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clear all;
clc;
hold on;

x = linspace(0, 2, 20);
y = linspace(0, 2, 20);

[X1, Y1] = meshgrid(x, y);

ax = X1;
ay = Y1;
az = sqrt((1 - X1.^(2) - Y1.^(2))/2);

surf(ax, ay, az);
axis ([0 2 0 2 0 4]);
xlabel('x');
ylabel('y');
zlabel('z');