To be consistent with literature, ECJ's default pipeline has  
probability of two-child crossover at 90% and probability of one- 
child reproduction at 10%.  No mutation pipelines are used.  If you  
wish to add one, you need to modify the pipeline parameters to  
include a mutator (there are plenty), for example, like this:

pop.subpop.0.species.pipe.num-sources = 3
pop.subpop.0.species.pipe.source.0 = ec.gp.koza.CrossoverPipeline
pop.subpop.0.species.pipe.source.0.prob = 0.7
pop.subpop.0.species.pipe.source.1 = ec.breed.ReproductionPipeline
pop.subpop.0.species.pipe.source.1.prob = 0.1
pop.subpop.0.species.pipe.source.2 = ec.gp.koza.MutationPipeline
pop.subpop.0.species.pipe.source.2.prob = 0.2

You may then need to modify parameters for your mutator (in this  
case, MutationPipeline) to mutate in the way you wish.

Sean

On Nov 23, 2006, at 10:38 AM, Serethos wrote:

> Perhaps I consequently overlooks it but I can not find the parameter
> entry for mutation probability in GP Problems. What is the default
> and where is it defined?