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If I do this, I will implement a check() method for the Individual class
you are using. (Assuming you have one tree for every individual) In this
check method, I traverse through the tree and keep track of occurances of
each kind of node. If the tree does not satisfy you condition. I will mark
it as "bad".
You can remove "bad" individuals from your population in many places. Maybe
pre-breed or post-breed.
Other means are also possible, you don't need to strictly follow this.

On Tue, Feb 25, 2014 at 1:43 AM, Francisco Lopez de la Franca <
[log in to unmask]> wrote:

> But, how do I do that? I mean, where do I check (in the code) that the
> individual generated does not fulfill the requirement of appearing every
> node at least once?
> Thanks a lot.
>
>
> 2014-02-24 19:56 GMT+01:00 Xiaomeng Ye <[log in to unmask]>:
>
> Or you can simply discard any non-conformed individuals, during any
>> process (initialization, breeding). And keep generating new individuals
>> until your population is filled with the individuals conforming to this
>> rule.
>>
>>
>> On Mon, Feb 24, 2014 at 1:13 PM, Sean Luke <[log in to unmask]> wrote:
>>
>>> Francisco, ECJ can't do this by default: and I really have no idea how
>>> to require this constraint.  You'll have to either enforce this rule in the
>>> tree builder algorithm and/or the crossover mutation operators.
>>>  Alternatively you can assess the fitness of non-confirming individuals as
>>> very low.
>>>
>>> Sean
>>>
>>> On Feb 24, 2014, at 6:57 AM, Francisco Lopez de la Franca <
>>> [log in to unmask]> wrote:
>>>
>>> > Hello.
>>> >
>>> > I am new in ECJ. I'm going to use ECJ to find the solution of a second
>>> degree equation, that is, x=(-b+sqrt(b^2-4ac))/(2a).
>>> > I've implemented as FunctionSet the following nodes: add, sub, sqrt,
>>> square, mul, div, neg, a, b, c, 2 and 4.
>>> > I've followed the instructions described both in the tutorial4 in the
>>> documentations provided with ECJ and the one in the ECJ manual.
>>> >
>>> > What I need and donot find the way, is to force to appear in the
>>> result tree the nodes: a, b, c, 2, 4, -, +, sqrt, square, div and mul. That
>>> is, to specify in some manner that the nodes must appear at least once.
>>> Moreover, I'd like to know if it is possible to set that one node must
>>> appear a number of times in the solution.
>>> >
>>> > I hope to have explained well.
>>> >
>>> > Thank you very much in advance.
>>> >
>>> > Regards.
>>>
>>
>>
>