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/* Ergo, version 3.8.2, a program for linear scaling electronic structure
* calculations.
* Copyright (C) 2023 Elias Rudberg, Emanuel H. Rubensson, Pawel Salek,
* and Anastasia Kruchinina.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
* Primary academic reference:
* Ergo: An open-source program for linear-scaling electronic structure
* calculations,
* Elias Rudberg, Emanuel H. Rubensson, Pawel Salek, and Anastasia
* Kruchinina,
* SoftwareX 7, 107 (2018),
* <http://dx.doi.org/10.1016/j.softx.2018.03.005>
*
* For further information about Ergo, see <http://www.ergoscf.org>.
*/
/* This file belongs to the template_lapack part of the Ergo source
* code. The source files in the template_lapack directory are modified
* versions of files originally distributed as CLAPACK, see the
* Copyright/license notice in the file template_lapack/COPYING.
*/
#ifndef TEMPLATE_LAPACK_LARTG_HEADER
#define TEMPLATE_LAPACK_LARTG_HEADER
template<class Treal>
int template_lapack_lartg(const Treal *f, const Treal *g, Treal *cs,
Treal *sn, Treal *r__)
{
/* -- LAPACK auxiliary routine (version 3.0) --
Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,
Courant Institute, Argonne National Lab, and Rice University
September 30, 1994
Purpose
=======
DLARTG generate a plane rotation so that
[ CS SN ] . [ F ] = [ R ] where CS**2 + SN**2 = 1.
[ -SN CS ] [ G ] [ 0 ]
This is a slower, more accurate version of the BLAS1 routine DROTG,
with the following other differences:
F and G are unchanged on return.
If G=0, then CS=1 and SN=0.
If F=0 and (G .ne. 0), then CS=0 and SN=1 without doing any
floating point operations (saves work in DBDSQR when
there are zeros on the diagonal).
If F exceeds G in magnitude, CS will be positive.
Arguments
=========
F (input) DOUBLE PRECISION
The first component of vector to be rotated.
G (input) DOUBLE PRECISION
The second component of vector to be rotated.
CS (output) DOUBLE PRECISION
The cosine of the rotation.
SN (output) DOUBLE PRECISION
The sine of the rotation.
R (output) DOUBLE PRECISION
The nonzero component of the rotated vector.
===================================================================== */
/* Initialized data */
logical first = TRUE_;
/* System generated locals */
integer i__1;
Treal d__1, d__2;
/* Local variables */
integer i__;
Treal scale;
integer count;
Treal f1, g1, safmn2, safmx2;
Treal safmin, eps;
if (first) {
first = FALSE_;
safmin = template_lapack_lamch("S", (Treal)0);
eps = template_lapack_lamch("E", (Treal)0);
d__1 = template_lapack_lamch("B", (Treal)0);
i__1 = (integer) (template_blas_log(safmin / eps) / template_blas_log(template_lapack_lamch("B", (Treal)0)) /
2.);
safmn2 = template_lapack_pow_di(&d__1, &i__1);
safmx2 = 1. / safmn2;
}
if (*g == 0.) {
*cs = 1.;
*sn = 0.;
*r__ = *f;
} else if (*f == 0.) {
*cs = 0.;
*sn = 1.;
*r__ = *g;
} else {
f1 = *f;
g1 = *g;
/* Computing MAX */
d__1 = absMACRO(f1), d__2 = absMACRO(g1);
scale = maxMACRO(d__1,d__2);
if (scale >= safmx2) {
count = 0;
L10:
++count;
f1 *= safmn2;
g1 *= safmn2;
/* Computing MAX */
d__1 = absMACRO(f1), d__2 = absMACRO(g1);
scale = maxMACRO(d__1,d__2);
if (scale >= safmx2) {
goto L10;
}
/* Computing 2nd power */
d__1 = f1;
/* Computing 2nd power */
d__2 = g1;
*r__ = template_blas_sqrt(d__1 * d__1 + d__2 * d__2);
*cs = f1 / *r__;
*sn = g1 / *r__;
i__1 = count;
for (i__ = 1; i__ <= i__1; ++i__) {
*r__ *= safmx2;
/* L20: */
}
} else if (scale <= safmn2) {
count = 0;
L30:
++count;
f1 *= safmx2;
g1 *= safmx2;
/* Computing MAX */
d__1 = absMACRO(f1), d__2 = absMACRO(g1);
scale = maxMACRO(d__1,d__2);
if (scale <= safmn2) {
goto L30;
}
/* Computing 2nd power */
d__1 = f1;
/* Computing 2nd power */
d__2 = g1;
*r__ = template_blas_sqrt(d__1 * d__1 + d__2 * d__2);
*cs = f1 / *r__;
*sn = g1 / *r__;
i__1 = count;
for (i__ = 1; i__ <= i__1; ++i__) {
*r__ *= safmn2;
/* L40: */
}
} else {
/* Computing 2nd power */
d__1 = f1;
/* Computing 2nd power */
d__2 = g1;
*r__ = template_blas_sqrt(d__1 * d__1 + d__2 * d__2);
*cs = f1 / *r__;
*sn = g1 / *r__;
}
if (absMACRO(*f) > absMACRO(*g) && *cs < 0.) {
*cs = -(*cs);
*sn = -(*sn);
*r__ = -(*r__);
}
}
return 0;
/* End of DLARTG */
} /* dlartg_ */
#endif
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