clf;
[X,Y] = meshgrid(-3:.1:3); 
%2x_1^3 + x_1 x_2^2 + 5 x_1^2 + x_2^2
Z = 2*X.^3 + X.*Y.^2 + 5*X.^2 + Y.^2;
surf(X,Y,Z)
colormap pink
hold on
a = 0; b = 0; 
c = 2*a^3 + a*b^2 + 5*a^2 + b^2;
plot3(a,b,c,'rs')

a = -5/3; b = 0; 
c = 2*a^3 + a*b^2 + 5*a^2 + b^2;
plot3(a,b,c,'bs')

a = -1; b = 2; 
c = 2*a^3 + a*b^2 + 5*a^2 + b^2;
plot3(a,b,c,'ys')

a = -1; b = -2; 
c = 2*a^3 + a*b^2 + 5*a^2 + b^2;
plot3(a,b,c,'ys')

%alpha(.4)
hold off
