boids_2D_simulation/functions.cpp at main · simop07/boids_2D_simulation · GitHub

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#include "functions.hpp"

double distance(Boid const &b1, Boid const &b2) {
  auto const pos_diff{b1.pos - b2.pos};
  return pos_diff.norm();
}

double distance(Boid const &b, Predator const &p) {
  auto const pos_diff{b.pos - p.pos};
  return pos_diff.norm();
}

Vector_2d calc_c_m_b_i(std::vector<Boid> const &flock, Boid const &b_i) {
  double const n = flock.size();

  // Asserts check if there are at least two boids in the flock, since it
  // wouldn't make sense to calculate the following functions with only one boid
  // present
  assert(n > 1);

  auto c_m_j = std::accumulate(flock.begin(), flock.end(), Vector_2d{},
                               [&](Vector_2d &c_m, Boid const &b_j) {
                                 c_m += (b_j.pos * (1 / (n - 1)));
                                 return c_m;
                               });

  return c_m_j - (b_i.pos * (1. / (n - 1.)));
}

double mean_distance(std::vector<Boid> const &flock) {
  double const n = flock.size();
  int i{};
  double sum_tot{};
  double sum_par{};

  assert(n > 1);

  std::for_each(flock.begin(), flock.end(), [&](Boid const &b_i) {
    auto nx = std::next((flock.begin() + i));
    sum_par = std::accumulate(nx, flock.end(), 0.,
                              [&](double sum_p, Boid const &b_j) {
                                sum_p += (distance(b_i, b_j));
                                return sum_p;
                              });

    sum_tot += sum_par;
    sum_par = 0.;
    ++i;
  });

  // Number of distances equals the combinations of n boid, taken at groups of
  // two
  double const c_n_2{(n * (n - 1.) / 2.)};
  double res = sum_tot / c_n_2;
  return res;
}

double std_dev_distance(std::vector<Boid> const &flock) {
  double const n = flock.size();
  double const mean_d = mean_distance(flock);
  int i{};
  double sum_tot{};
  double sum_d_i2{};

  assert(n > 1);

  std::for_each(flock.begin(), flock.end(), [&](Boid const &b_i) {
    auto nx = std::next((flock.begin() + i));
    sum_d_i2 = std::accumulate(
        nx, flock.end(), 0., [&](double sum_d, Boid const &b_j) {
          sum_d += ((distance(b_i, b_j)) * (distance(b_i, b_j)));
          return sum_d;
        });

    sum_tot += sum_d_i2;
    sum_d_i2 = 0.;
    ++i;
  });

  double const c_n_2{(n * (n - 1.) / 2.)};
  double res;
  if (n != 2) {
    res = sqrt((sum_tot / (c_n_2 - 1.)) - n * mean_d * mean_d / (n - 1));
  } else {
    res = NAN;
  }
  return res;
}

double mean_velocity(std::vector<Boid> const &flock) {
  double const n = flock.size();

  assert(n > 1);

  auto sum_v = std::accumulate(flock.begin(), flock.end(), 0.,
                               [](double sum_v, Boid const &b_j) {
                                 sum_v += (b_j.vel.norm());
                                 return sum_v;
                               });

  double res = sum_v * (1. / n);
  return res;
}

double std_dev_velocity(std::vector<Boid> const &flock) {
  double const n = flock.size();
  double sum_tot{};
  double mean_v = mean_velocity(flock);

  assert(n > 1);

  auto sum_v_i2 = std::accumulate(flock.begin(), flock.end(), 0.,
                                  [](double sum_v, Boid const &b_j) {
                                    sum_v += (b_j.vel.norm() * b_j.vel.norm());
                                    return sum_v;
                                  });

  sum_tot += sum_v_i2;
  double res = sqrt((sum_v_i2 / (n - 1.)) - n * mean_v * mean_v / (n - 1));
  return res;
}

Vector_2d sep(std::vector<Boid> const &flock, Boid const &b_i, double const s,
              double const d_s) {
  Vector_2d sum_v;

  std::for_each(flock.begin(), flock.end(), [&](Boid const &b_j) {
    if (distance(b_i, b_j) < d_s) {
      sum_v += (b_j.pos - b_i.pos);
    }
  });
  return -sum_v * s;
}

Vector_2d all(std::vector<Boid> const &flock, Boid const &b_i, double const a) {
  double const n = flock.size();

  assert(n > 1);

  auto sum_v = std::accumulate(flock.begin(), flock.end(), Vector_2d{},
                               [](Vector_2d sum_v, Boid const &b_j) {
                                 sum_v += b_j.vel;
                                 return sum_v;
                               });

  Vector_2d mean_v = (sum_v - b_i.vel) * (1. / (n - 1.));
  return (mean_v - b_i.vel) * a;
}

Vector_2d coe(Boid const &b_i, Vector_2d const &c_m, double const c) {
  return (c_m - b_i.pos) * c;
}

Vector_2d pacman(Vector_2d &pos, Stats const &s) {
  if (pos.xcomp() < s.l_b) {
    pos.setx(s.r_b - abs(pos.xcomp() - s.l_b));
  }
  if (pos.xcomp() > s.r_b) {
    pos.setx(s.l_b + abs(pos.xcomp() - s.r_b));
  }
  if (pos.ycomp() > s.u_b) {
    pos.sety(s.b_b + abs(pos.ycomp()) - s.u_b);
  }
  if (pos.ycomp() < s.b_b) {
    pos.sety(s.u_b - abs(pos.ycomp() - s.b_b));
  }
  return pos;
}

std::vector<Boid> influence(std::vector<Boid> const &flock, Boid const &b_i,
                            double const d) {
  std::vector<Boid> range;

  std::for_each(flock.begin(), flock.end(), [&](Boid const &b_j) {
    if (distance(b_i, b_j) < d) {
      range.push_back(b_j);
    }
  });
  return range;
}