gyogun

main.cpp

#include <iostream>
#include <array>
#include <numbers>
#include <cmath>

int const N = 10;
int prev(int n) {
    return (N + n - 1) % N;
}
double const dt = 0.0001;
double const to = 100;
int const max_step = to / dt + 1;
double const K = 1;
int const by = max_step / 5000;

int main(int, char**) {
  std::array<std::pair<double, double>, N> xs, vs;
  for (int i{}; i < size(xs); ++i) {
    using std::numbers::pi;
    auto arg = 2 * pi / N * i;
    xs[i] = std::make_pair(std::cos(arg), std::sin(arg));
  }

  for (int i{}; i < max_step; ++i) {
    for (int j{}; j < size(xs); ++j) {
      // symplectic
      xs[j].first  += vs[j].first  * dt;
      xs[j].second += vs[j].second * dt;
      vs[j].first  = K * (xs[prev(j)].first - xs[j].first);
      vs[j].second = K * (xs[prev(j)].second - xs[j].second);
    }
    if(i / by * by == i) {
      for(int j{}; j < size(xs); ++j) {
        std::cout << dt * i << ' ' << j << ' ' << xs[j].first << ' ' << xs[j].second << ' ' << vs[j].first << ' ' << vs[j].second << std::endl;
      }
      std::cout << std::endl;
    }
  }

  return 0;
}

orbit.png

plot.sh

#! /bin/bash

cat << EOS | gnuplot
set terminal png
set out 'orbit.png'
p 'out.dat' u 3:4 w p
EOS