1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
|
/*
* The Great Computer Language Shootout
* http://shootout.alioth.debian.org/
*
* contributed by Christoph Bauer
*
*/
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#define pi 3.141592653589793
#define solar_mass (4 * pi * pi)
#define days_per_year 365.24
struct planet {
double x, y, z;
double vx, vy, vz;
double mass;
};
void advance(int nbodies, struct planet * bodies, double dt)
{
int i, j;
for (i = 0; i < nbodies; i++) {
struct planet * b = &(bodies[i]);
for (j = i + 1; j < nbodies; j++) {
struct planet * b2 = &(bodies[j]);
double dx = b->x - b2->x;
double dy = b->y - b2->y;
double dz = b->z - b2->z;
double distance = sqrt(dx * dx + dy * dy + dz * dz);
double mag = dt / (distance * distance * distance);
b->vx -= dx * b2->mass * mag;
b->vy -= dy * b2->mass * mag;
b->vz -= dz * b2->mass * mag;
b2->vx += dx * b->mass * mag;
b2->vy += dy * b->mass * mag;
b2->vz += dz * b->mass * mag;
}
}
for (i = 0; i < nbodies; i++) {
struct planet * b = &(bodies[i]);
b->x += dt * b->vx;
b->y += dt * b->vy;
b->z += dt * b->vz;
}
}
double energy(int nbodies, struct planet * bodies)
{
double e;
int i, j;
e = 0.0;
for (i = 0; i < nbodies; i++) {
struct planet * b = &(bodies[i]);
e += 0.5 * b->mass * (b->vx * b->vx + b->vy * b->vy + b->vz * b->vz);
for (j = i + 1; j < nbodies; j++) {
struct planet * b2 = &(bodies[j]);
double dx = b->x - b2->x;
double dy = b->y - b2->y;
double dz = b->z - b2->z;
double distance = sqrt(dx * dx + dy * dy + dz * dz);
e -= (b->mass * b2->mass) / distance;
}
}
return e;
}
void offset_momentum(int nbodies, struct planet * bodies)
{
double px = 0.0, py = 0.0, pz = 0.0;
int i;
for (i = 0; i < nbodies; i++) {
px += bodies[i].vx * bodies[i].mass;
py += bodies[i].vy * bodies[i].mass;
pz += bodies[i].vz * bodies[i].mass;
}
bodies[0].vx = - px / solar_mass;
bodies[0].vy = - py / solar_mass;
bodies[0].vz = - pz / solar_mass;
}
#define NBODIES 5
struct planet bodies[NBODIES] = {
{ /* sun */
0, 0, 0, 0, 0, 0, 1.0 /*solar_mass*/
},
{ /* jupiter */
4.84143144246472090e+00,
-1.16032004402742839e+00,
-1.03622044471123109e-01,
1.66007664274403694e-03 /* * days_per_year */,
7.69901118419740425e-03 /* * days_per_year */,
-6.90460016972063023e-05 /* * days_per_year */,
9.54791938424326609e-04 /* * solar_mass */
},
{ /* saturn */
8.34336671824457987e+00,
4.12479856412430479e+00,
-4.03523417114321381e-01,
-2.76742510726862411e-03 /* * days_per_year */,
4.99852801234917238e-03 /* * days_per_year */,
2.30417297573763929e-05 /* * days_per_year */,
2.85885980666130812e-04 /* * solar_mass */
},
{ /* uranus */
1.28943695621391310e+01,
-1.51111514016986312e+01,
-2.23307578892655734e-01,
2.96460137564761618e-03 /* * days_per_year */,
2.37847173959480950e-03 /* * days_per_year */,
-2.96589568540237556e-05 /* * days_per_year */,
4.36624404335156298e-05 /* * solar_mass */
},
{ /* neptune */
1.53796971148509165e+01,
-2.59193146099879641e+01,
1.79258772950371181e-01,
2.68067772490389322e-03 /* * days_per_year */,
1.62824170038242295e-03 /* * days_per_year */,
-9.51592254519715870e-05 /* * days_per_year */,
5.15138902046611451e-05 /* * solar_mass */
}
};
void setup_bodies(void)
{
int i;
for (i = 0; i < NBODIES; i++) {
bodies[i].vx *= days_per_year;
bodies[i].vy *= days_per_year;
bodies[i].vz *= days_per_year;
bodies[i].mass *= solar_mass;
}
}
int main(int argc, char ** argv)
{
int n = argc < 2 ? 20000000 : atoi(argv[1]);
int i;
setup_bodies();
offset_momentum(NBODIES, bodies);
printf ("%.9f\n", energy(NBODIES, bodies));
for (i = 1; i <= n; i++)
advance(NBODIES, bodies, 0.01);
printf ("%.9f\n", energy(NBODIES, bodies));
return 0;
}
/***
build & benchmark results
BUILD COMMANDS FOR: nbody.gcc
Thu Jul 27 22:22:05 PDT 2006
/usr/bin/gcc -pipe -Wall -O3 -fomit-frame-pointer -funroll-loops -march=pentium4 -lm nbody.c -o nbody.gcc_run
=================================================================
COMMAND LINE (%A is single numeric argument):
nbody.gcc_run %A
N=200000 2000000 20000000
PROGRAM OUTPUT
==============
-0.169075164
-0.169031665
***/
|
