XX = linspace(-2,2,500);  YY = 1./(1+25*XX.^2);
plot(XX,YY);
X = linspace(-2,2,11);  Y = 1./(1+25*X.^2);
[P,R,S] = lagrangepoly(X,Y);
xx = -2:.01:2;

plot(xx,polyval(P,xx),X,Y,'or');
grid;