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Make dtmc model checker throw on unreachable condition when checking conditional probabilities. #946

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Make dtmc model checker throw on unreachable condition when checking conditional probabilities. #946

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e0487be
Make dtmc model checker throw on unreachable condition.
lukovdm Jul 1, 2026
5f8696b
Change exception type
lukovdm Jul 1, 2026
2831573
Add better condition reachable check.
lukovdm Aug 20, 2026
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1 change: 1 addition & 0 deletions resources/examples/testfiles/dtmc/test_conditional.pm
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Expand Up @@ -14,5 +14,6 @@ rewards
s=2 : 1;
endrewards

label "unreachable" = false;
label "condition" = s=2;
label "target" = s=3;
24 changes: 24 additions & 0 deletions resources/examples/testfiles/dtmc/test_conditional_multiple_initial.pm
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@@ -0,0 +1,24 @@
dtmc

module test
s : [0 .. 3];

[] s=0 -> 0.5 : (s'=1) + 0.5 : (s'=2);
[] s=1 -> 1 : true;
[] s=2 -> 1 : (s'=3);
[] s=3 -> 1 : true;

endmodule

// The condition is reachable from state 0, but not from state 1.
init
s=0 | s=1
endinit

rewards
s=2 : 1;
endrewards

label "start" = s=0;
label "condition" = s=2;
label "target" = s=3;
3 changes: 2 additions & 1 deletion src/storm/modelchecker/helper/conditional/ConditionalHelper.cpp
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Expand Up @@ -8,6 +8,7 @@
#include "storm/environment/modelchecker/ConditionalModelCheckerEnvironment.h"
#include "storm/environment/modelchecker/ModelCheckerEnvironment.h"
#include "storm/environment/solver/MinMaxSolverEnvironment.h"
#include "storm/exceptions/InvalidPropertyException.h"
#include "storm/exceptions/NotImplementedException.h"
#include "storm/exceptions/NotSupportedException.h"
#include "storm/modelchecker/prctl/helper/SparseMdpPrctlHelper.h"
Expand Down Expand Up @@ -1252,7 +1253,7 @@ std::optional<SolutionType> handleTrivialCases(uint64_t const initialState, Norm
if (normalForm.conditionStates.get(initialState)) {
return normalForm.getTargetValue(initialState); // The value is already known, nothing to do.
} else {
STORM_LOG_THROW(!normalForm.universalObservationFailureStates.get(initialState), storm::exceptions::NotSupportedException,
STORM_LOG_THROW(!normalForm.universalObservationFailureStates.get(initialState), storm::exceptions::InvalidPropertyException,
"Trying to compute undefined conditional probability: the condition has probability 0 under all policies.");
// The last case for a terminal initial state is that it is already target and the condition is reachable with non-zero probability.
// In this case, all schedulers induce a conditional probability of 1 (or do not reach the condition, i.e., have undefined value)
Expand Down
102 changes: 55 additions & 47 deletions src/storm/modelchecker/prctl/helper/SparseDtmcPrctlHelper.cpp
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Expand Up @@ -858,35 +858,39 @@ std::vector<SolutionType> SparseDtmcPrctlHelper<ValueType, RewardModelType, Solu
if constexpr (storm::IsIntervalType<ValueType>) {
STORM_LOG_THROW(false, storm::exceptions::NotImplementedException, "We do not support computing conditional probabilities with interval models.");
} else {
// The conditional value is only defined for states that reach the condition with positive probability.
storm::storage::BitVector const conditionProbGreater0States =
storm::utility::graph::performProbGreater0(backwardTransitions, storm::storage::BitVector(conditionStates.size(), true), conditionStates);
STORM_LOG_THROW(goal.hasRelevantValues() ? goal.relevantValues().isSubsetOf(conditionProbGreater0States) : !conditionProbGreater0States.empty(),
storm::exceptions::InvalidPropertyException, "Trying to compute an undefined conditional value: the condition is not reachable.");

