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Sean Luke  

Please remove me from email as I am not using your system.  
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---------- Original message ----------------------
From: Sean Luke <[log in to unmask]>
> On Jul 27, 2007, at 2:28 PM, Peter Walker wrote:
> 
> > 1)       (Traditional mutation): select a random node and remove it  
> > (along with all its children) and replace it by a randomly  
> > generated subtree and subtree root.
> 
> This is ec.gp.koza.Mutation
> 
> > The other two schemes I would like to implement are based on “point- 
> > mutation”. Both point-mutation schemes would start out by selecting  
> > a node and generate a random node (e.g. symbol1) to replace it.  
> > Symbol1 would be checked to see whether it is of the same arity as  
> > the node. If it is, then the node would be replaced by symbol1. If  
> > they are not of the same arity, then we would either:
> >
> > 2)      Pick another symbol until we find one of the same arity; OR
> >
> > 3)      Remove the node and replace it with a new subtree using  
> > symbol1 as the root.
> 
> You'll need to make a custom mutator for this that FIRST picks a  
> replacement and THEN decides on what to do (#2 or #3).  However:
> 
> - ec.gp.breed.MutateOneNodePipeline will pick another node guaranteed  
> to be of the same arity (and type equivalence) and replace the node  
> with the new node.  This is roughly equivalent to #2, as you've noted.
> 
> - #1 and #3 are roughly equivalent, it'd seem.
> 
> So I think you'll be writing a custom mutator -- take a look at the  
> code of these classes to get an idea about how to go about doing this  
> (it's nontrivial but doable!)
> 
> Sean