//System.out.println("relativistic version on");
if (s.f instanceof CombinedForce) {
ArrayList<Force> forces = ((CombinedForce) s.f).forces;
for (int j = 0; j < forces.size(); j++) {
if (forces.get(j) instanceof ConstantForce){
forces.set(j, new ConstantForceRelativistic(s.getSpeedOfLight()));
}
if (forces.get(j) instanceof SimpleGridForce){
forces.set(j, new SimpleGridForceRelativistic(s));
}
}