// Prepare result vector.
std::vector<ValueType> result(transitionMatrix.getRowCount(), storm::utility::infinity<ValueType>());

if (!conditionStates.empty()) {
BaierTransformedModel transformedModel =
computeBaierTransformation(env, transitionMatrix, backwardTransitions, targetStates, conditionStates, boost::none);

if (transformedModel.noTargetStates) {
storm::utility::vector::setVectorValues(result, transformedModel.beforeStates, storm::utility::zero<ValueType>());
BaierTransformedModel transformedModel =
computeBaierTransformation(env, transitionMatrix, backwardTransitions, targetStates, conditionStates, boost::none);

if (transformedModel.noTargetStates) {
storm::utility::vector::setVectorValues(result, transformedModel.beforeStates, storm::utility::zero<ValueType>());
} else {
// At this point, we do not need to check whether there are 'before' states, since the condition
// states were non-empty so there is at least one state with a positive probability of satisfying
// the condition.

// Now compute reachability probabilities in the transformed model.
storm::storage::SparseMatrix<ValueType> const& newTransitionMatrix = transformedModel.transitionMatrix.get();
storm::storage::BitVector newRelevantValues;
if (goal.hasRelevantValues()) {
newRelevantValues = transformedModel.getNewRelevantStates(goal.relevantValues());
} else {
// At this point, we do not need to check whether there are 'before' states, since the condition
// states were non-empty so there is at least one state with a positive probability of satisfying
// the condition.

// Now compute reachability probabilities in the transformed model.
storm::storage::SparseMatrix<ValueType> const& newTransitionMatrix = transformedModel.transitionMatrix.get();
storm::storage::BitVector newRelevantValues;
if (goal.hasRelevantValues()) {
newRelevantValues = transformedModel.getNewRelevantStates(goal.relevantValues());
} else {
newRelevantValues = transformedModel.getNewRelevantStates();
}
goal.setRelevantValues(std::move(newRelevantValues));
std::vector<ValueType> conditionalProbabilities = computeUntilProbabilities(
env, std::move(goal), newTransitionMatrix, newTransitionMatrix.transpose(),
storm::storage::BitVector(newTransitionMatrix.getRowCount(), true), transformedModel.targetStates.get(), qualitative);

storm::utility::vector::setVectorValues(result, transformedModel.beforeStates, conditionalProbabilities);
newRelevantValues = transformedModel.getNewRelevantStates();
}
goal.setRelevantValues(std::move(newRelevantValues));
std::vector<ValueType> conditionalProbabilities =
computeUntilProbabilities(env, std::move(goal), newTransitionMatrix, newTransitionMatrix.transpose(),
storm::storage::BitVector(newTransitionMatrix.getRowCount(), true), transformedModel.targetStates.get(), qualitative);

storm::utility::vector::setVectorValues(result, transformedModel.beforeStates, conditionalProbabilities);
}

return result;
Expand All @@ -901,34 +905,38 @@ std::vector<SolutionType> SparseDtmcPrctlHelper<ValueType, RewardModelType, Solu
if constexpr (storm::IsIntervalType<ValueType>) {
STORM_LOG_THROW(false, storm::exceptions::NotImplementedException, "We do not support computing conditional rewards with interval models.");
} else {
// The conditional value is only defined for states that reach the condition with positive probability.
storm::storage::BitVector const conditionProbGreater0States =
storm::utility::graph::performProbGreater0(backwardTransitions, storm::storage::BitVector(conditionStates.size(), true), conditionStates);
STORM_LOG_THROW(goal.hasRelevantValues() ? goal.relevantValues().isSubsetOf(conditionProbGreater0States) : !conditionProbGreater0States.empty(),
storm::exceptions::InvalidPropertyException, "Trying to compute an undefined conditional value: the condition is not reachable.");

// Prepare result vector.
std::vector<ValueType> result(transitionMatrix.getRowCount(), storm::utility::infinity<ValueType>());

if (!conditionStates.empty()) {
BaierTransformedModel transformedModel = computeBaierTransformation(env, transitionMatrix, backwardTransitions, targetStates, conditionStates,
rewardModel.getTotalRewardVector(transitionMatrix));

if (transformedModel.noTargetStates) {
storm::utility::vector::setVectorValues(result, transformedModel.beforeStates, storm::utility::zero<ValueType>());
BaierTransformedModel transformedModel = computeBaierTransformation(env, transitionMatrix, backwardTransitions, targetStates, conditionStates,
rewardModel.getTotalRewardVector(transitionMatrix));

if (transformedModel.noTargetStates) {
storm::utility::vector::setVectorValues(result, transformedModel.beforeStates, storm::utility::zero<ValueType>());
} else {
// At this point, we do not need to check whether there are 'before' states, since the condition
// states were non-empty so there is at least one state with a positive probability of satisfying
// the condition.

