public static void ExportToGv(this MarkovDecisionProcess mdp, TextWriter sb)
{
sb.WriteLine("digraph S {");
//sb.WriteLine("size = \"8,5\"");
sb.WriteLine("node [shape=box];");
var enumerator = mdp.GetEnumerator();
enumerator.SelectInitialDistributions();
var initialStateName = "initialState";
sb.WriteLine($" {initialStateName} [shape=point,width=0.0,height=0.0,label=\"\"];");
ExportDistributionsOfEnumerator(enumerator, initialStateName, sb);
enumerator = mdp.GetEnumerator();
while (enumerator.MoveNextState())
{
var state = enumerator.CurrentState;
sb.Write($" {state} [label=\"{state}\\n(");
for (int i = 0; i < mdp.StateFormulaLabels.Length; i++)
{
if (i > 0)
{
sb.Write(",");
}
sb.Write(mdp.StateLabeling[state][i]);
}
sb.WriteLine(")\"];");
ExportDistributionsOfEnumerator(enumerator, state.ToString(), sb);
}
sb.WriteLine("}");
}
public double CalculateMinimumFinalProbability(double[] initialStateProbabilities)
{
var enumerator = MarkovDecisionProcess.GetEnumerator();
enumerator.SelectInitialDistributions();
//select sum of first distribution
enumerator.MoveNextDistribution();
var sum = 0.0;
while (enumerator.MoveNextTransition())
{
var entry = enumerator.CurrentTransition;
sum += entry.Value * initialStateProbabilities[entry.Column];
}
var finalProbability = sum;
//now find a smaller one
while (enumerator.MoveNextDistribution())
{
sum = 0.0;
while (enumerator.MoveNextTransition())
{
var entry = enumerator.CurrentTransition;
sum += entry.Value * initialStateProbabilities[entry.Column];
}
if (sum < finalProbability)
{
finalProbability = sum;
}
}
return(finalProbability);
}
private void WriteMarkovChainToDisk()
{
_filePrism = new TemporaryFile("prism");
var streamPrism = new StreamWriter(_filePrism.FilePath)
{
NewLine = "\n"
};
MarkovDecisionProcess.ExportToPrism(streamPrism);
}
internal double CalculateMinimumProbabilityToReachStateFormulaInBoundedSteps(Formula psi, int steps)
{
var psiEvaluator = MarkovDecisionProcess.CreateFormulaEvaluator(psi);
var directlySatisfiedStates = CalculateSatisfiedStates(psiEvaluator);
var excludedStates = new Dictionary <int, bool>(); // change for \phi Until \psi
var xnew = MinimumIterator(directlySatisfiedStates, excludedStates, steps);
var finalProbability = CalculateMinimumFinalProbability(xnew);
return(finalProbability);
}
internal double CalculateMinimumProbabilityToReachStateFormula(Formula psi)
{
// same algorithm as CalculateMinimumProbabilityToReachStateFormulaInBoundedSteps with different
// directlySatisfiedStates and excludedStates
var maxSteps = AdjustNumberOfStepsForFactor(50);
var psiEvaluator = MarkovDecisionProcess.CreateFormulaEvaluator(psi);
var directlySatisfiedStates = CalculateSatisfiedStates(psiEvaluator);
var excludedStates = new Dictionary <long, bool>(); // change for \phi Until \psi
var exactlyZeroStates = StatesReachableWithProbabilityExactlyZeroForAtLeastOneScheduler(directlySatisfiedStates, excludedStates);
var exactlyOneStates = SubsetOfStatesReachableWithProbabilityExactlyOneWithAllSchedulers(directlySatisfiedStates, excludedStates); // this algorithm is only an approximation
var xnew = MinimumIterator(exactlyOneStates, exactlyZeroStates, maxSteps);
var finalProbability = CalculateMinimumFinalProbability(xnew);
return(finalProbability);
}
private double CalculateMaximumProbabilityToReachStateFormula(Formula psi)
{
// same algorithm as CalculateMaximumProbabilityToReachStateFormulaInBoundedSteps with different
// directlySatisfiedStates and excludedStates
var maxSteps = 50;
var psiEvaluator = MarkovDecisionProcess.CreateFormulaEvaluator(psi);
var directlySatisfiedStates = CalculateSatisfiedStates(psiEvaluator);
var excludedStates = new Dictionary <int, bool>(); // change for \phi Until \psi
