Hierarchical Gene Expression Programming (HGEP)

I've been meaning to write this idea down for a while, because it is potentially interesting, and if nothing else it is yet another variation on GEP- of which there are already so many.
While it is nice that GEP is so flexible to allow many possible changes, many of them are either very complex, IGEP, or lost generality, NGEP. On the other hand, some remove complexity, like PGEP-which I think all GEP researchers should be using instead of GEP- or increase complexity in a very reasonable way, like BGEP. I'm hoping that HGEP is a reasonable increase in complexity, and I think of it as having potential benefits in domain specific ways, unlike PGEP which seems pretty generally to be an advantage over GEP.


So- HGEP. Or more like HPGEP, as I prefer prefix notation over karva. It is a sort of synthesis between the multi-genetic chromosomes of GEP(with a single linking function) and the single gene chromosomes of PGEP. It exploits the homomorphism between the fact that terminals are linked by operators, and that genes can be linked by operators. So why have only one linking function? Why not have each gene be a "terminal" in a second order GEP, where the operators are the same, but each terminal is an entire gene? While each HGEP individual would have an equivalent GEP individual, the GEP one would be very long and easy to disrupt. HGEP would impose the idea of hierarchy on the individual, and allow genes to combine in interesting ways, rather than guessing which linking function might be useful and imposing it over all genes.
This may introduce to much complexity to the individuals, especially because they would have variable numbers of genes. To fix the number of genes we could just have a GA style list of operators included in the front of the chromosome, and use it to link the genes. This would allow variation in linking functions without imposing so much complexity.


I will probably flesh this idea out a little more in another post. It is not so well developed at the moment.