source code
/* The Computer Language Benchmarks Game
https://salsa.debian.org/benchmarksgame-team/benchmarksgame/
contributed by Mark C. Lewis
double[] instead of Object[] by Han Kai
*/
public final class nbody {
public static void main(String[] args) {
int n = Integer.parseInt(args[0]);
NBodySystem bodies = new NBodySystem();
System.out.printf("%.9f\n", bodies.energy());
for (int i = 0; i < n; ++i)
bodies.advance(0.01);
System.out.printf("%.9f\n", bodies.energy());
}
final static class NBodySystem {
private static final double PI = 3.141592653589793;
private static final double SOLAR_MASS = 4 * PI * PI;
private static final double DAYS_PER_YEAR = 365.24;
private static final int BODY_SIZE = 8;
private static final int BODY_COUNT = 5;
private static final int x = 0;
private static final int y = 1;
private static final int z = 2;
private static final int vx = 3;
private static final int vy = 4;
private static final int vz = 5;
private static final int mass = 6;
private final double[] _bodies = {
//sun begin
0, 0, 0, 0, 0, 0, SOLAR_MASS, 0,
//sun end
//jupiter begin
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,//
0,
//jupiter end
//saturn begin
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,//
0,
//saturn end
//uranus begin
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,//
0,
//uranus end
//neptune begin
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, //
0
//neptune end
};
public NBodySystem() {
double px = 0.0;
double py = 0.0;
double pz = 0.0;
for (int i = 0; i < BODY_COUNT; ++i) {
final int ioffset = BODY_SIZE * i;
double imass = _bodies[ioffset + mass];
px += _bodies[ioffset + vx] * imass;
py += _bodies[ioffset + vy] * imass;
pz += _bodies[ioffset + vz] * imass;
}
_bodies[vx] = -px / SOLAR_MASS;
_bodies[vy] = -py / SOLAR_MASS;
_bodies[vz] = -pz / SOLAR_MASS;
}
public void advance(double dt) {
final double[] bodies = _bodies;
for (int i = 0; i < BODY_COUNT; ++i) {
final int offset = BODY_SIZE * i;
for (int j = i + 1; j < BODY_COUNT; ++j) {
final int ioffset = offset;
final int joffset = BODY_SIZE * j;
final double dx = bodies[ioffset + x] - bodies[joffset + x];
final double dy = bodies[ioffset + y] - bodies[joffset + y];
final double dz = bodies[ioffset + z] - bodies[joffset + z];
final double dSquared = dx * dx + dy * dy + dz * dz;
final double distance = Math.sqrt(dSquared);
final double mag = dt / (dSquared * distance);
final double jmass = bodies[joffset + mass];
bodies[ioffset + vx] -= dx * jmass * mag;
bodies[ioffset + vy] -= dy * jmass * mag;
bodies[ioffset + vz] -= dz * jmass * mag;
final double imass = bodies[ioffset + mass];
bodies[joffset + vx] += dx * imass * mag;
bodies[joffset + vy] += dy * imass * mag;
bodies[joffset + vz] += dz * imass * mag;
}
}
for (int i = 0; i < BODY_COUNT; ++i) {
final int ioffset = BODY_SIZE * i;
bodies[ioffset + x] += dt * bodies[ioffset + vx];
bodies[ioffset + y] += dt * bodies[ioffset + vy];
bodies[ioffset + z] += dt * bodies[ioffset + vz];
}
}
public double energy() {
final double[] bodies = _bodies;
double dx, dy, dz, distance;
double e = 0.0;
for (int i = 0; i < BODY_COUNT; ++i) {
final int offset = BODY_SIZE * i;
final double ivx = bodies[offset + vx];
final double ivy = bodies[offset + vy];
final double ivz = bodies[offset + vz];
final double imass = bodies[offset + mass];
e += 0.5 * imass * (ivx * ivx + ivy * ivy + ivz * ivz);
for (int j = i + 1; j < BODY_COUNT; ++j) {
final int ioffset = offset;
final int joffset = BODY_SIZE * j;
final double ix = bodies[ioffset + x];
final double iy = bodies[ioffset + y];
final double iz = bodies[ioffset + z];
dx = ix - bodies[joffset + x];
dy = iy - bodies[joffset + y];
dz = iz - bodies[joffset + z];
distance = Math.sqrt(dx * dx + dy * dy + dz * dz);
e -= (imass * bodies[joffset + mass]) / distance;
}
}
return e;
}
}
}
notes, command-line, and program output
NOTES:
64-bit Ubuntu quad core
java 23 2024-09-17
Java HotSpot(TM) 64-Bit Server VM
(build 23+37-2369,
interpreted mode, sharing)
Fri, 20 Sep 2024 05:07:48 GMT
MAKE:
mv nbody.javaxint-5.javaxint nbody.java
/opt/src/jdk-23/bin/javac -d . -cp . nbody.java
1.74s to complete and log all make actions
COMMAND LINE:
/opt/src/jdk-23/bin/java -Xint -cp . nbody 50000000
PROGRAM OUTPUT:
-0.169075164
-0.169059907