var exactlyZeroStates = StatesReachableWithProbabilityExactlyZeroWithAllSchedulers(directlySatisfiedStates, excludedStates);
var exactlyOneStates = StatesReachableWithProbabilityExactlyOneForAtLeastOneScheduler(directlySatisfiedStates, excludedStates); //cannot perform a better pre calculation
var xnew = MaximumIterator(exactlyOneStates, exactlyZeroStates, maxSteps);
var finalProbability = CalculateMaximumFinalProbability(xnew);
return(finalProbability);
}
public UnderlyingDigraph(MarkovDecisionProcess mdp)
{
//Assumption "every node is reachable" is fulfilled due to the construction
BaseGraph = new BidirectionalGraph <EdgeData>();
var enumerator = mdp.GetEnumerator();
while (enumerator.MoveNextState())
{
while (enumerator.MoveNextDistribution())
{
//find targets of this distribution and create the union. Some possibleSuccessors may be added
while (enumerator.MoveNextTransition())
{
if (enumerator.CurrentTransition.Value > 0.0)
{
BaseGraph.AddVerticesAndEdge(new Edge <EdgeData>(enumerator.CurrentState, enumerator.CurrentTransition.Column, new EdgeData(enumerator.RowOfCurrentDistribution)));
}
}
}
}
}
// Note: Should be used with using(var modelchecker = new ...), otherwise the disposed method may be
// executed by the .net framework directly after using _filePrism.FilePath the last time and the
// file deleted before it could be used by the prism process
public ExternalMdpModelCheckerPrism(MarkovDecisionProcess mdp, TextWriter output = null) : base(mdp, output)
{
WriteMarkovChainToDisk();
}
internal MdpToPrism(MarkovDecisionProcess mdp)
{
_mdp = mdp;
}
internal static void ExportToPrism(this MarkovDecisionProcess mdp, TextWriter sb)
{
var mdpToPrism = new MdpToPrism(mdp);
mdpToPrism.WriteMarkovDecisionProcessToStream(sb);
}
// Note: Should be used with using(var modelchecker = new ...)
public BuiltinMdpModelChecker(MarkovDecisionProcess mdp, TextWriter output = null)
: base(mdp, output)
{
_underlyingDigraph = MarkovDecisionProcess.CreateUnderlyingDigraph();
}
public Dictionary <long, bool> StatesReachableWithProbabilityExactlyOneForAtLeastOneScheduler(Dictionary <long, bool> directlySatisfiedStates,
Dictionary <long, bool> excludedStates)
{
// calculate probabilityExactlyOne (prob1e). There exists a scheduler, for which the probability of
// the resulting states is exactly 1. The result may be different for another scheduler, but at least there exists one.
// This is exact
// The algorithm works this way: It looks at a set of states probabilityMightBeExactlyOne which are initially all states.
// Then it iterates until a fixpoint is found. In each iteration states are removed from probabilityMightBeExactlyOne for
// which a scheduler _must_ switch to a state where the probability is < 1.
// The removal process works this way: In each iteration a backwards search is started.
// A distribution from a predecessor is removed, if not every transition of the distribution leads to a
// state in probabilityMightBeExactlyOne (Reason: It is possible from there to go to a state where probability < 1).
// The fixpoint is the result.
Func <long, bool> nodesToIgnore = excludedStates.ContainsKey;
var probabilityMightBeExactlyOne = CreateComplement(new Dictionary <long, bool>()); //all states
var _isDistributionIncludedCache = new Dictionary <long, bool>();
var mdpEnumerator = MarkovDecisionProcess.GetEnumerator();
Action resetDistributionIncludedCacheForNewIteration = () =>
{
// One possible optimization.
// Only true entries must be deleted because the eligible distributions get less and less each iteration
// On the other hand: Clearing the whole data structure makes the dictionary smaller and access faster.
