ergo
template_lapack_ladiv.h
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1 /* Ergo, version 3.2, a program for linear scaling electronic structure
2  * calculations.
3  * Copyright (C) 2012 Elias Rudberg, Emanuel H. Rubensson, and Pawel Salek.
4  *
5  * This program is free software: you can redistribute it and/or modify
6  * it under the terms of the GNU General Public License as published by
7  * the Free Software Foundation, either version 3 of the License, or
8  * (at your option) any later version.
9  *
10  * This program is distributed in the hope that it will be useful,
11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13  * GNU General Public License for more details.
14  *
15  * You should have received a copy of the GNU General Public License
16  * along with this program. If not, see <http://www.gnu.org/licenses/>.
17  *
18  * Primary academic reference:
19  * Kohn−Sham Density Functional Theory Electronic Structure Calculations
20  * with Linearly Scaling Computational Time and Memory Usage,
21  * Elias Rudberg, Emanuel H. Rubensson, and Pawel Salek,
22  * J. Chem. Theory Comput. 7, 340 (2011),
23  * <http://dx.doi.org/10.1021/ct100611z>
24  *
25  * For further information about Ergo, see <http://www.ergoscf.org>.
26  */
27 
28  /* This file belongs to the template_lapack part of the Ergo source
29  * code. The source files in the template_lapack directory are modified
30  * versions of files originally distributed as CLAPACK, see the
31  * Copyright/license notice in the file template_lapack/COPYING.
32  */
33 
34 
35 #ifndef TEMPLATE_LAPACK_LADIV_HEADER
36 #define TEMPLATE_LAPACK_LADIV_HEADER
37 
38 
39 template<class Treal>
40 int template_lapack_ladiv(const Treal *a, const Treal *b, const Treal *c__,
41  const Treal *d__, Treal *p, Treal *q)
42 {
43 /* -- LAPACK auxiliary routine (version 3.0) --
44  Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,
45  Courant Institute, Argonne National Lab, and Rice University
46  October 31, 1992
47 
48 
49  Purpose
50  =======
51 
52  DLADIV performs complex division in real arithmetic
53 
54  a + i*b
55  p + i*q = ---------
56  c + i*d
57 
58  The algorithm is due to Robert L. Smith and can be found
59  in D. Knuth, The art of Computer Programming, Vol.2, p.195
60 
61  Arguments
62  =========
63 
64  A (input) DOUBLE PRECISION
65  B (input) DOUBLE PRECISION
66  C (input) DOUBLE PRECISION
67  D (input) DOUBLE PRECISION
68  The scalars a, b, c, and d in the above expression.
69 
70  P (output) DOUBLE PRECISION
71  Q (output) DOUBLE PRECISION
72  The scalars p and q in the above expression.
73 
74  ===================================================================== */
75  Treal e, f;
76 
77 
78 
79  if (absMACRO(*d__) < absMACRO(*c__)) {
80  e = *d__ / *c__;
81  f = *c__ + *d__ * e;
82  *p = (*a + *b * e) / f;
83  *q = (*b - *a * e) / f;
84  } else {
85  e = *c__ / *d__;
86  f = *d__ + *c__ * e;
87  *p = (*b + *a * e) / f;
88  *q = (-(*a) + *b * e) / f;
89  }
90 
91  return 0;
92 
93 /* End of DLADIV */
94 
95 } /* dladiv_ */
96 
97 #endif