Partial Differentiation - Saddle Point I
Visualising gradient of z = f(x,y) in either the x direction or the y direction
The equation for z = f(x,y) is:
At the critical point, the curvature in the x direction is increasing (concave up), and the curvature in the y direction is decreasing (concave down).
In addition, , and so the critical point is a saddle point.