plus-minus function surf graph

This all works fine when I just graph half of the equation Y (either the positive or negative side) but it gives me dimensions must agree error when I add Y=[Y -Y]. I'm not sure why. How do I plot the positive and negative results together?

clear
B=0.5;
L=4;
D=0.5;
x=linspace(-L/2,L/2,50);
z=linspace(-D,0,50);
[X,Z]=meshgrid(x,z);

Y=B/2*(1-(4*X.^2)./L^2)*(1-Z.^2./D^2);
Y=[Y -Y];
figure; surf(X,Y,Z)

Answer 1

[Honglei Chen]

Hi Sean,

If you just want to plot, you should do

figure;
surf(X,Y,Z);
hold on;
surf(X,-Y,Z);

HTH

[Sean Smith]

thank you, HUGE help.