public Quaternion subtract(Quaternion q) {
        return new Quaternion(x - q.x, y - q.y, z - q.z, w - q.w);
    }
Subtracts the argument and returns difference as a new instance. The
current instance is unaffected.

@param q the quaternion to subtract (not null, unaffected)
@return a new Quaternion
jme3-core/src/main/java/com/jme3/math/Quaternion.java