of Tennessee
> \author Univ. of California Berkeley
> \author Univ. of Colorado Denver
> \author NAG Ltd.
> \date September 2012
> \ingroup auxOTHERcomputational
=====================================================================
Subroutine */ int igraphdlasq6_(integer *i0, integer *n0, doublereal *z__,
integer *pp, doublereal *dmin__, doublereal *dmin1, doublereal *dmin2,
doublereal *dn, doublereal *dnm1, doublereal *dnm2)
{
/* System generated locals */
integer i__1;
doublereal d__1, d__2;
/* Local variables */
doublereal d__;
integer j4, j4p2;
doublereal emin, temp;
extern doublereal igraphdlamch_(char *);
doublereal safmin;
/* -- LAPACK computational routine (version 3.4.2) --
-- LAPACK is a software package provided by Univ. of Tennessee, --
-- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
September 2012
=====================================================================
Parameter adjustments */
--z__;
/* Function Body */
if (*n0 - *i0 - 1 <= 0) {
return 0;
}
safmin = igraphdlamch_("Safe minimum");
j4 = (*i0 << 2) + *pp - 3;
emin = z__[j4 + 4];
d__ = z__[j4];
*dmin__ = d__;
if (*pp == 0) {
i__1 = *n0 - 3 << 2;
for (j4 = *i0 << 2; j4 <= i__1; j4 += 4) {
z__[j4 - 2] = d__ + z__[j4 - 1];
if (z__[j4 - 2] == 0.) {
z__[j4] = 0.;
d__ = z__[j4 + 1];
*dmin__ = d__;
emin = 0.;
} else if (safmin * z__[j4 + 1] < z__[j4 - 2] && safmin * z__[j4
- 2] < z__[j4 + 1]) {
temp = z__[j4 + 1] / z__[j4 - 2];
z__[j4] = z__[j4 - 1] * temp;
d__ *= temp;
} else {
z__[j4] = z__[j4 + 1] * (z__[j4 - 1] / z__[j4 - 2]);
d__ = z__[j4 + 1] * (d__ / z__[j4 - 2]);
}
*dmin__ = min(*dmin__,d__);
/* Computing MIN */
d__1 = emin, d__2 = z__[j4];
emin = min(d__1,d__2);
/* L10: */
}
} else {
i__1 = *n0 - 3 << 2;
for (j4 = *i0 << 2; j4 <= i__1; j4 += 4) {
z__[j4 - 3] = d__ + z__[j4];
if (z__[j4 - 3] == 0.) {
z__[j4 - 1] = 0.;
d__ = z__[j4 + 2];
*dmin__ = d__;
emin = 0.;
} else if (safmin * z__[j4 + 2] < z__[j4 - 3] && safmin * z__[j4
- 3] < z__[j4 + 2]) {
temp = z__[j4 + 2] / z__[j4 - 3];
z__[j4 - 1] = z__[j4] * temp;
d__ *= temp;
} else {
z__[j4 - 1] = z__[j4 + 2] * (z__[j4] / z__[j4 - 3]);
d__ = z__[j4 + 2] * (d__ / z__[j4 - 3]);
}
*dmin__ = min(*dmin__,d__);
/* Computing MIN */
d__1 = emin, d__2 = z__[j4 - 1];
emin = min(d__1,d__2);
/* L20: */
}
}
/* Unroll last two steps. */
*dnm2 = d__;
*dmin2 = *dmin__;
j4 = (*n0 - 2 << 2) - *pp;
j4p2 = j4 + (*pp << 1) - 1;
z__[j4 - 2] = *dnm2 + z__[j4p2];
if (z__[j4 - 2] == 0.) {
z__[j4] = 0.;
*dnm1 = z__[j4p2 + 2];
*dmin__ = *dnm1;
emin = 0.;
} else if (safmin * z__[j4p2 + 2] < z__[j4 - 2] && safmin * z__[j4 - 2] <
z__[j4p2 + 2]) {
temp = z__[j4p2 + 2] / z__[j4 - 2];
z__[j4] = z__[j4p2] * temp;
*dnm1 = *dnm2 * temp;
} else {
z__[j4] = z__[j4p2 + 2] * (z__[j4p2] / z__[j4 - 2]);
*dnm1 = z__[j4p2 + 2] * (*dnm2 / z__[j4 - 2]);
}
*dmin__ = min(*dmin__,*dnm1);
*dmin1 = *dmin__;
j4 += 4;
j4p2 = j4 + (*pp << 1) - 1;
z__[j4 - 2] = *dnm1 + z__[j4p2];
if (z__[j4 - 2] == 0.) {
z__[j4] = 0.;
*dn = z__[j4p2 + 2];
*dmin__ = *dn;
emin = 0.;
} else if (safmin * z__[j4p2 + 2] < z__[j4 - 2] && safmin * z__[j4 - 2] <
z__[j4p2 + 2]) {
temp = z__[j4p2 + 2] / z__[j4 - 2];
z__[j4] = z__[j4p2] * temp;
*dn = *dnm1 * temp;
} else {
z__[j4] = z__[j4p2 + 2] * (z__[j4p2] / z__[j4 - 2]);
*dn = z__[j4p2 + 2] * (*dnm1 / z__[j4 - 2]);
}
*dmin__ = min(*dmin__,*dn);
z__[j4 + 2] = *dn;
z__[(*n0 << 2) - *pp] = emin;
return 0;
/* End of DLASQ6 */
} /* igraphdlasq6_ */