inverse method

void inverse ()

Invert this.

Implementation 

void inverse() {
  final double l = 1.0 / length2;
  _qStorage[3] = _qStorage[3] * l;
  _qStorage[2] = -_qStorage[2] * l;
  _qStorage[1] = -_qStorage[1] * l;
  _qStorage[0] = -_qStorage[0] * l;
}