double f = force_multiplier * (desiredLen - len) / len;
// f = f * Math.pow(stretch, (v1.degree() + v2.degree() - 2));
// shuwu: reduced the degree attenuation with a sqrt dampener
f = f * Math.pow(stretch, Math.sqrt((v1.degree() + v2.degree() - 2)));
// the actual movement distance 'dx' is the force multiplied by
// the
// distance to go.
double dx = f * vx;