Saddle point example

saddle_point.m

v = -5:0.5:5;
[x, y] = meshgrid(v);
z = x .* exp(x.^2 - y.^2) + y.*exp(-x.^2 + y.^2);
[px, py] = gradient(z);
figure
surf(x, y, z)
figure
contour(x, y, z);
hold on
quiver(x, y, px, py);
hold off

v = -5:0.5:5;
[x, y] = meshgrid(v);
z = (x.^2 - y.^2);
[px, py] = gradient(z);
figure
surf(x, y, z);
% hold on
% quiver3(x, y, px, py);
% hold off
figure
contour(x, y, z);
hold on 
quiver(x, y, px, py);
hold off