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dtwa_sat_minimize: better selection of the reference automaton

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* src/twaalgos/dtwasat.cc: Choose the reference automaton based on its
size.  With this change, the last example of my LPAR'15 talk goes from
~7s to under 1s.
* NEWS: Mention it.
This commit is contained in:
Alexandre Duret-Lutz 2015-11-24 06:18:18 +01:00
parent a5ca9dbc43
commit a825fa91e5
2 changed files with 47 additions and 8 deletions
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49
src/twaalgos/dtwasat.cc
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@ -1189,6 +1189,39 @@ namespace spot
return res;
}
namespace
{
// Chose a good reference automaton given two automata.
//
// The right automaton only is allowed to be null. In that
// case the left automaton is returned.
//
// The selection relies on the fact that the SAT encoding is
// quadratic in the number of input states, and exponential in the
// number of input sets.
static const_twa_graph_ptr
best_aut(const const_twa_graph_ptr& left,
const const_twa_graph_ptr& right)
{
if (right == nullptr)
return left;
auto lstates = left->num_states();
auto lsets = left->num_sets();
auto rstates = right->num_states();
auto rsets = right->num_sets();
if (lstates <= rstates && lsets <= rsets)
return left;
if (lstates >= rstates && lsets >= rsets)
return right;
long long unsigned lw = (1ULL << lsets) * lstates * lstates;
long long unsigned rw = (1ULL << rsets) * rstates * rstates;
return lw <= rw ? left : right;
}
}
twa_graph_ptr
dtwa_sat_minimize(const const_twa_graph_ptr& a,
unsigned target_acc_number,
@ -1202,10 +1235,10 @@ namespace spot
twa_graph_ptr prev = nullptr;
for (;;)
{
auto next =
dtwa_sat_synthetize(prev ? prev : a, target_acc_number,
target_acc, --n_states,
state_based, colored);
auto src = best_aut(a, prev);
auto next = dtwa_sat_synthetize(src, target_acc_number,
target_acc, --n_states,
state_based, colored);
if (!next)
return prev;
else
@ -1230,10 +1263,10 @@ namespace spot
while (min_states <= max_states)
{
int target = (max_states + min_states) / 2;
auto next =
dtwa_sat_synthetize(prev ? prev : a, target_acc_number,
target_acc, target, state_based,
colored);
auto src = best_aut(a, prev);
auto next = dtwa_sat_synthetize(src, target_acc_number,
target_acc, target, state_based,
colored);
if (!next)
{
min_states = target + 1;