 synthesis_context.stroke();
        synthesis_context.closePath();
        synthesis_context.setLineDash([]);
    }
}


// Runge
var runge_xs = [-1.0, 0.0, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0];
var runge_ys = [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 5.0, 4.0, 3.0, 2.0, 1.0];
var runge_n = 11;
var runge_i = 0;

function init_runge(){
    runge = document.getElementById("runge");
    var canvas_rect = runge.getBoundingClientRect();
    runge_draw(0, 0, false);

    runge.addEventListener('mousemove', function