function cubic_spline
f = @(x) 1./(1+x.^2);
a = linspace(-5,5,1000);
b = f(a);
error=[];
for n = 2.^(1:15)
x = linspace(-5,5,n);
y = f(x);
c = spline(x,y,a);
error=[error,max(abs(b-c))];
end
loglog(2.^(1:15),error)
grid on