r=linspace(-1,1,100);
s=linspace(-1,1,100);
[x1,x2]=meshgrid(r,s);
z=1-x1.^2-x2.^2;
mesh(x1,x2,z)              % Plotter funksjonen
hold('on')
mesh(x1,x2,ones(size(z)))  % Plotter tangentplanet