function I = adquad(f, a, b, err, m)
  I1 = trapz_int(f, a, b, m);
  I2 = trapz_int(f, a, b, 2*m);
  if abs(I1 - I2) < err % success
    I = I2;
    return
  else % recursive subdivision
    I = adquad(f, a, (a+b)/2, err, m) + adquad(f, (a+b)/2, b, err, m);
  end
end;