Commit 4be7065b authored by Alexandre Duret-Lutz's avatar Alexandre Duret-Lutz
Browse files

simulation: speedup on deterministic automata

* spot/twaalgos/ Detect deterministic automata, and skip
the partial-order update.
* NEWS: Mention the speedup.
parent 6ca555ed
......@@ -13,6 +13,11 @@ New in spot (not yet released)
not used. In particular, this helps scc_info to be more efficient
at deciding the acceptance of SCCs in presence of Fin acceptance.
* Simulation-based reductions now implement just bisimulations-based
reduction on deterministic automata, to save time. As an example,
this halves the run time of
genltl --rv-counter=10 | ltl2tgba
New in spot 2.1.2 (2016-10-14)
Command-line tools:
......@@ -29,58 +29,29 @@
#include <spot/twaalgos/sccfilter.hh>
#include <spot/twaalgos/sccinfo.hh>
#include <spot/twaalgos/sepsets.hh>
#include <spot/twaalgos/isdet.hh>
#include <spot/misc/bddlt.hh>
// The way we developed this algorithm is the following: We take an
// automaton, and reverse all these acceptance conditions. We reverse
// them to go make the meaning of the signature easier. We are using
// bdd, and we want to let it make all the simplification. Because of
// the format of the acceptance condition, it doesn't allow easy
// simplification. Instead of encoding them as: "a!b!c + !ab!c", we
// use them as: "ab". We complement them because we want a
// simplification if the condition of the edge A implies the
// edge of B, and if the acceptance condition of A is included
// in the acceptance condition of B. To let the bdd makes the job, we
// revert them.
// Then, to check if a edge i-dominates another, we'll use the bdd:
// "sig(transA) = cond(trans) & acc(trans) & implied(class(trans->state))"
// Idem for sig(transB). The 'implied'
// (represented by a hash table 'relation_' in the implementation) is
// a conjunction of all the class dominated by the class of the
// destination. This is how the relation is included in the
// signature. It makes the simplifications alone, and the work is
// done. The algorithm is cut into several step:
// Simulation-based reduction, implemented using bdd-based signatures.
// 1. Run through the tgba and switch the acceptance condition to their
// negation, and initializing relation_ by the 'init_ -> init_' where
// init_ is the bdd which represents the class. This function is the
// constructor of Simulation.
// 2. Enter in the loop (run).
// - Rename the class.
// - run through the automaton and computing the signature of each
// state. This function is `update_sig'.
// - Enter in a double loop to adapt the partial order, and set
// 'relation_' accordingly.
// 3. Rename the class (to actualize the name in the previous_class and
// in relation_).
// 4. Building an automaton with the result, with the condition:
// "a edge in the original automaton appears in the simulated one
// iff this edge is included in the set of i-maximal neighbour."
// This function is `build_output'.
// The automaton simulated is recomplemented to come back to its initial
// state when the object Simulation is destroyed.
// The signature of a state is a Boolean function (implemented as a
// BDD) representing the set of outgoing transitions of that state.
// Two states with the same signature are equivalent and can be
// merged.
// Obviously these functions are possibly cut into several little ones.
// This is just the general development idea.
// We define signatures in a way that implications between signatures
// entail language inclusion. These inclusions are used to remove
// redundant transitions, but this occurs implicitly while
// transforming the signature into irredundant-sum-of-product before
// building the automaton: redundant terms that are left over
// correspond to ignored transitions.
// See our Spin'13 paper for background on this procedure.
namespace spot
// Some useful typedef:
// Used to get the signature of the state.
typedef std::vector<bdd> vector_state_bdd;
......@@ -88,12 +59,9 @@ namespace spot
typedef std::map<bdd, std::list<unsigned>,
bdd_less_than> map_bdd_lstate;
typedef std::map<bdd, unsigned, bdd_less_than> map_bdd_state;
// This class helps to compare two automata in term of
// size.
struct automaton_size
struct automaton_size final
: edges(0),
......@@ -251,6 +219,8 @@ namespace spot
assert(a_->num_states() == size_a_);
want_implications_ = !is_deterministic(a_);
// Now, we have to get the bdd which will represent the
// class. We register one bdd by state, because in the worst
// case, |Class| == |State|.
......@@ -447,16 +417,17 @@ namespace spot
bdd n_sig = now_to_next[n].first;
bdd n_class = now_to_next[n].second;
for (unsigned m = 0; m < sz; ++m)
if (n == m)
if (bdd_implies(n_sig, now_to_next[m].first))
n_class &= now_to_next[m].second;
if (want_implications_)
for (unsigned m = 0; m < sz; ++m)
if (n == m)
if (bdd_implies(n_sig, now_to_next[m].first))
n_class &= now_to_next[m].second;
relation_[now_to_next[n].second] = n_class;
......@@ -621,8 +592,8 @@ namespace spot
// and "unambiguous" property preserved
true, // stutter inv.
if (nb_minato == nb_satoneset && !Cosimulation)
if (!Cosimulation)
res->prop_deterministic(nb_minato == nb_satoneset);
if (Sba)
return res;
......@@ -686,6 +657,10 @@ namespace spot
// Used to know when there is no evolution in the partial order.
unsigned int po_size_;
// Whether to compute implications between classes. This is costly
// and useless for deterministic automata.
bool want_implications_;
// All the class variable:
bdd all_class_var_;
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