ec.gp.push

Class Nonterminal

java.lang.Object

ec.gp.GPNode

ec.gp.push.Nonterminal

All Implemented Interfaces:

GPNodeParent, Prototype, Setup, Serializable, Cloneable

public class Nonterminal
extends GPNode

ECJ implements Push's s-expressions as trees of nonterminals and terminals. The nonterminals are all dummies -- this is the class in question. Notably the nonterminals also have an arbitrary arity, requiring a custom tree builder (see PushBuilder). The terminals are instances of Terminal.java.

See Also:

Serialized Form

Field Summary

Fields inherited from class ec.gp.GPNode

argposition, children, CHILDREN_UNKNOWN, constraints, GPNODEPRINTTAB, MAXPRINTBYTES, NODESEARCH_ALL, NODESEARCH_NONTERMINALS, NODESEARCH_TERMINALS, P_NODE, P_NODECONSTRAINTS, parent

Constructor Summary

Constructors

Constructor and Description
Nonterminal()

Method Summary

Methods

Modifier and Type	Method and Description
void	eval(EvolutionState state, int thread, GPData input, ADFStack stack, GPIndividual individual, Problem problem) Evaluates the node with the given thread, state, individual, problem, and stack.
String	toString() Returns a Lisp-like atom for the node which can be read in again by computer.
String	toStringForHumans() Returns a Lisp-like atom for the node which is intended for human consumption, and not to be read in again.

Methods inherited from class ec.gp.GPNode

atDepth, checkConstraints, clone, cloneReplacing, cloneReplacing, cloneReplacing, cloneReplacingAtomic, cloneReplacingAtomic, cloneReplacingNoSubclone, constraints, contains, defaultBase, depth, errorInfo, expectedChildren, iterator, iterator, iterator, lightClone, makeCTree, makeGraphvizSubtree, makeGraphvizTree, makeLatexTree, makeLispTree, makeLispTree, name, nodeEquals, nodeEquivalentTo, nodeHashCode, nodeInPosition, nodeInPosition, numNodes, numNodes, parentType, pathLength, printNode, printNode, printNode, printNodeForHumans, printNodeForHumans, printRootedTree, printRootedTree, printRootedTree, printRootedTreeForHumans, printRootedTreeForHumans, readNode, readNode, readRootedTree, readRootedTree, replaceWith, resetNode, rootedTreeEquals, rootedTreeHashCode, rootParent, setup, swapCompatibleWith, toStringForError, writeNode, writeRootedTree

Methods inherited from class java.lang.Object

equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

Nonterminal

public Nonterminal()

Method Detail

toString

public String toString()

Description copied from class: GPNode

Returns a Lisp-like atom for the node which can be read in again by computer. If you need to encode an integer or a float or whatever for some reason (perhaps if it's an ERC), you should use the ec.util.Code library.

Specified by:

toString in class GPNode

toStringForHumans

public String toStringForHumans()

Description copied from class: GPNode

Returns a Lisp-like atom for the node which is intended for human consumption, and not to be read in again. The default version just calls toString().

Overrides:

toStringForHumans in class GPNode

eval

public void eval(EvolutionState state,
        int thread,
        GPData input,
        ADFStack stack,
        GPIndividual individual,
        Problem problem)

Description copied from class: GPNode

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;
    }
        

Specified by:

eval in class GPNode