public Vector3f getNegativeEnd(Vector3f store) {
        if (store == null) {
            store = new Vector3f();
        }
        return origin.subtract((direction.mult(extent, store)), store);
    }
Determine the location of this segment's negative end.

@param store storage for the result (modified if not null)
@return a location vector (either store or a new vector)
jme3-core/src/main/java/com/jme3/math/LineSegment.java