_isDistributionIncludedCache.Clear();
};
Func <long, bool> isDistributionIncluded = rowOfDistribution =>
{
if (_isDistributionIncludedCache.ContainsKey(rowOfDistribution))
{
return(_isDistributionIncludedCache[rowOfDistribution]);
}
mdpEnumerator.MoveToDistribution(rowOfDistribution);
var includeDistribution = true;
while (includeDistribution && mdpEnumerator.MoveNextTransition())
{
var targetState = mdpEnumerator.CurrentTransition.Column;
// if targetstate is not found in probabilityMightBeExactlyOne then the complete distribution has to be removed
if (!probabilityMightBeExactlyOne.ContainsKey(targetState))
{
includeDistribution = false;
}
}
return(includeDistribution);
};
var fixpointReached = false;
while (!fixpointReached)
{
resetDistributionIncludedCacheForNewIteration();
var ancestorsFound = new Dictionary <long, bool>(); //Note: ancestorsFound must not be reused
// based on DFS https://en.wikipedia.org/wiki/Depth-first_search
var nodesToTraverse = new Stack <long>();
foreach (var node in directlySatisfiedStates)
{
nodesToTraverse.Push(node.Key);
}
while (nodesToTraverse.Count > 0)
{
var currentNode = nodesToTraverse.Pop();
var isIgnored = nodesToIgnore(currentNode);
var alreadyDiscovered = ancestorsFound.ContainsKey(currentNode);
if (!(isIgnored || alreadyDiscovered))
{
ancestorsFound.Add(currentNode, true);
foreach (var inEdge in _underlyingDigraph.BaseGraph.InEdges(currentNode))
{
if (isDistributionIncluded(inEdge.Data.RowOfDistribution))
{
nodesToTraverse.Push(inEdge.Source);
}
}
}
}
if (probabilityMightBeExactlyOne.Count == ancestorsFound.Count)
{
fixpointReached = true;
}
Assert.That(probabilityMightBeExactlyOne.Count >= ancestorsFound.Count, "bug!");
probabilityMightBeExactlyOne = ancestorsFound;
}
return(probabilityMightBeExactlyOne);
}
public Dictionary <long, bool> StatesReachableWithProbabilityExactlyZeroForAtLeastOneScheduler(
Dictionary <long, bool> directlySatisfiedStates, Dictionary <long, bool> excludedStates)
{
// calculate probabilityExactlyZero (prob0e). There exists a scheduler, for which the probability of
// the resulting states is zero. The result may be different for another scheduler, but at least there exists one.
// This is exact
Dictionary <long, bool> ancestorsFound = null;
var probabilityGreaterThanZero = directlySatisfiedStates; //we know initially this is satisfied
var mdpEnumerator = MarkovDecisionProcess.GetEnumerator();
// The idea of the algorithm is to calculate probabilityGreaterThanZero:
// all states where a directlySatisfiedState is reached with a probability > 0
// no matter which scheduler is selected (valid for _all_ adversaries).
// The complement of probabilityGreaterThanZero is the set of states where a scheduler _exists_ for
// which the probability to reach a directlySatisfiedState is exactly 0.
Func <long, bool> nodesToIgnore = source =>
{
//nodes found by UpdateAncestors are always SourceNodes of a edge to an ancestor in ancestorsFound
if (excludedStates.ContainsKey(source))
{
return(false); //source must not be ignored
}
if (directlySatisfiedStates.ContainsKey(source))
{
return(false); //source must not be ignored
}
// must not be cached (, because ancestorsFound might change, even in the same iteration)!!!
// check if _all_ distributions of source contain at least transition to a ancestor in ancestorsFound
mdpEnumerator.SelectSourceState(source);
while (mdpEnumerator.MoveNextDistribution())
{
var foundInDistribution = false;
while (mdpEnumerator.MoveNextTransition() && !foundInDistribution)
{
if (ancestorsFound.ContainsKey(mdpEnumerator.CurrentTransition.Column))
{
foundInDistribution = true;
}
}
if (!foundInDistribution)
{
return(true); // the distribution does not have a targetState in ancestorsFound, so source must be ignored
}
}
return(false); //source must not be ignored
};
// initialize probabilityGreaterThanZero to the states where we initially know the probability is greater than zero
var fixpointReached = false;
while (!fixpointReached)
{
// Calculate fix point of probabilityGreaterThanZero
// Should be finished in one iteration, but I have not proved it yet, so repeat it until fixpoint is reached for sure.
