< min_d){
                min_d = di;
                min_i = i;
            }
        }
        runge_i = min_i;
        runge_context.setLineDash([4, 4]);
        runge_context.beginPath();
        runge_context.moveTo(x_to_client(runge_xs[min_i]), y_to_client(runge_ys[min_i]));
        runge_context.lineTo(client_x, client_y);
        runge_context.strokeStyle="#AA3311";
        runge_context.stroke();
        runge_context.closePath();
        runge_context.setLineDash([]);
    }
}


//  Chebyshev
funct