// Now compute reachability probabilities in the transformed model.
storm::storage::SparseMatrix<ValueType> const& newTransitionMatrix = transformedModel.transitionMatrix.get();
storm::storage::BitVector newRelevantValues;
if (goal.hasRelevantValues()) {
newRelevantValues = transformedModel.getNewRelevantStates(goal.relevantValues());
} else {
// At this point, we do not need to check whether there are 'before' states, since the condition
// states were non-empty so there is at least one state with a positive probability of satisfying
// the condition.

// Now compute reachability probabilities in the transformed model.
storm::storage::SparseMatrix<ValueType> const& newTransitionMatrix = transformedModel.transitionMatrix.get();
storm::storage::BitVector newRelevantValues;
if (goal.hasRelevantValues()) {
newRelevantValues = transformedModel.getNewRelevantStates(goal.relevantValues());
} else {
newRelevantValues = transformedModel.getNewRelevantStates();
}
goal.setRelevantValues(std::move(newRelevantValues));
std::vector<ValueType> conditionalRewards =
computeReachabilityRewards(env, std::move(goal), newTransitionMatrix, newTransitionMatrix.transpose(), transformedModel.stateRewards.get(),
transformedModel.targetStates.get(), qualitative);
storm::utility::vector::setVectorValues(result, transformedModel.beforeStates, conditionalRewards);
newRelevantValues = transformedModel.getNewRelevantStates();
}
goal.setRelevantValues(std::move(newRelevantValues));
std::vector<ValueType> conditionalRewards =
computeReachabilityRewards(env, std::move(goal), newTransitionMatrix, newTransitionMatrix.transpose(), transformedModel.stateRewards.get(),
transformedModel.targetStates.get(), qualitative);
storm::utility::vector::setVectorValues(result, transformedModel.beforeStates, conditionalRewards);
}

return result;
Expand Down
54 changes: 54 additions & 0 deletions src/test/storm/modelchecker/prctl/dtmc/ConditionalDtmcPrctlModelCheckerTest.cpp
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Expand Up @@ -7,6 +7,7 @@
#include "storm/environment/solver/EigenSolverEnvironment.h"
#include "storm/environment/solver/GmmxxSolverEnvironment.h"
#include "storm/environment/solver/NativeSolverEnvironment.h"
#include "storm/exceptions/InvalidPropertyException.h"
#include "storm/logic/Formulas.h"
#include "storm/modelchecker/prctl/SparseDtmcPrctlModelChecker.h"
#include "storm/modelchecker/results/ExplicitQuantitativeCheckResult.h"
Expand Down Expand Up @@ -165,6 +166,10 @@ TYPED_TEST(ConditionalDtmcPrctlModelCheckerTest, Conditional) {
storm::modelchecker::ExplicitQuantitativeCheckResult<ValueType>& quantitativeResult2 = result->asExplicitQuantitativeCheckResult<ValueType>();
EXPECT_NEAR(storm::utility::one<ValueType>(), quantitativeResult2[0], this->precision());

formula = formulaParser.parseSingleFormulaFromString("P=? [F \"target\" || F \"unreachable\"]");

