lient((b2 - db2 - a21*(x_max))/a22));
            context.moveTo(x_to_client(x_min), y_to_client((b2 + db2 - a21*(x_min))/a22));
            context.lineTo(x_to_client(x_max), y_to_client((b2 + db2 - a21*(x_max))/a22));
            context.strokeStyle="#6699ff";
            context.stroke();
            context.setLineDash([]);
            context.closePath();
        }
    }

    // iteration count
    results = document.getElementById("results");
    if(last_iterations > 100){
        results.innerHTML = 