This applet shows the surface defined by [math]f(x, y)[/math] along with the gradient vector [b][math]gradf[/math][/b] at the point [math]A=(x_0, y_0)[/math]. The point [math]A[/math] can be moved by dragging it or by using the sliders.[br][br]The vertical component of the vector [b][math]v[/math][/b] (on the tangent plane) is equal to the magnitude of the gradient.