EvtGen 2.2.0
Monte Carlo generator of particle decays, in particular the weak decays of heavy flavour particles such as B mesons.
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EvtLi2Spence.cpp
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1
2/***********************************************************************
3* Copyright 1998-2020 CERN for the benefit of the EvtGen authors *
4* *
5* This file is part of EvtGen. *
6* *
7* EvtGen is free software: you can redistribute it and/or modify *
8* it under the terms of the GNU General Public License as published by *
9* the Free Software Foundation, either version 3 of the License, or *
10* (at your option) any later version. *
11* *
12* EvtGen is distributed in the hope that it will be useful, *
13* but WITHOUT ANY WARRANTY; without even the implied warranty of *
14* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the *
15* GNU General Public License for more details. *
16* *
17* You should have received a copy of the GNU General Public License *
18* along with EvtGen. If not, see <https://www.gnu.org/licenses/>. *
19***********************************************************************/
20
21#include <math.h>
22
23const double a1 = -0.250000000000000;
24const double a2 = -0.111111111111111;
25const double a3 = -0.010000000000000;
26const double a4 = -0.017006802721088;
27const double a5 = -0.019444444444444;
28const double a6 = -0.020661157024793;
29const double a7 = -0.021417300648069;
30const double a8 = -0.021948866377231;
31const double a9 = -0.022349233811171;
32const double a10 = -0.022663689135191;
33const double zeta2 = 1.644934066848226;
34
35double li2spence( double x )
36{
37 double result = 0;
38 double xr = x;
39 double xi = 0;
40 double r2 = xr * xr + xi * xi;
41
42 double y, z, z2, sp;
43
44 if ( r2 > 1. && ( xr / r2 ) > 0.5 ) {
45 y = ( x - 1.0 ) / x;
46 z = -log( 1.0 - y );
47 z2 = z * z;
48 sp =
49 z * ( 1.0 +
50 a1 * z *
51 ( 1.0 +
52 a2 * z *
53 ( 1.0 +
54 a3 * z2 *
55 ( 1.0 +
56 a4 * z2 *
57 ( 1.0 +
58 a5 * z2 *
59 ( 1.0 +
60 a6 * z2 *
61 ( 1.0 +
62 a7 * z2 *
63 ( 1.0 +
64 a8 * z2 *
65 ( 1.0 +
66 a9 * z2 *
67 ( 1.0 +
68 a10 * z2 ) ) ) ) ) ) ) ) ) ) +
69 zeta2 - log( x ) * log( 1.0 - x ) + 0.5 * log( x ) * log( x );
70 result = sp;
71
72 } else if ( r2 > 1 && ( xr / r2 ) <= 0.5 ) {
73 y = 1.0 / x;
74 z = -log( 1.0 - y );
75 z2 = z * z;
76 sp =
77 -z *
78 ( 1.0 +
79 a1 * z *
80 ( 1.0 +
81 a2 * z *
82 ( 1.0 +
83 a3 * z2 *
84 ( 1.0 +
85 a4 * z2 *
86 ( 1.0 +
87 a5 * z2 *
88 ( 1.0 +
89 a6 * z2 *
90 ( 1.0 +
91 a7 * z2 *
92 ( 1.0 +
93 a8 * z2 *
94 ( 1.0 +
95 a9 * z2 *
96 ( 1.0 +
97 a10 * z2 ) ) ) ) ) ) ) ) ) ) +
98 zeta2 - 0.5 * log( -x ) * log( -x );
99 result = sp;
100
101 } else if ( r2 == 1 && xi == 0 ) {
102 sp = zeta2;
103 result = sp;
104
105 } else if ( r2 <= 1 && xr > 0.5 ) {
106 y = 1.0 - x;
107 z = -log( 1.0 - y );
108 z2 = z * z;
109 sp =
110 -z *
111 ( 1.0 +
112 a1 * z *
113 ( 1.0 +
114 a2 * z *
115 ( 1.0 +
116 a3 * z2 *
117 ( 1.0 +
118 a4 * z2 *
119 ( 1.0 +
120 a5 * z2 *
121 ( 1.0 +
122 a6 * z2 *
123 ( 1.0 +
124 a7 * z2 *
125 ( 1.0 +
126 a8 * z2 *
127 ( 1.0 +
128 a9 * z2 *
129 ( 1.0 +
130 a10 * z2 ) ) ) ) ) ) ) ) ) ) +
131 zeta2 - log( x ) * log( 1.0 - x );
132 result = sp;
133
134 } else if ( r2 <= 1 && xr <= 0.5 ) {
135 y = x;
136 z = -log( 1.0 - y );
137 z2 = z * z;
138 sp =
139 z *
140 ( 1.0 +
141 a1 * z *
142 ( 1.0 +
143 a2 * z *
144 ( 1.0 +
145 a3 * z2 *
146 ( 1.0 +
147 a4 * z2 *
148 ( 1.0 +
149 a5 * z2 *
150 ( 1.0 +
151 a6 * z2 *
152 ( 1.0 +
153 a7 * z2 *
154 ( 1.0 +
155 a8 * z2 *
156 ( 1.0 +
157 a9 * z2 *
158 ( 1.0 +
159 a10 * z2 ) ) ) ) ) ) ) ) ) );
160 result = sp;
161 }
162
163 return result;
164}
a10
const double a10
Definition EvtLi2Spence.cpp:32
a9
const double a9
Definition EvtLi2Spence.cpp:31
a4
const double a4
Definition EvtLi2Spence.cpp:26
a3
const double a3
Definition EvtLi2Spence.cpp:25
a6
const double a6
Definition EvtLi2Spence.cpp:28
a8
const double a8
Definition EvtLi2Spence.cpp:30
a5
const double a5
Definition EvtLi2Spence.cpp:27
a2
const double a2
Definition EvtLi2Spence.cpp:24
li2spence
double li2spence(double x)
Definition EvtLi2Spence.cpp:35
zeta2
const double zeta2
Definition EvtLi2Spence.cpp:33
a7
const double a7
Definition EvtLi2Spence.cpp:29
a1
const double a1
Definition EvtLi2Spence.cpp:23
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