public void ComputeBC(Node2 D, Node2 E, Node2 F)
{
double ox = default(double);
double oy = default(double);
Circle2.Circle3Pt(D.x, D.y, E.x, E.y, F.x, F.y, ref ox, ref oy, ref radius_squared);
center = new Node2(ox, oy);
radius = Math.Sqrt(radius_squared);
}