Dear Fabio,

This may be of help with your problem, and as the Proff says AppendTo is very slow above a few thousand deep, I use the following Commands, Sow and Reap, the little snippet of code shows an example of its use.

Timing[vv = Reap[Do[Sow[{n, 2 n, 3 n}], {n, 1, 2000000}]]; 
 vv = Flatten[vv[[2]], 1]; Length[vv]]

{2.418016, 2000000}

Extracting the second part of the list removes the null statement part and flattening it reduces the 2 deep list to 1. Maybe this could be implemented in your code.

Paul.

Dear Fabio, my experience (also the advice of experienced collegues) is that AppendTo is a performance-killer. If ever possible find the required array length first (probably a bit too large if only an upper bound for this length can be found) and then fill in the quantities which you allways append. The problem with appending is that it typically involves re-allocation of the array. Unfortunately I'm in a hurry and not able to work out whether this advice acan be followed in your case.