public Coordinate2D( 
   double x,
   double y
)

{
  Coordinate2D v = new Coordinate2D(0, 1);
  // v.Magnitude = 1

  Coordinate2D other = new Coordinate2D(-1, 0);
  double dotProduct = v.DotProduct(other);
  // dotProduct = 0

  Coordinate2D w = v + other;
  // w = (-1, 1)

  w += other;
  // w = (-2, 1)

  w -= other;
  // w = (-1, 1)

  w = v;
  w.Rotate(Math.PI, other);
  // w = (-2, -1)

  w = other;

  w.Scale(-4);
  // w = (4, 0)
  // w.Magnitude = 4

  w.Move(-1, 4);
  // w = (3, 4)
  // w.Magnitude = 5

  w.Move(-6, -1);
  Tuple<double, double> components = w.QueryComponents();
  // components = (-3, 3)
  // w.Magnitude = 3 * Math.Sqrt(2)

  Coordinate2D unitVector = w.GetUnitVector();
  // w = (-Math.Sqrt(2) / 2, Math.Sqrt(2) / 2)
  // w.Magnitude = 1
  w.SetComponents(3, 4);
}

{
  List<Coordinate2D> outerCoordinates = new List<Coordinate2D>();
  outerCoordinates.Add(new Coordinate2D(10.0, 10.0));
  outerCoordinates.Add(new Coordinate2D(10.0, 20.0));
  outerCoordinates.Add(new Coordinate2D(20.0, 20.0));
  outerCoordinates.Add(new Coordinate2D(20.0, 10.0));

  // define the inner polygon as anti-clockwise
  List<Coordinate2D> innerCoordinates = new List<Coordinate2D>();
  innerCoordinates.Add(new Coordinate2D(13.0, 13.0));
  innerCoordinates.Add(new Coordinate2D(17.0, 13.0));
  innerCoordinates.Add(new Coordinate2D(17.0, 17.0));
  innerCoordinates.Add(new Coordinate2D(13.0, 17.0));

  PolygonBuilderEx pbEx = new PolygonBuilderEx(outerCoordinates);
  Polygon donutEx = pbEx.ToGeometry() as Polygon;
  double areaEx = donutEx.Area;       // area = 100

  pbEx.AddPart(innerCoordinates);
  donutEx = pbEx.ToGeometry() as Polygon;

  areaEx = donutEx.Area;    // area = 84.0

  areaEx = GeometryEngine.Instance.Area(donutEx);    // area = 84.0
}