clear all
clf

tx = ty = linspace (-2, 2, 21)';
[xx, yy] = meshgrid (tx, ty);
% tz = xx.^2 + yy.^2;
tz = xx.^2 + 4*yy.^3-12*yy-2;

surf(tx, ty, tz)
xlabel("x")
ylabel("y")
zlabel("f(x,y)")
hold on

% [x, y] = meshgrid (-2:0.2:2);
% h = quiver (x, y, 2*x, 2*y);
% set (h, "maxheadsize", 0.33);

% hold off
