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* src/tgba/tgbabddconcrete.cc (set_init_state, succ_iter): Make

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sure to compute the status of the most Now variables possible.
This helps to identify equivalant states.
(tgba_bdd_concrete): Call set_init_state.
This commit is contained in:
Alexandre Duret-Lutz 2003-06-12 15:21:33 +00:00
parent fe6ca2a7a4
commit 5d2e0a4224
2 changed files with 58 additions and 1 deletions
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7
ChangeLog
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@ -1,3 +1,10 @@
2003-06-12 Alexandre Duret-Lutz <aduret@src.lip6.fr>
* src/tgba/tgbabddconcrete.cc (set_init_state, succ_iter): Make
sure to compute the status of the most Now variables possible.
This helps to identify equivalant states.
(tgba_bdd_concrete): Call set_init_state.
2003-06-10 Alexandre Duret-Lutz <aduret@src.lip6.fr>
* src/tgba/ltl2tgba.cc (ltl_trad_visitor::visit): Handle F and G.

52
src/tgba/tgbabddconcrete.cc
View file

@ -10,8 +10,9 @@ namespace spot
}
tgba_bdd_concrete::tgba_bdd_concrete(const tgba_bdd_factory& fact, bdd init)
: data_(fact.get_core_data()), dict_(fact.get_dict()), init_(init)
: data_(fact.get_core_data()), dict_(fact.get_dict())
{
set_init_state(init);
}
tgba_bdd_concrete::~tgba_bdd_concrete()
@ -21,6 +22,40 @@ namespace spot
void
tgba_bdd_concrete::set_init_state(bdd s)
{
// Usually, the ltl2tgba translator will return an
// initial state which does not include all true Now variables,
// even though the truth of some Now variables is garanteed.
//
// For instance, when building the automata for the formula GFa,
// the translator will define the following two equivalences
// Now[Fa] <=> a | (Prom[a] & Next[Fa])
// Now[GFa] <=> Now[Fa] & Next[GFa]
// and return Now[GFa] as initial state.
//
// Starting for state Now[GFa], we could then build
// the following automaton:
// In state Now[GFa]:
// if `a', go to state Now[GFa]
// if True, go to state Now[GFa] & Now[Fa] with Prom[a]
// In state Now[GFa] & Now[Fa]:
// if `a', go to state Now[GFa]
// if True, go to state Now[GFa] & Now[Fa] with Prom[a]
//
// As we can see, states Now[GFa] and Now[GFa] & Now[Fa] share
// the same actions. This is no surprise, because
// Now[GFa] <=> Now[GFa] & Now[Fa] according to the equivalences
// defined by the translator.
//
// What sounds bogus is that we dissociated the two states:
// there should be only one, so that the automaton become
//
// In state Now[GFa] & Now[Fa]:
// if `a', go to state Now[GFa] & Now[GFa]
// if True, go to state Now[GFa] & Now[Fa] with Prom[a]
//
// To achieve this, we immerse the state into the relation
// to collect the status of other Now variables.
s &= bdd_relprod(s, data_.relation, data_.notnow_set);
init_ = s;
}
@ -44,6 +79,21 @@ namespace spot
bdd succ_set = bdd_replace(bdd_exist(data_.relation & s->as_bdd(),
data_.now_set),
data_.next_to_now);
// Immerse known Now variables into the relation to compute the
// status of any other Now variables. See the comment in
// set_init_state for the rational. Note that unlike
// set_init_state, we work only from the Now variables, not from
// any other atomic propositions around. This is because the Now
// variables and the atomic propositions do not correspond to the
// same instant: atomic propositions describe what we must verify
// now while Now variables describe the state where we go (and
// where something else we have to be checked) -- actually these
// Now variables are really Next variables renammed for
// convenience.
succ_set &= bdd_relprod(bdd_exist(succ_set, data_.notnow_set),
data_.relation, data_.notnow_set);
return new tgba_succ_iterator_concrete(data_, succ_set);
}