find horizontal tangent plane postitions for this surface in a -20 - +20 cube space: in matlab

main.m
% Define the surface function
f = @(x, y) x^2 + y^3;

% Define the gradient of the function
syms x y
gradF = [diff(f(x, y), x), diff(f(x, y), y)];

% Define the x, y values in the cube space
x_values = -20:1:20;
y_values = -20:1:20;

% Find the points where the gradient is [0, 0]
tangent_plane_positions = [];
for i = 1:length(x_values)
    for j = 1:length(y_values)
        grad = double(subs(gradF, [x, y], [x_values(i), y_values(j)]));
        if isequal(grad, [0, 0])
            tangent_plane_positions = [tangent_plane_positions; x_values(i), y_values(j)];
        end
    end
end

disp(tangent_plane_positions);
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