void apply_border_forces(scalar_t dt, scalar_t xmin, scalar_t ymin, scalar_t xmax, scalar_t ymax);
void apply_collision_forces(scalar_t dt, int n_polygon, Polygon *p);
void apply_border_forces(scalar_t dt, scalar_t xmin, scalar_t ymin, scalar_t xmax, scalar_t ymax);
void apply_collision_forces(scalar_t dt, int n_polygon, Polygon *p);