Evaluates the node with the given thread, state, individual, problem, and stack.
Your random number generator will be state.random[thread].
The node should, as appropriate, evaluate child nodes with these same items
passed to eval(...).
About input: input is special; it is how data is passed between
parent and child nodes. If children "receive" data from their parent node when
it evaluates them, they should receive this data stored in input.
If (more likely) the parent "receives" results from its children, it should
pass them an input object, which they'll fill out, then it should
check this object for the returned value.
A tree is typically evaluated by dropping a GPData into the root. When the
root returns, the resultant input should hold the return value.
In general, you should not be creating new GPDatas.
If you think about it, in most conditions (excepting ADFs and ADMs) you
can use and reuse input for most communications purposes between
parents and children.
So, let's say that your GPNode function implements the boolean AND function,
and expects its children to return return boolean values (as it does itself).
You've implemented your GPData subclass to be, uh, BooleanData, which
looks like
public class BooleanData extends GPData
{
public boolean result;
public GPData copyTo(GPData gpd)
{
((BooleanData)gpd).result = result;
}
}
...so, you might implement your eval(...) function as follows:
public void eval(final EvolutionState state,
final int thread,
final GPData input,
final ADFStack stack,
final GPIndividual individual,
final Problem problem
{
BooleanData dat = (BooleanData)input;
boolean x;
// evaluate the first child
children[0].eval(state,thread,input,stack,individual,problem);
// store away its result
x = dat.result;
// evaluate the second child
children[1].eval(state,thread,input,stack,individual,problem);
// return (in input) the result of the two ANDed
dat.result = dat.result && x;
return;
}
- Overrides:
eval
in class ADF