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Adding simulation reduction rules #487

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Adding simulation reduction rules #487

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26 changes: 19 additions & 7 deletions src/nfa/operations.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,7 @@

#include <algorithm>
#include <list>
#include <string>
#include <unordered_set>

// MATA headers
Expand Down Expand Up @@ -54,10 +55,17 @@ namespace {
return lts_for_simulation.compute_simulation();
}

Nfa reduce_size_by_simulation(const Nfa& aut, StateRenaming &state_renaming) {
Nfa reduce_size_by_simulation(const Nfa& aut, StateRenaming &state_renaming, const std::string& simulation_direction) {
Nfa result;
Nfa aut_m;

if (simulation_direction == "backward")
aut_m = revert(aut);
else
aut_m = aut;

const auto sim_relation = algorithms::compute_relation(
aut, ParameterMap{{ "relation", "simulation"}, { "direction", "forward"}});
aut_m, ParameterMap{{ "relation", "simulation"}, { "direction", "forward"}});

auto sim_relation_symmetric = sim_relation;
sim_relation_symmetric.restrict_to_symmetric();
Expand All @@ -66,7 +74,7 @@ namespace {
std::vector<size_t> quot_proj;
sim_relation_symmetric.get_quotient_projection(quot_proj);

const size_t num_of_states = aut.num_of_states();
const size_t num_of_states = aut_m.num_of_states();

// map each state q of aut to the state of the reduced automaton representing the simulation class of q
for (State q = 0; q < num_of_states; ++q) {
Expand All @@ -83,12 +91,12 @@ namespace {
for (State q = 0; q < num_of_states; ++q) {
const State q_class_state = state_renaming.at(q);

if (aut.initial[q]) { // if a symmetric class contains initial state, then the whole class should be initial
if (aut_m.initial[q]) { // if a symmetric class contains initial state, then the whole class should be initial
result.initial.insert(q_class_state);
}

if (quot_proj[q] == q) { // we process only transitions starting from the representative state, this is enough for simulation
for (const auto &q_trans : aut.delta.state_post(q)) {
for (const auto &q_trans : aut_m.delta.state_post(q)) {
const StateSet representatives_of_states_to = [&]{
StateSet state_set;
for (auto s : q_trans.targets) {
Expand Down Expand Up @@ -117,12 +125,15 @@ namespace {
result.delta.mutable_state_post(q_class_state).insert(SymbolPost(q_trans.symbol, representatives_class_states));
}

if (aut.final[q]) { // if q is final, then all states in its class are final => we make q_class_state final
if (aut_m.final[q]) { // if q is final, then all states in its class are final => we make q_class_state final
result.final.insert(q_class_state);
}
}
}

if (simulation_direction == "backward")
result = revert(result);

return result;
}

Expand Down Expand Up @@ -1147,7 +1158,8 @@ Nfa mata::nfa::reduce(const Nfa &aut, StateRenaming *state_renaming, const Param
std::unordered_map<State,State> reduced_state_map;
const std::string& algorithm = params.at("algorithm");
if ("simulation" == algorithm) {
result = reduce_size_by_simulation(aut, reduced_state_map);
const std::string& simulation_direction = params.at("direction");
result = reduce_size_by_simulation(aut, reduced_state_map, simulation_direction);
}
else if ("residual" == algorithm) {
// reduce type either 'after' or 'with' creation of residual automaton
Expand Down
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