// (The proof relies on details of the algorithm GetAncestors. Intuition: When a state s was not added to the set of
// ancestors it is because one distribution d' has no target state in the ancestors found yet. If the state is in the
// final set of ancestors, the reason is that the state s' of the distribution d', which was responsible for declining
// s has not yet been added to ancestors. When s' is added all its ancestors are traversed again and s is found.)
// Note:
// UpdateAncestors must be used, because nodesToIgnore requires access to the current information about the ancestors
// (ancestorsFound), if it should work in one iteration.
ancestorsFound = new Dictionary <long, bool>();
//Note: We reuse ancestorsFound, which is also known and used by nodesToIgnore. The side effects are on purpose.
// based on DFS https://en.wikipedia.org/wiki/Depth-first_search
var nodesToTraverse = new Stack <long>();
foreach (var node in probabilityGreaterThanZero)
{
nodesToTraverse.Push(node.Key);
}
while (nodesToTraverse.Count > 0)
{
var currentNode = nodesToTraverse.Pop();
var isIgnored = nodesToIgnore(currentNode);
var alreadyDiscovered = ancestorsFound.ContainsKey(currentNode);
if (!(isIgnored || alreadyDiscovered))
{
ancestorsFound.Add(currentNode, true);
foreach (var inEdge in _underlyingDigraph.BaseGraph.InEdges(currentNode))
{
nodesToTraverse.Push(inEdge.Source);
}
}
}
if (probabilityGreaterThanZero.Count == ancestorsFound.Count)
{
fixpointReached = true;
}
probabilityGreaterThanZero = ancestorsFound;
}
var probabilityExactlyZero = CreateComplement(probabilityGreaterThanZero);
return(probabilityExactlyZero);
}
internal double[] MaximumIterator(Dictionary <long, bool> exactlyOneStates, Dictionary <long, bool> exactlyZeroStates, int steps)
{
var stopwatch = new Stopwatch();
stopwatch.Start();
var stateCount = MarkovDecisionProcess.States;
var enumerator = MarkovDecisionProcess.GetEnumerator();
var xold = new double[stateCount];
var xnew = CreateDerivedVector(exactlyOneStates);
var loops = 0;
while (loops < steps)
{
// switch xold and xnew
var xtemp = xold;
xold = xnew;
xnew = xtemp;
loops++;
for (var i = 0; i < stateCount; i++)
{
if (exactlyOneStates.ContainsKey(i))
{
//we could remove this line, because already set by CreateDerivedVector and never changed when we initialize xold with CreateDerivedVector(directlySatisfiedStates)
xnew[i] = 1.0;
}
else if (exactlyZeroStates.ContainsKey(i))
{
//we could remove this line, because already set by CreateDerivedVector and never changed when we initialize xold with CreateDerivedVector(directlySatisfiedStates)
xnew[i] = 0.0;
}
else
{
enumerator.SelectSourceState(i);
//select sum of first distribution
enumerator.MoveNextDistribution();
var sum = 0.0;
while (enumerator.MoveNextTransition())
{
var entry = enumerator.CurrentTransition;
sum += entry.Value * xold[entry.Column];
}
xnew[i] = sum;
//now find a larger one
while (enumerator.MoveNextDistribution())
{
sum = 0.0;
while (enumerator.MoveNextTransition())
{
var entry = enumerator.CurrentTransition;
sum += entry.Value * xold[entry.Column];
}
if (sum > xnew[i])
{
xnew[i] = sum;
}
}
}
}
if (loops % 10 == 0)
{
stopwatch.Stop();
var currentProbability = CalculateMaximumFinalProbability(xnew);
_output?.WriteLine(
$"{loops} Bounded Until iterations in {stopwatch.Elapsed}. Current probability={currentProbability.ToString(CultureInfo.InvariantCulture)}");
stopwatch.Start();
}
}
stopwatch.Stop();
return(xnew);
}
public MarkovDecisionProcessEnumerator(MarkovDecisionProcess mdp)
{
_mdp = mdp;
_matrixEnumerator = mdp.RowsWithDistributions.GetEnumerator();
Reset();
}
// Note: Should be used with using(var modelchecker = new ...)
protected MdpModelChecker(MarkovDecisionProcess mdp, TextWriter output = null)
{
MarkovDecisionProcess = mdp;
_output = output;
}