function err = dfcent(x0,h)

% formule de differences finies
diff = (f(x0 + 2 * h) - 2 * f(x0 + h) + f(x0)) / (h * h);
err = abs(diff - df(x0));
fprintf(' h %e erreur %e \n',h,err)
end

% la fonction f
function funct = f(x)
funct = ???;
end
% la derivee seconde de f
function dfunct = df(x)
dfunct = ???;
end
