fillText(i, client_x_center + 5, client_y_center - i*client_y_step + 16);
    }
    context.strokeStyle="#000000";
    context.stroke();
    context.closePath();
}

// polynomial
var polynomial_xs = [1.0, 4.0, 7.0];
var polynomial_ys = [5.0, 2.0, 5.0];
var polynomial_n = 3;
var polynomial_i = 0;

function init_polynomial(){
    polynomial = document.getElementById("polynomial");
    var canvas_rect = polynomial.getBoundingClientRect();
    polynomial_draw(0, 0, false);

    polynomial.addEventListener('mous