h=1; x=pi/4; k=1;

while h>1e-17
  [et1,et2,et3] = deri(x,h);
  e1(k) = et1; e2(k) = et2; e3(k) = et3; h1(k)=h;
  k = k+1;
  h = h/2;
end

loglog(h1,e1);
figure(2); loglog(h1,e2)
figure(3); loglog(h1,e3);