How to plot an implicit and dicontinues function?

Hello, I want to ask how to plot the level curves of this function. I have tried with fimplicit and with fcontour but I can't plot it because of its discontinuities. If anyone knows it will be very helpful because it is for my composite structures course.

function [z] = THb(x1,x2)
E1 = 100*10^3;E2 = 7*10^3;nu12=.3;F1t=1000;F2t=45;F1c=600;F2c=150;F6=65;
    if x1>=0
        A=1/F1t^2;
        C=-(1/F1t^2);
    else
        A=1/F1c^2;
        C=-(1/F1c^2);
    end
    if x2>=0
        B=1/F2t^2;
    else
        B=1/F2c^2;
    end

z=A*x1.^2 + B*x2.^2 +C*x1.*x2;

end

Answer 1

[Alan Stevens]

Do you mean like this (type doc contour for more detail):

x1 = -2:0.01:2;  
x2 = -2:0.01:2;
[x, y] = meshgrid(x1, x2);
z = THb(x,y);
lvls = [1 2 5 10 15 20 40 60]*10^-6;  % Set the contour values you want to see
contour(x,y,z,lvls,'ShowText','on')
xlabel('x1'),ylabel('x2'),zlabel('z')

... etc.

[Francisco Patitucci Perez]

Exactly.Thank you very much.

Answer 2

[Alan Stevens]

Something like the following? (You could use surfc if you want contours as well):

x1 = -10:10;  
x2 = -10:10;
[x, y] = meshgrid(x1, x2);
z = THb(x,y);
surf(x,y,z)
xlabel('x1'),ylabel('x2'),zlabel('z')

function [z] = THb(x1,x2)
E1 = 100*10^3;E2 = 7*10^3;nu12=.3;F1t=1000;F2t=45;F1c=600;F2c=150;F6=65;
    if x1>=0
        A=1/F1t^2;
        C=-(1/F1t^2);
    else
        A=1/F1c^2;
        C=-(1/F1c^2);
    end
    if x2>=0
        B=1/F2t^2;
    else
        B=1/F2c^2;
    end

z=A*x1.^2 + B*x2.^2 +C*x1.*x2;

end

[Francisco Patitucci Perez]

This plots me the surface or the level curves for different values of z, but I want to be able to specify which level curve I want to plot because I need the curves for specific values of z.