/** Model check a P operator. */
private Result checkExpressionProb(ExpressionProb expr) throws PrismException {
boolean min;
ExpressionTemporal exprTemp;
Expression exprTarget;
BitSet targetLocs;
int timeBound;
boolean timeBoundStrict;
double prob;
// Check whether Pmin=? or Pmax=? (only two cases allowed)
if (expr.getProb() != null) {
throw new PrismException(
"PTA model checking currently only supports Pmin=? and Pmax=? properties (try the digital clocks engine instead)");
}
min = expr.getRelOp().equals("min=");
// Check this is a F path property (only case allowed at the moment)
if (!(expr.getExpression() instanceof ExpressionTemporal))
throw new PrismException(
"PTA model checking currently only supports the F path operator (try the digital clocks engine instead)");
exprTemp = (ExpressionTemporal) expr.getExpression();
if (exprTemp.getOperator() != ExpressionTemporal.P_F || !exprTemp.isSimplePathFormula())
throw new PrismException(
"PTA model checking currently only supports the F path operator (try the digital clocks engine instead)");
// Determine locations satisfying target
exprTarget = exprTemp.getOperand2();
targetLocs = checkLocationExpression(exprTarget);
mainLog.println(
"Target (" + exprTarget + ") satisfied by " + targetLocs.cardinality() + " locations.");
// mainLog.println(targetLocs);
// If there is a time bound, add a clock and encode this into target
if (exprTemp.hasBounds()) {
mainLog.println("Modifying PTA to encode time bound from property...");
// Get time bound info (is always of form <=T or <T)
timeBound = exprTemp.getUpperBound().evaluateInt(constantValues);
timeBoundStrict = exprTemp.upperBoundIsStrict();
// Modify PTA to include time bound; get new target
targetLocs = buildTimeBoundIntoPta(pta, targetLocs, timeBound, timeBoundStrict);
mainLog.println("New PTA: " + pta.infoString());
}
// Compute probability of reaching the set of target locations
prob = computeProbabilisticReachability(targetLocs, min);
// Return result
return new Result(new Double(prob));
}
private static SamplerBoolean createSamplerForProbPathPropertySimple(
Expression expr, ModulesFile mf) throws PrismException {
// Negation/parentheses
if (expr instanceof ExpressionUnaryOp) {
ExpressionUnaryOp exprUnary = (ExpressionUnaryOp) expr;
// Parentheses
if (exprUnary.getOperator() == ExpressionUnaryOp.PARENTH) {
// Recurse
return createSamplerForProbPathPropertySimple(exprUnary.getOperand(), mf);
}
// Negation
else if (exprUnary.getOperator() == ExpressionUnaryOp.NOT) {
// Recurse, then negate meaning
SamplerBoolean sampler = createSamplerForProbPathPropertySimple(exprUnary.getOperand(), mf);
sampler.negate();
return sampler;
}
}
// Temporal operators
else if (expr instanceof ExpressionTemporal) {
ExpressionTemporal exprTemp = (ExpressionTemporal) expr;
// Next
if (exprTemp.getOperator() == ExpressionTemporal.P_X) {
return new SamplerNext(exprTemp);
}
// Until
else if (exprTemp.getOperator() == ExpressionTemporal.P_U) {
if (exprTemp.hasBounds()) {
if (mf.getModelType().continuousTime()) {
// Continuous-time bounded until
return new SamplerBoundedUntilCont(exprTemp);
} else {
// Discrete-time bounded until
return new SamplerBoundedUntilDisc(exprTemp);
}
} else {
// Unbounded until
return new SamplerUntil(exprTemp);
}
}
// Anything else - convert to until and recurse
else {
return createSamplerForProbPathPropertySimple(exprTemp.convertToUntilForm(), mf);
}
}
throw new PrismException("Can't create sampler for property \"" + expr + "\"");
}
