//Finds max visit value within child nodes of referenced Node
public static MonteCarloNode findBestUCTNode(MonteCarloNode _node)
{
//creates a new int parent visit, setting the value to that of the referenced node's state's visit count
int _parentVisit = _node.GetState().GetVisits();
//creates variables used to assist in finding the best UCT node
int _childIndex = 0;
double _uctValue;
double _prevUctValue = int.MinValue;
//loops which iterates for the number of children in the referenced node, finding the best child node with UCT
for (int i = 0; i < _node.GetChildren().Count; i++)
{
//finds the UCT value of the current child node
_uctValue = UCTValue(_parentVisit, _node.GetChildren()[i].GetState().GetScore(), _node.GetChildren()[i].GetState().GetVisits());
//checks if the current UCT value is greater than that of the previous UCT value
if (_uctValue > _prevUctValue)
{
//sets the child index to the index of the current child node
_childIndex = i;
}
//sets the previous UCT value to the current UCT value
_prevUctValue = _uctValue;
}
//returns the child node at the index which produced the best UCT value
return(_node.GetChildren()[_childIndex]);
}
//function used to perform the MCTS Cycle
public void MCTSCycle(MonteCarloNode _rootNode)
{
// Phase 1 - Selection
//finds best node from root node using UCT (Upper Confidence Bound for Trees)
MonteCarloNode _selectionNode = Selection(_rootNode);
// Phase 2 - Expansion
//Checks if the selected node produces a win state, otherwise expanding on the selected node
if (_selectionNode.GetState().GetBoard().CheckStatus() == MonteCarloBoard._inProgress)
{
//Performs expansion on the seleted node
Expansion(_selectionNode);
}
// Phase 3 - Simulation
//sets the node to explore to the selected node
MonteCarloNode _nodeToExplore = _selectionNode;
//checks if the node to explore contains any children
if (_selectionNode.GetChildren().Count > 0)
{
//sets the node to explore to a random child node if any are available
_nodeToExplore = _selectionNode.GetRandomChild();
}
//simulates the node to explore and produces the number of the winner of the simulation, storing the result
int _simulationWinner = Simulation(_nodeToExplore);
// Phase 4 - Update
//backpropagates up the tree, updating node scores from the node to explore to root based upon the winner of the simulation
Backpropogation(_nodeToExplore, _simulationWinner);
}
//function used to perform the selection of the MCTS cycle
private MonteCarloNode Selection(MonteCarloNode _rootNode)
{
//sets a new node variable to the root node passed through
MonteCarloNode _UCTnode = _rootNode;
//checks if the node contains any child nodes
while (_UCTnode.GetChildren().Count != 0)
{
//finds the best child node using UCT (Upper Confidence Bound for Trees) of the current node, then updates the node
//this is looped while the node contains children, finding the best child node with no more child nodes
_UCTnode = MonteCarloUCT.findBestUCTNode(_UCTnode);
}
//the UCT node is returned
return(_UCTnode);
}
public MonteCarloNode(MonteCarloNode _newNode)
{
this._children = new List <MonteCarloNode>();
this._state = new MonteCarloState(_newNode.GetState());
if (_newNode.GetParent() != null)
{
this._parent = _newNode.GetParent();
}
List <MonteCarloNode> _nodeChildren = _newNode.GetChildren();
foreach (MonteCarloNode _child in _nodeChildren)
{
this._children.Add(new MonteCarloNode(_child));
}
}
//function used to perform expansion of the MCTS cycle
private void Expansion(MonteCarloNode _nodeToExpand)
{
//finds all legal states for the current node
List <MonteCarloState> _legalStates = _nodeToExpand.GetState().GetLegalStates();
//loops through each legal state found
foreach (MonteCarloState _state in _legalStates)
{
//creates a new node, setting it's state to a legal state found
MonteCarloNode _newNode = new MonteCarloNode(_state);
//sets the parent as the node to expand as passed through
_newNode.SetParent(_nodeToExpand);
//adds the new node to the child array of the node to expand
_nodeToExpand.GetChildren().Add(_newNode);
}
}
public void addChild(MonteCarloNode _parent, MonteCarloNode _child)
{
_parent.GetChildren().Add(_child);
}