/**
  * checks if vector is Collinear to given vector
  *
  * @return true if vectors are Collinear else false
  */
 public boolean isCollinearTo(Vector3D V) {
   if (Math.abs(this.DotProduct(V)) == this.getLength() * V.getLength()) {
     return true;
   } else {
     return false;
   }
 }
 /**
  * checks if vector is parallel to given vector
  *
  * @return true if vectors are parallel else false
  */
 public boolean isParallel_to(Vector3D V) {
   if (this.DotProduct(V) == this.getLength() * V.getLength()) {
     return true;
   } else {
     return false;
   }
 }