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x = -5:0.01:5;
y = x.^2;
[X, Y] = cylinder(y)
surf(X,Y)
 

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shading interp

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val = 3;

[X, Y] = meshgrid(-val:0.01:val, -val:0.01:val);
Z = X.^2 + Y.^2;
surf(X, Y, Z);
shading interp

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Z(Z > val^2) = nan;

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[r,the]=meshgrid([0:0.1:5],[0:pi/10:2*pi]);
x=r.*cos(the);
y=r.*sin(the);
z=x.^2+y.^2;
surf(x,y,z);

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i = 3;
[r,t] = meshgrid([-i:0.1:i],[-1:0.1:i]);
x = r.* cos(t);
y = r.* sin(t);
z = x.^2 + y.^2;
z1 = -z +10;   % damit nach unten geöffnet und bei 0 beginnent
surf(x,y,z1)

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 x(1,10) = 0;
>> x(1,:) = 10;
>> y = x;
>> [X,Y] = meshgrid(x,y);
>> Z = X.^2 + Y.^2;
>> mesh(X,Y,Z)