grid on
    figure(1)
    hold on
    x = s:pas:f;
    n = length(x);
    for i=1:n
        y1(i) = functie(x(i));
        y2(i) = Neville(a1, b1, x(i));
    endfor
    axis([0 5 0 1])
    plot(x, y1, '*r');
    plot(x, y2, '*g');