ergo
template_blas_nrm2.h
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1/* Ergo, version 3.8.2, a program for linear scaling electronic structure
2 * calculations.
3 * Copyright (C) 2023 Elias Rudberg, Emanuel H. Rubensson, Pawel Salek,
4 * and Anastasia Kruchinina.
5 *
6 * This program is free software: you can redistribute it and/or modify
7 * it under the terms of the GNU General Public License as published by
8 * the Free Software Foundation, either version 3 of the License, or
9 * (at your option) any later version.
10 *
11 * This program is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 * GNU General Public License for more details.
15 *
16 * You should have received a copy of the GNU General Public License
17 * along with this program. If not, see <http://www.gnu.org/licenses/>.
18 *
19 * Primary academic reference:
20 * Ergo: An open-source program for linear-scaling electronic structure
21 * calculations,
22 * Elias Rudberg, Emanuel H. Rubensson, Pawel Salek, and Anastasia
23 * Kruchinina,
24 * SoftwareX 7, 107 (2018),
25 * <http://dx.doi.org/10.1016/j.softx.2018.03.005>
26 *
27 * For further information about Ergo, see <http://www.ergoscf.org>.
28 */
29
30 /* This file belongs to the template_lapack part of the Ergo source
31 * code. The source files in the template_lapack directory are modified
32 * versions of files originally distributed as CLAPACK, see the
33 * Copyright/license notice in the file template_lapack/COPYING.
34 */
35
36
37#ifndef TEMPLATE_BLAS_NRM2_HEADER
38#define TEMPLATE_BLAS_NRM2_HEADER
39
40
41template<class Treal>
42Treal template_blas_nrm2(const integer *n, const Treal *x, const integer *incx)
43{
44/* The following loop is equivalent to this call to the LAPACK
45 auxiliary routine:
46 CALL DLASSQ( N, X, INCX, SCALE, SSQ ) */
47 /* System generated locals */
48 integer i__1, i__2;
49 Treal ret_val, d__1;
50 /* Local variables */
51 Treal norm, scale, absxi;
52 integer ix;
53 Treal ssq;
54/* DNRM2 returns the euclidean norm of a vector via the function
55 name, so that
56 DNRM2 := sqrt( x'*x )
57 -- This version written on 25-October-1982.
58 Modified on 14-October-1993 to inline the call to DLASSQ.
59 Sven Hammarling, Nag Ltd.
60 Parameter adjustments */
61 --x;
62 /* Function Body */
63 if (*n < 1 || *incx < 1) {
64 norm = 0.;
65 } else if (*n == 1) {
66 norm = absMACRO(x[1]);
67 } else {
68 scale = 0.;
69 ssq = 1.;
70
71
72 i__1 = (*n - 1) * *incx + 1;
73 i__2 = *incx;
74 for (ix = 1; i__2 < 0 ? ix >= i__1 : ix <= i__1; ix += i__2) {
75 if (x[ix] != 0.) {
76 absxi = (d__1 = x[ix], absMACRO(d__1));
77 if (scale < absxi) {
78/* Computing 2nd power */
79 d__1 = scale / absxi;
80 ssq = ssq * (d__1 * d__1) + 1.;
81 scale = absxi;
82 } else {
83/* Computing 2nd power */
84 d__1 = absxi / scale;
85 ssq += d__1 * d__1;
86 }
87 }
88/* L10: */
89 }
90 norm = scale * template_blas_sqrt(ssq);
91 }
92
93 ret_val = norm;
94 return ret_val;
95
96/* End of DNRM2. */
97
98} /* dnrm2_ */
99
100#endif
Treal template_blas_sqrt(Treal x)
int integer
Definition: template_blas_common.h:40
#define absMACRO(x)
Definition: template_blas_common.h:47
Treal template_blas_nrm2(const integer *n, const Treal *x, const integer *incx)
Definition: template_blas_nrm2.h:42