public Pair <MDPUtilityFunction <TState>, Double> ValueIterateOnce(
double gamma, MDPUtilityFunction <TState> presentUtilityFunction)
{
var maxUtilityGrowth = 0.0;
var newUtilityFunction = new MDPUtilityFunction <TState>();
foreach (TState s in nonFinalstates)
{
// TODO: figure out what to do with commented out code
// double utility = rewardFunction.getRewardFor(s)
// + (gamma * highestUtilityTransition.getSecond());
var utility = this.ValueIterateOnceForGivenState(gamma,
presentUtilityFunction, s);
var differenceInUtility = Math.Abs(utility
- presentUtilityFunction.GetUtility(s));
if (differenceInUtility > maxUtilityGrowth)
{
maxUtilityGrowth = differenceInUtility;
}
newUtilityFunction.SetUtility(s, utility);
foreach (var state in terminalStates)
{
newUtilityFunction.SetUtility(state, presentUtilityFunction
.GetUtility(state));
}
}
return(new Pair <MDPUtilityFunction <TState>, Double>(
newUtilityFunction, maxUtilityGrowth));
}
private Dictionary <TAction, Double> GetExpectedUtilityForSelectedTransitions(
IList <MDPTransition <TState, TAction> > transitions,
MDPUtilityFunction <TState> uf)
{
var actionsToUtilities = new Dictionary <TAction, double>();
foreach (var triplet in transitions)
{
var s = triplet.GetInitialState();
var action = triplet.GetAction();
var destinationState = triplet.GetDestinationState();
var probabilityOfTransition = this.GetTransitionProbability(s,
action, destinationState);
var expectedUtility = (probabilityOfTransition * uf
.GetUtility(destinationState));
if (!actionsToUtilities.ContainsKey(action))
{
actionsToUtilities[action] = expectedUtility;
}
else
{
actionsToUtilities[action] = actionsToUtilities[action] + expectedUtility;
}
}
return(actionsToUtilities);
}
public MDPUtilityFunction <TState> Copy()
{
var other = new MDPUtilityFunction <TState>();
foreach (TState state in hash.Keys)
{
other.SetUtility(state, hash[state]);
}
return(other);
}
public MDPUtilityFunction <TState> AsUtilityFunction()
{
var uf = new MDPUtilityFunction <TState>();
foreach (TState state in stateToReward.Keys)
{
uf.SetUtility(state, this.GetRewardFor(state));
}
return(uf);
}
private double ValueIterateOnceForGivenState(double gamma,
MDPUtilityFunction <TState> presentUtilityFunction,
TState state)
{
var highestUtilityTransition = transitionModel
.GetTransitionWithMaximumExpectedUtility(state,
presentUtilityFunction);
var utility = rewardFunction.GetRewardFor(state)
+ (gamma * highestUtilityTransition.GetSecond());
return(utility);
}
public MDPUtilityFunction <TState> PolicyEvaluation(
MDPPolicy <TState, TAction> pi,
MDPUtilityFunction <TState> u, double gamma, int iterations)
{
var uDash = u.Copy();
for (var i = 0; i < iterations; i++)
{
uDash = this.ValueIterateOnceWith(gamma, pi, uDash);
}
return(uDash);
}
public Pair <TAction, double> GetTransitionWithMaximumExpectedUtility(
TState s, MDPUtilityFunction <TState> uf)
{
if ((IsTerminal(s)))
{
return(new Pair <TAction, Double>(null, 0.0));
}
var transitionsStartingWithS = this.GetTransitionsStartingWith(s);
Dictionary <TAction, double> actionsToUtilities = GetExpectedUtilityForSelectedTransitions(transitionsStartingWithS, uf);
return(GetActionWithMaximumUtility(actionsToUtilities));
}
public Pair <TAction, double> GetTransitionWithMaximumExpectedUtilityUsingPolicy(
MDPPolicy <TState, TAction> policy, TState s,
MDPUtilityFunction <TState> uf)
{
if ((IsTerminal(s)))
{
return(new Pair <TAction, Double>(null, 0.0));
}
var transitionsWithStartingStateSAndActionFromPolicy = this.GetTransitionsWithStartingStateAndAction(
s, policy.GetAction(s));
Dictionary <TAction, Double> actionsToUtilities = GetExpectedUtilityForSelectedTransitions(
transitionsWithStartingStateSAndActionFromPolicy, uf);
return(this.GetActionWithMaximumUtility(actionsToUtilities));
}
private MDPUtilityFunction <TState> ValueIterateOnceWith(double gamma,
MDPPolicy <TState, TAction> pi,
MDPUtilityFunction <TState> U)
{
MDPUtilityFunction <TState> uDash = U.Copy();
foreach (var s in this.nonFinalstates)
{
var highestPolicyTransition =
this.transitionModel.GetTransitionWithMaximumExpectedUtilityUsingPolicy(pi, s, U);
double utility = rewardFunction.GetRewardFor(s)
+ (gamma * highestPolicyTransition.GetSecond());
uDash.SetUtility(s, utility);
}
// TODO: debugging code
// System.out.println("ValueIterationOnce before " + U);
// System.out.println("ValueIterationOnce after " + U_dash);
return(uDash);
}
