c# compute best fit circle from many points

using System.Linq;
/// <summary>
/// Given a list of points, find a circle that roughly passes through them all.
/// </summary>
public static CircleSegment ComputeCircle(System.Collections.Generic.IEnumerable<Point2d> l)
{
    // https://www.scribd.com/document/14819165/Regressions-coniques-quadriques-circulaire-spherique
    // via http://math.stackexchange.com/questions/662634/find-the-approximate-center-of-a-circle-passing-through-more-than-three-points

    var n = l.Count();
    var sumx = l.Sum(p => p.X);
    var sumxx = l.Sum(p => p.X * p.X);
    var sumy = l.Sum(p => p.Y);
    var sumyy = l.Sum(p => p.Y * p.Y);

    var d11 = n * l.Sum(p => p.X * p.Y) - sumx * sumy;

    var d20 = n * sumxx - sumx * sumx;
    var d02 = n * sumyy - sumy * sumy;

    var d30 = n * l.Sum(p => p.X * p.X * p.X) - sumxx * sumx;
    var d03 = n * l.Sum(p => p.Y * p.Y * p.Y) - sumyy * sumy;

    var d21 = n * l.Sum(p => p.X * p.X * p.Y) - sumxx * sumy;
    var d12 = n * l.Sum(p => p.Y * p.Y * p.X) - sumyy * sumx;

    var x = ((d30 + d12) * d02 - (d03 + d21) * d11) / (2 * (d20 * d02 - d11 * d11));
    var y = ((d03 + d21) * d20 - (d30 + d12) * d11) / (2 * (d20 * d02 - d11 * d11));

    var c = (sumxx + sumyy - 2 * x * sumx - 2 * y * sumy) / n;
    var r = Math.Sqrt(c + x * x + y * y);

    return new CircleSegment(new Point2f((float)x, (float)y), (float)r);
}