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| 1 | +import java.util.Locale; |
| 2 | + |
| 3 | +public class Nbody { |
| 4 | + static final double PI = 3.141592653589793; |
| 5 | + static final double SOLAR_MASS = 4 * PI * PI; |
| 6 | + static final double DAYS = 365.24; |
| 7 | + static final double[] x = {0.0, 4.84143144246472090e+00, 8.34336671824457987e+00, 1.28943695621391310e+01, 1.53796971148509165e+01}; |
| 8 | + static final double[] y = {0.0, -1.16032004402742839e+00, 4.12479856412430479e+00, -1.51111514016986312e+01, -2.59193146099879641e+01}; |
| 9 | + static final double[] z = {0.0, -1.03622044471123109e-01, -4.03523417114321381e-01, -2.23307578892655734e-01, 1.79258772950371181e-01}; |
| 10 | + static final double[] vx = {0.0, 1.66007664274403694e-03 * DAYS, -2.76742510726862411e-03 * DAYS, 2.96460137564761618e-03 * DAYS, 2.68067772490389322e-03 * DAYS}; |
| 11 | + static final double[] vy = {0.0, 7.69901118419740425e-03 * DAYS, 4.99852801234917238e-03 * DAYS, 2.37847173959480950e-03 * DAYS, 1.62824170038242295e-03 * DAYS}; |
| 12 | + static final double[] vz = {0.0, -6.90460016972063023e-05 * DAYS, 2.30417297573763929e-05 * DAYS, -2.96589568540237556e-05 * DAYS, -9.51592254519715870e-05 * DAYS}; |
| 13 | + static final double[] mass = {SOLAR_MASS, 9.54791938424326609e-04 * SOLAR_MASS, 2.85885980666130812e-04 * SOLAR_MASS, 4.36624404335156298e-05 * SOLAR_MASS, 5.15138902046611451e-05 * SOLAR_MASS}; |
| 14 | + |
| 15 | + static void offsetMomentum() { |
| 16 | + double px = 0.0, py = 0.0, pz = 0.0; |
| 17 | + for (int i = 0; i < 5; i++) { |
| 18 | + px += vx[i] * mass[i]; |
| 19 | + py += vy[i] * mass[i]; |
| 20 | + pz += vz[i] * mass[i]; |
| 21 | + } |
| 22 | + vx[0] = -px / SOLAR_MASS; |
| 23 | + vy[0] = -py / SOLAR_MASS; |
| 24 | + vz[0] = -pz / SOLAR_MASS; |
| 25 | + } |
| 26 | + |
| 27 | + static void advance(double dt, int steps) { |
| 28 | + for (int s = 0; s < steps; s++) { |
| 29 | + for (int i = 0; i < 5; i++) { |
| 30 | + for (int j = i + 1; j < 5; j++) { |
| 31 | + double dx = x[i] - x[j]; |
| 32 | + double dy = y[i] - y[j]; |
| 33 | + double dz = z[i] - z[j]; |
| 34 | + double d2 = dx * dx + dy * dy + dz * dz; |
| 35 | + double mag = dt / (d2 * Math.sqrt(d2)); |
| 36 | + vx[i] -= dx * mass[j] * mag; |
| 37 | + vy[i] -= dy * mass[j] * mag; |
| 38 | + vz[i] -= dz * mass[j] * mag; |
| 39 | + vx[j] += dx * mass[i] * mag; |
| 40 | + vy[j] += dy * mass[i] * mag; |
| 41 | + vz[j] += dz * mass[i] * mag; |
| 42 | + } |
| 43 | + } |
| 44 | + for (int i = 0; i < 5; i++) { |
| 45 | + x[i] += dt * vx[i]; |
| 46 | + y[i] += dt * vy[i]; |
| 47 | + z[i] += dt * vz[i]; |
| 48 | + } |
| 49 | + } |
| 50 | + } |
| 51 | + |
| 52 | + static double energy() { |
| 53 | + double e = 0.0; |
| 54 | + for (int i = 0; i < 5; i++) { |
| 55 | + e += 0.5 * mass[i] * (vx[i] * vx[i] + vy[i] * vy[i] + vz[i] * vz[i]); |
| 56 | + for (int j = i + 1; j < 5; j++) { |
| 57 | + double dx = x[i] - x[j]; |
| 58 | + double dy = y[i] - y[j]; |
| 59 | + double dz = z[i] - z[j]; |
| 60 | + e -= mass[i] * mass[j] / Math.sqrt(dx * dx + dy * dy + dz * dz); |
| 61 | + } |
| 62 | + } |
| 63 | + return e; |
| 64 | + } |
| 65 | + |
| 66 | + public static void main(String[] args) { |
| 67 | + int n = Integer.parseInt(args[0]); |
| 68 | + offsetMomentum(); |
| 69 | + double before = energy(); |
| 70 | + advance(0.01, n); |
| 71 | + double after = energy(); |
| 72 | + System.out.println(String.format(Locale.ROOT, "%.9f %.9f", before, after)); |
| 73 | + } |
| 74 | +} |
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