# How to plot an implicit and dicontinues function?

1 view (last 30 days)
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

Alan Stevens on 24 Oct 2020
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 on 24 Oct 2020
Exactly.Thank you very much.

Alan Stevens on 24 Oct 2020
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 on 24 Oct 2020
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.

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