hold off;

n=5;


% Plot the original function
xi=-5:0.01:5;
yi=1./(1+xi.*xi);
hold off;
plot(xi,yi,'b');
hold on;


%Lagrange poly with n  (equally spaced) nodes

x=-5:10/n:5;
y=1./(1+x.*x)
a=polyfit(x,y,n);
yi=polyval(a,xi);
plot(xi,yi,'r')


%compute the error at q

q=1+sqrt(10)
trueval=1/(1+q^2)
compval=polyval(a,q)
error=abs(trueval-compval)