On Sun, 11 Sep 2011, Henrique Andrade wrote: OK, but could you please send mail in plain text? This is particularly important when trying to convey hansl code. I have edited what you posted to make the following intelligible. Welcome to digital computer arithmetic! Floating-point numbers are represented to finite precision (64 bits, generally, within gretl and most econometrics software). If you multiply x by z and then divide the product by z, you do not necessarily get exactly the original x as the answer. Your "constant" series is not constant so far as the computer is concerned: some values differ from the previous one by plus-or-minus a figure on the order of 10^{-14}. To see this, add above: <hansl> print z teste d_teste --byobs </hansl> Allin Cottrell