4425.sagews

var('x y')
f(x,y) = x^(2)-x*y
plot3d(f(x,y), (x, -3 ,3), (y, -3, 3));

plot_vector_field(f.gradient(), (x, -3, 3), (y, -3, 3), aspect_ratio=1) + contour_plot(f(x,y), (x, -3, 3), (y, -3, 3), fill=True, contours=15)

g(x, y) = exp(-(x^2+sin(y^2))/4)
plot3d(g(x,y), (x, -3 ,3), (y, -3, 3))

plot_vector_field(g.gradient(), (x, -3, 3), (y, -3, 3), aspect_ratio=1) + contour_plot(g(x,y), (x, -3, 3), (y, -3, 3), fill=True, contours=15)