MATLAB: Help me plot 3D graph like these picture

Question

Answer 1

Try this

x = linspace(0,1,500);
y = linspace(0,1,500);
[Xg, Yg] = meshgrid(x, y);
mask = Yg > sqrt(Xg);
Zg = 1 - Yg;
Zg(~mask) = nan;
surf(Xg, Yg, Zg, 'FaceColor', 'b', 'FaceAlpha', 0.4, 'EdgeColor', 'none')
hold on
y = linspace(0,1,500);
z = linspace(0,1,500);
[Yg, Zg] = meshgrid(y, z);
mask = Yg < 1 - Zg;
Xg = Yg.^2;
Xg(~mask) = nan;
surf(Xg, Yg, Zg, 'FaceColor', 'b', 'FaceAlpha', 0.4, 'EdgeColor', 'none')
view(gca,[115 45]);