152 lines
4.0 KiB
Rust
152 lines
4.0 KiB
Rust
// xfail-test reading from os::args()[1] - bogus!
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use std::from_str::FromStr;
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use std::os;
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static PI: f64 = 3.141592653589793;
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static SOLAR_MASS: f64 = 4.0 * PI * PI;
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static YEAR: f64 = 365.24;
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static N_BODIES: uint = 5;
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static BODIES: [Planet, ..N_BODIES] = [
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// Sun
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Planet {
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x: [ 0.0, 0.0, 0.0 ],
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v: [ 0.0, 0.0, 0.0 ],
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mass: SOLAR_MASS,
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},
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// Jupiter
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Planet {
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x: [
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4.84143144246472090e+00,
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-1.16032004402742839e+00,
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-1.03622044471123109e-01,
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],
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v: [
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1.66007664274403694e-03 * YEAR,
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7.69901118419740425e-03 * YEAR,
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-6.90460016972063023e-05 * YEAR,
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],
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mass: 9.54791938424326609e-04 * SOLAR_MASS,
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},
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// Saturn
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Planet {
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x: [
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8.34336671824457987e+00,
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4.12479856412430479e+00,
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-4.03523417114321381e-01,
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],
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v: [
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-2.76742510726862411e-03 * YEAR,
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4.99852801234917238e-03 * YEAR,
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2.30417297573763929e-05 * YEAR,
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],
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mass: 2.85885980666130812e-04 * SOLAR_MASS,
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},
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// Uranus
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Planet {
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x: [
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1.28943695621391310e+01,
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-1.51111514016986312e+01,
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-2.23307578892655734e-01,
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],
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v: [
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2.96460137564761618e-03 * YEAR,
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2.37847173959480950e-03 * YEAR,
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-2.96589568540237556e-05 * YEAR,
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],
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mass: 4.36624404335156298e-05 * SOLAR_MASS,
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},
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// Neptune
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Planet {
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x: [
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1.53796971148509165e+01,
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-2.59193146099879641e+01,
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1.79258772950371181e-01,
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],
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v: [
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2.68067772490389322e-03 * YEAR,
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1.62824170038242295e-03 * YEAR,
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-9.51592254519715870e-05 * YEAR,
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],
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mass: 5.15138902046611451e-05 * SOLAR_MASS,
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},
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];
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struct Planet {
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x: [f64, ..3],
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v: [f64, ..3],
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mass: f64,
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}
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fn advance(bodies: &mut [Planet, ..N_BODIES], dt: f64, steps: i32) {
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let mut d = [ 0.0, ..3 ];
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for _ in range(0, steps) {
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for i in range(0u, N_BODIES) {
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for j in range(i + 1, N_BODIES) {
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d[0] = bodies[i].x[0] - bodies[j].x[0];
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d[1] = bodies[i].x[1] - bodies[j].x[1];
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d[2] = bodies[i].x[2] - bodies[j].x[2];
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let d2 = d[0]*d[0] + d[1]*d[1] + d[2]*d[2];
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let mag = dt / (d2 * d2.sqrt());
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let a_mass = bodies[i].mass;
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let b_mass = bodies[j].mass;
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bodies[i].v[0] -= d[0] * b_mass * mag;
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bodies[i].v[1] -= d[1] * b_mass * mag;
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bodies[i].v[2] -= d[2] * b_mass * mag;
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bodies[j].v[0] += d[0] * a_mass * mag;
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bodies[j].v[1] += d[1] * a_mass * mag;
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bodies[j].v[2] += d[2] * a_mass * mag;
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}
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}
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for a in bodies.mut_iter() {
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a.x[0] += dt * a.v[0];
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a.x[1] += dt * a.v[1];
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a.x[2] += dt * a.v[2];
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}
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}
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}
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fn energy(bodies: &[Planet, ..N_BODIES]) -> f64 {
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let mut e = 0.0;
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let mut d = [ 0.0, ..3 ];
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for i in range(0u, N_BODIES) {
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for k in range(0u, 3) {
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e += bodies[i].mass * bodies[i].v[k] * bodies[i].v[k] / 2.0;
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}
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for j in range(i + 1, N_BODIES) {
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for k in range(0u, 3) {
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d[k] = bodies[i].x[k] - bodies[j].x[k];
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}
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let dist = (d[0]*d[0] + d[1]*d[1] + d[2]*d[2]).sqrt();
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e -= bodies[i].mass * bodies[j].mass / dist;
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}
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}
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e
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}
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fn offset_momentum(bodies: &mut [Planet, ..N_BODIES]) {
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for i in range(0u, N_BODIES) {
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for k in range(0u, 3) {
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bodies[0].v[k] -= bodies[i].v[k] * bodies[i].mass / SOLAR_MASS;
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}
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}
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}
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fn main() {
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let n: i32 = FromStr::from_str(os::args()[1]).unwrap();
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let mut bodies = BODIES;
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offset_momentum(&mut bodies);
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println!("{:.9f}", energy(&bodies) as float);
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advance(&mut bodies, 0.01, n);
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println!("{:.9f}", energy(&bodies) as float);
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}
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