STORM_SILENT_EXPECT_THROW(checker.check(this->env(), *formula), storm::exceptions::InvalidPropertyException);

formula = formulaParser.parseSingleFormulaFromString("R=? [F \"target\"]");

result = checker.check(this->env(), *formula);
Expand All @@ -176,5 +181,54 @@ TYPED_TEST(ConditionalDtmcPrctlModelCheckerTest, Conditional) {
result = checker.check(this->env(), *formula);
storm::modelchecker::ExplicitQuantitativeCheckResult<ValueType>& quantitativeResult4 = result->asExplicitQuantitativeCheckResult<ValueType>();
EXPECT_NEAR(storm::utility::one<ValueType>(), quantitativeResult4[0], this->precision());

formula = formulaParser.parseSingleFormulaFromString("R=? [F \"target\" || F \"unreachable\"]");

STORM_SILENT_EXPECT_THROW(checker.check(this->env(), *formula), storm::exceptions::InvalidPropertyException);
}

TYPED_TEST(ConditionalDtmcPrctlModelCheckerTest, ConditionalUnreachableFromInitialState) {
typedef typename TestFixture::ValueType ValueType;

// In this model, the condition is reachable from one of the two initial states only.
storm::prism::Program program = storm::parser::PrismParser::parse(STORM_TEST_RESOURCES_DIR "/dtmc/test_conditional_multiple_initial.pm");

storm::generator::NextStateGeneratorOptions options;
options.setBuildAllLabels().setBuildAllRewardModels();
std::shared_ptr<storm::models::sparse::Model<ValueType>> model = storm::builder::ExplicitModelBuilder<ValueType>(program, options).build();
ASSERT_TRUE(model->getType() == storm::models::ModelType::Dtmc);
ASSERT_EQ(4ul, model->getNumberOfStates());

std::shared_ptr<storm::models::sparse::Dtmc<ValueType>> dtmc = model->template as<storm::models::sparse::Dtmc<ValueType>>();
ASSERT_EQ(2ul, dtmc->getInitialStates().getNumberOfSetBits());
storm::storage::BitVector initialStatesWithoutCondition = dtmc->getInitialStates() & ~dtmc->getStates("start");
ASSERT_EQ(1ul, initialStatesWithoutCondition.getNumberOfSetBits());

storm::modelchecker::SparseDtmcPrctlModelChecker<storm::models::sparse::Dtmc<ValueType>> checker(*dtmc);

auto expManager = std::make_shared<storm::expressions::ExpressionManager>();
storm::parser::FormulaParser formulaParser(expManager);

std::shared_ptr<storm::logic::Formula const> formula = formulaParser.parseSingleFormulaFromString("P=? [F \"target\" || F \"condition\"]");

// If we are only interested in the initial states, the value is undefined for the initial state that cannot reach the condition.
STORM_SILENT_EXPECT_THROW(checker.check(this->env(), storm::modelchecker::CheckTask<storm::logic::Formula, ValueType>(*formula, true)),
storm::exceptions::InvalidPropertyException);

// If all states are relevant, the undefined values are reported as infinity.
std::unique_ptr<storm::modelchecker::CheckResult> result = checker.check(this->env(), *formula);
storm::modelchecker::ExplicitQuantitativeCheckResult<ValueType>& quantitativeResult1 = result->asExplicitQuantitativeCheckResult<ValueType>();
EXPECT_NEAR(storm::utility::one<ValueType>(), quantitativeResult1[*dtmc->getStates("start").begin()], this->precision());
EXPECT_EQ(storm::utility::infinity<ValueType>(), quantitativeResult1[*initialStatesWithoutCondition.begin()]);

formula = formulaParser.parseSingleFormulaFromString("R=? [F \"target\" || F \"condition\"]");

STORM_SILENT_EXPECT_THROW(checker.check(this->env(), storm::modelchecker::CheckTask<storm::logic::Formula, ValueType>(*formula, true)),
storm::exceptions::InvalidPropertyException);

result = checker.check(this->env(), *formula);
storm::modelchecker::ExplicitQuantitativeCheckResult<ValueType>& quantitativeResult2 = result->asExplicitQuantitativeCheckResult<ValueType>();
EXPECT_NEAR(storm::utility::one<ValueType>(), quantitativeResult2[*dtmc->getStates("start").begin()], this->precision());
EXPECT_EQ(storm::utility::infinity<ValueType>(), quantitativeResult2[*initialStatesWithoutCondition.begin()]);
}
} // namespace
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