/**
* Performs precomputation before actual state elimination. This handles cases in which all or
* some states can or have to be treated differently, e.g. because there are no target states at
* all, or some states do never reach a target state.
*
* @return true iff state elimination is necessary to obtain a result
*/
private boolean precompute() {
/* if there are no target states, the result is zero everywhere
* for a reachability probability analysis, so all states can be
* made absorbing. If we are performing analysis of accumulated
* rewards, the value will be infinity everywhere. */
if (!pmc.isUseTime() && !pmc.hasTargetStates()) {
for (int state = 0; state < pmc.getNumStates(); state++) {
pmc.makeAbsorbing(state);
if (pmc.isUseRewards()) {
pmc.setReward(state, pmc.getFunctionFactory().getInf());
}
}
return false;
}
/* search for states which might never reach a target state and thus
* have to be assigned a reward of infinity. */
if (pmc.isUseRewards()) {
int[] backStatesArr = collectStatesBackward();
HashSet<Integer> reaching = new HashSet<Integer>();
for (int stateNr = 0; stateNr < backStatesArr.length; stateNr++) {
reaching.add(backStatesArr[stateNr]);
}
for (int state = 0; state < pmc.getNumStates(); state++) {
if (!pmc.isUseTime() && !reaching.contains(state)) {
pmc.setReward(state, pmc.getFunctionFactory().getInf());
}
}
}
return true;
}
