There is always the definite possibility of a bug in ECJ: for example,  
I just routed out a long-standing one in Lawnmower recently (check  
CVS).  But another reason may be that Koza-I and Koza-II'ss results  
have proven historically difficult to reproduce.  There are a number  
of reasons for this, but here are two: the random number generator  
used in Koza-I and Koza-II was troublingly non-random; and certain  
variables are not as you'd expect in print.  For example, though Koza- 
I says 400 timesteps for Artificial Ant, in fact it's believed he used  
600.  So much subsequenty work used 400 timesteps as a result that  
that's the default for both ECJ and lil-gp.  You an change it to 600  
and see what's up.  There are other explanations for differences which  
have been offered which I don't want to get into here.

So: if we can nail down a bug, I'd love to find out.  But be prepared  
for the probability that it's Koza-I and not ECJ. One way to check for  
the possibility of an ECJ bug in certain problems is to run lil-gp and  
see which one it more or less agrees with.  Let me know what you get.

Sean

On Oct 27, 2009, at 5:37 PM, David F. Barrero wrote:

> Dear all,
>
> I am trying to reproduce Koza's performance curves for some typical GP
> problems implemented in ECJ, but I had a limited success. Some  
> problems
> such as simple regression have similar performance curves compared  
> with
> the ones shown in Koza I, while others (for instance, Santa Fe trail  
> or
> even 5 parity with ADFs) yields very different curves.
>
> In theory, should ECJ examples generate the same performance curves  
> than
> those shown in Koza I/II?.
>
>
> Thanks in advance,
>
> David
>
>
>
>
> -- 
> David F. Barrero
> Departamento de Automática
> Universidad de Alcalá
>
> Tlf: (34) 91-885-69-20
> Web : http://atc1.aut.uah.es/~david/
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> Skype: dfbarrero
>
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> -- 
>