You can plot them separately using the following code
x = -5:0.1:5;
y = -5:0.1:5;
z = -5:0.1:5;
[X, Y] = meshgrid(x, y);
Z = 3*sqrt(1-X.^2/9-Y.^2/16);
Z(imag(Z)~=0) = inf;
surf(X, Y, Z);
[X, Z] = meshgrid(x, z);
Y = 5*ones(size(X));
figure;
surf(X, Y, Z);
[X, Y] = meshgrid(x, y);
Z = sqrt(9-Y.^2);
Z(imag(Z)~=0) = inf;
figure;
surf(X, Y, Z);
Or you can plot them together using this code
x = -5:0.1:5;
y = -5:0.1:5;
z = -3:0.1:3;
[X, Y] = meshgrid(x, y);
Z = 3*sqrt(1-X.^2/9-Y.^2/16);
Z(imag(Z)~=0) = inf;
surf(X, Y, Z);
hold on
[X, Z] = meshgrid(x, z);
Y = 5*ones(size(X));
% figure;
surf(X, Y, Z);
[X, Y] = meshgrid(x, y);
Z = sqrt(9-Y.^2);
Z(imag(Z)~=0) = inf;
% figure;
surf(X, Y, Z);
