mirror of https://github.com/exaloop/codon.git
154 lines
4.7 KiB
C++
154 lines
4.7 KiB
C++
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#include <chrono>
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#include <cmath>
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#include <iostream>
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#include <string>
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#include <unordered_map>
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#include <utility>
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#include <vector>
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namespace {
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const double PI = 3.14159265358979323;
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const double SOLAR_MASS = 4 * PI * PI;
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const double DAYS_PER_YEAR = 365.24;
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struct Body {
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std::vector<double> r, v;
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double m;
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};
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std::unordered_map<std::string, Body> BODIES = {
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{"sun", {{0.0, 0.0, 0.0}, {0.0, 0.0, 0.0}, SOLAR_MASS}},
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{"jupiter",
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{{4.84143144246472090e+00, -1.16032004402742839e+00, -1.03622044471123109e-01},
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{1.66007664274403694e-03 * DAYS_PER_YEAR, 7.69901118419740425e-03 * DAYS_PER_YEAR,
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-6.90460016972063023e-05 * DAYS_PER_YEAR},
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9.54791938424326609e-04 * SOLAR_MASS}},
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{"saturn",
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{{8.34336671824457987e+00, 4.12479856412430479e+00, -4.03523417114321381e-01},
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{-2.76742510726862411e-03 * DAYS_PER_YEAR,
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4.99852801234917238e-03 * DAYS_PER_YEAR,
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2.30417297573763929e-05 * DAYS_PER_YEAR},
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2.85885980666130812e-04 * SOLAR_MASS}},
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{"uranus",
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{{1.28943695621391310e+01, -1.51111514016986312e+01, -2.23307578892655734e-01},
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{2.96460137564761618e-03 * DAYS_PER_YEAR, 2.37847173959480950e-03 * DAYS_PER_YEAR,
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-2.96589568540237556e-05 * DAYS_PER_YEAR},
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4.36624404335156298e-05 * SOLAR_MASS}},
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{"neptune",
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{{1.53796971148509165e+01, -2.59193146099879641e+01, 1.79258772950371181e-01},
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{2.68067772490389322e-03 * DAYS_PER_YEAR, 1.62824170038242295e-03 * DAYS_PER_YEAR,
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-9.51592254519715870e-05 * DAYS_PER_YEAR},
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5.15138902046611451e-05 * SOLAR_MASS}},
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};
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template <typename K, typename V> auto values(std::unordered_map<K, V> &m) {
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std::vector<V *> v;
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v.reserve(m.size());
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for (auto &e : m)
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v.push_back(&e.second);
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return v;
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}
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template <typename T> auto combinations(const std::vector<T> &v) {
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std::vector<std::pair<T, T>> p;
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auto n = v.size();
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p.reserve(n);
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for (auto i = 0; i < n - 1; i++)
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for (auto j = i + 1; j < n; j++)
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p.push_back({v[i], v[j]});
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return p;
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}
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std::vector<Body *> SYSTEM = values(BODIES);
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auto PAIRS = combinations(SYSTEM);
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void advance(double dt, int n, std::vector<Body *> &bodies = SYSTEM,
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std::vector<std::pair<Body *, Body *>> &pairs = PAIRS) {
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for (int i = 0; i < n; i++) {
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for (auto &pair : pairs) {
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double x1 = pair.first->r[0], y1 = pair.first->r[1], z1 = pair.first->r[2];
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auto &v1 = pair.first->v;
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double m1 = pair.first->m;
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double x2 = pair.second->r[0], y2 = pair.second->r[1], z2 = pair.second->r[2];
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auto &v2 = pair.second->v;
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double m2 = pair.second->m;
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double dx = x1 - x2, dy = y1 - y2, dz = z1 - z2;
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double mag = dt * std::pow((dx * dx + dy * dy + dz * dz), -1.5);
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double b1m = m1 * mag;
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double b2m = m2 * mag;
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v1[0] -= dx * b2m;
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v1[1] -= dy * b2m;
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v1[2] -= dz * b2m;
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v2[0] += dx * b1m;
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v2[1] += dy * b1m;
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v2[2] += dz * b1m;
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}
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for (auto *body : bodies) {
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auto &r = body->r;
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double vx = body->v[0], vy = body->v[1], vz = body->v[2];
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r[0] += dt * vx;
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r[1] += dt * vy;
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r[2] += dt * vz;
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}
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}
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}
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void report_energy(std::vector<Body *> &bodies = SYSTEM,
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std::vector<std::pair<Body *, Body *>> &pairs = PAIRS,
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double e = 0.0) {
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for (auto &pair : pairs) {
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double x1 = pair.first->r[0], y1 = pair.first->r[1], z1 = pair.first->r[2];
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auto &v1 = pair.first->v;
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double m1 = pair.first->m;
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double x2 = pair.second->r[0], y2 = pair.second->r[1], z2 = pair.second->r[2];
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auto &v2 = pair.second->v;
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double m2 = pair.second->m;
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double dx = x1 - x2, dy = y1 - y2, dz = z1 - z2;
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e -= (m1 * m2) / std::pow((dx * dx + dy * dy + dz * dz), 0.5);
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}
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for (auto *body : bodies) {
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double vx = body->v[0], vy = body->v[1], vz = body->v[2];
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double m = body->m;
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e += m * (vx * vx + vy * vy + vz * vz) / 2.;
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}
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std::cout << e << std::endl;
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}
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void offset_momentum(Body &ref, std::vector<Body *> &bodies = SYSTEM, double px = 0.0,
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double py = 0.0, double pz = 0.0) {
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for (auto *body : bodies) {
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double vx = body->v[0], vy = body->v[1], vz = body->v[2];
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double m = body->m;
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px -= vx * m;
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py -= vy * m;
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pz -= vz * m;
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}
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auto &v = ref.v;
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double m = ref.m;
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v[0] = px / m;
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v[1] = py / m;
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v[2] = pz / m;
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}
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} // namespace
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int main(int argc, char *argv[]) {
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using clock = std::chrono::high_resolution_clock;
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using std::chrono::duration_cast;
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using std::chrono::milliseconds;
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auto t = clock::now();
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std::string ref = "sun";
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offset_momentum(BODIES[ref]);
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report_energy();
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advance(0.01, std::atoi(argv[1]));
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report_energy();
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std::cout << (duration_cast<milliseconds>(clock::now() - t).count() / 1e3)
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<< std::endl;
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}
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