/// <summary>
/// A method to multiply a vector by 2.
/// </summary>
/// <param name="v">A vector.</param>
/// <returns>The multiplication of v by 2: (2*x, 2*y)</returns>
public IVector2D <T> Mul2(IVector2D <T> v)
{
return(new Vector2D <T>(Math.Mul2(v.X),
Math.Mul2(v.Y)));
}