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package jcgp.backend.population;
import java.util.ArrayList;
import jcgp.backend.function.Function;
import jcgp.backend.resources.Resources;
/**
* Nodes make up the main part of the chromosome,
* where the actual functions are evolved. Each node
* contains a function and a number of connections.
* The node outputs the result of performing its function
* on the values of its connections. Nodes therefore
* implement both {@code Mutable} and {@code Connection}
* since they can be mutated but also connected to.
* Nodes are constructed with a fixed number of connections
* (determined by the maximum arity of the function set)
* and must be reinstantiated if the experiment arity
* changes.
* <br><br>
* When mutating a node, it is easiest to use {@code mutate()}.
* Alternatively, you may also perform a specific mutation using
* {@code setConnection(...)} and {@code setFunction(...)}.
*
* @author Eduardo Pedroni
*
*/
public class Node implements Mutable, Connection {
private Function function;
private Connection[] connections;
private int column, row;
private Chromosome chromosome;
/**
* Constructs a new instance of {@code Node} with the
* specified parameters. Nodes must contain their
* own row and column for ease of copying.
*
* @param chromosome the chromosome this node belongs to.
* @param row the node's row.
* @param column the node's column.
*/
public Node(Chromosome chromosome, int row, int column) {
this.chromosome = chromosome;
this.column = column;
this.row = row;
}
/**
* Initialises the node with the specified values.
* The number of connections passed as argument must
* be exactly the same as the experiment arity, or
* an {@code IllegalArgumentException} will be thrown.
*
* @param newFunction the node function to set.
* @param newConnections the node connections to set.
*/
public void initialise(Function newFunction, Connection... newConnections) {
function = newFunction;
if (newConnections.length == chromosome.getResources().arity()) {
connections = newConnections;
} else {
throw new IllegalArgumentException("Received " + newConnections.length + " connections but needed exactly " + chromosome.getResources().arity());
}
}
/**
* @return this node's column.
*/
public int getColumn() {
return column;
}
/**
* @return this node's row.
*/
public int getRow() {
return row;
}
/**
* @return this node's function.
*/
public Function getFunction() {
return function;
}
/**
* Sets the node function.
*
* @param newFunction the new function to set.
*/
public void setFunction(Function newFunction) {
function = newFunction;
}
/**
* @param index the connection to return.
* @return the indexed connection.
*/
public Connection getConnection(int index) {
return connections[index];
}
/**
* This method sets the indexed connection to the specified new connection.
* If the given connection is null or disrespects levels back, it is discarded
* and no connections are changed.
*
* @param index the connection index to set.
* @param newConnection the {@code Connection} to connect to.
*/
public void setConnection(int index, Connection newConnection) {
// connection must not be null
if (newConnection != null) {
connections[index] = newConnection;
chromosome.recomputeActiveNodes();
}
}
/**
* For package use, this is a recursive method
* used to create a collection of active nodes
* in the chromosome. If this node is not already
* in the active node list, this method adds it.
* It then calls {@code getActive()} on each of its
* connections, therefore recursively adding every
* single active node to the given list.
*
* @param activeNodes the list of active nodes being built.
*/
protected void getActive(ArrayList<Node> activeNodes) {
// don't add the same node twice
if (!activeNodes.contains(this)) {
activeNodes.add(this);
}
// call getActive on all connections - they are all active
for (int i = 0; i < function.getArity(); i++) {
if (connections[i] instanceof Node) {
((Node) connections[i]).getActive(activeNodes);
}
}
}
@Override
public boolean copyOf(Mutable element) {
// both cannot be the same instance
if (this != element) {
// element must be instance of node
if (element instanceof Node) {
Node n = (Node) element;
// must have the same function
if (function == n.getFunction()) {
// row and column must be the same
if (column == n.getColumn() && row == n.getRow()) {
// connections must be the equivalent, but not the same instance
for (int i = 0; i < connections.length; i++) {
if (connections[i] != n.getConnection(i)) {
if (connections[i] instanceof Input && n.getConnection(i) instanceof Input) {
if (((Input) connections[i]).getIndex() != ((Input) n.getConnection(i)).getIndex()) {
return false;
}
} else if (connections[i] instanceof Node && n.getConnection(i) instanceof Node) {
if (((Node) connections[i]).getRow() != ((Node) n.getConnection(i)).getRow() &&
((Node) connections[i]).getColumn() != ((Node) n.getConnection(i)).getColumn()) {
return false;
}
} else {
return false;
}
} else {
return false;
}
}
// all connections checked, this really is a copy
return true;
}
}
}
}
return false;
}
@Override
public Object getValue() {
// build list of arguments recursively
Object[] args = new Object[function.getArity()];
for (int i = 0; i < function.getArity(); i++) {
args[i] = connections[i].getValue();
}
// return function result
return function.run(args);
}
@Override
public void mutate() {
Resources resources = chromosome.getResources();
// choose to mutate the function or a connection
int geneType = resources.getRandomInt(1 + resources.arity());
// if the int is less than 1, mutate function, else mutate connections
if (geneType < 1) {
setFunction(resources.getRandomFunction());
} else {
// if we decided to mutate connection, subtract 1 from geneType so it fits into the arity range
geneType--;
setConnection(geneType, chromosome.getRandomConnection(column));
}
}
@Override
public String toString() {
return "Node [" + row + ", " + column + "]";
}
}
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