This simulation shows the geometric interpretation of the directional derivative of [i]f[/i] in the direction of a unit vector [b]u[/b] and the gradient vector of [i]f[/i]([i]x[/i],[i]y[/i]) at the point P∈[math]\mathbb{R}^2[/math].[br]Things to try:[br][list][*]Change the function f(x,y).[/*][*]Drag the point P or type specific values on the boxes.[/*][*]Activate box [b]Dir. derivative[/b] to show the directional derivative. Change the angle θ by dragging the slider or type an specific value on the box.[/*][*]Use right click and drag the mouse to rotate the 3D view or click on [b]View[/b] button.[/*][/list][br][b]Note:[/b] The blue arrow represents the gradient vector at P.