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template_lapack_labad.h
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1 /* Ergo, version 3.7, a program for linear scaling electronic structure
2  * calculations.
3  * Copyright (C) 2018 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_LAPACK_LABAD_HEADER
38 #define TEMPLATE_LAPACK_LABAD_HEADER
39 
40 
41 template<class Treal>
42 int template_lapack_labad(Treal *small, Treal *large)
43 {
44 /* -- LAPACK auxiliary routine (version 3.0) --
45  Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,
46  Courant Institute, Argonne National Lab, and Rice University
47  October 31, 1992
48 
49 
50  Purpose
51  =======
52 
53  DLABAD takes as input the values computed by DLAMCH for underflow and
54  overflow, and returns the square root of each of these values if the
55  log of LARGE is sufficiently large. This subroutine is intended to
56  identify machines with a large exponent range, such as the Crays, and
57  redefine the underflow and overflow limits to be the square roots of
58  the values computed by DLAMCH. This subroutine is needed because
59  DLAMCH does not compensate for poor arithmetic in the upper half of
60  the exponent range, as is found on a Cray.
61 
62  Arguments
63  =========
64 
65  SMALL (input/output) DOUBLE PRECISION
66  On entry, the underflow threshold as computed by DLAMCH.
67  On exit, if LOG10(LARGE) is sufficiently large, the square
68  root of SMALL, otherwise unchanged.
69 
70  LARGE (input/output) DOUBLE PRECISION
71  On entry, the overflow threshold as computed by DLAMCH.
72  On exit, if LOG10(LARGE) is sufficiently large, the square
73  root of LARGE, otherwise unchanged.
74 
75  =====================================================================
76 
77 
78  If it looks like we're on a Cray, take the square root of
79  SMALL and LARGE to avoid overflow and underflow problems. */
80 
81 
82  if (template_blas_lg10(large) > 2e3) {
83  *small = template_blas_sqrt(*small);
84  *large = template_blas_sqrt(*large);
85  }
86 
87  return 0;
88 
89  /* End of DLABAD */
90 
91 } /* dlabad_ */
92 
93 #endif
Treal template_blas_lg10(Treal *x)
Definition: template_lapack_lamch.h:60
int template_lapack_labad(Treal *small, Treal *large)
Definition: template_lapack_labad.h:42
Treal template_blas_sqrt(Treal x)