Commit 601e1405 authored by Thibaud Michaud's avatar Thibaud Michaud
Browse files

parity game: compute winning strategy

* spot/misc/game.cc, spot/misc/game.hh: Here.
* bin/ltlsynt.cc: Realizability is now done by checking if the winning
strategy contains the initial state.
parent f414e9f5
......@@ -213,7 +213,7 @@ namespace
{
case REC:
{
if (pg.winner())
if (std::get<0>(pg.solve()).count(pg.get_init_state_number()))
std::cout << "REALIZABLE\n";
else
std::cout << "UNREALIZABLE\n";
......
......@@ -54,14 +54,14 @@ void parity_game::print(std::ostream& os)
}
}
bool parity_game::winner() const
std::pair<parity_game::region_t, parity_game::strategy_t>
parity_game::solve() const
{
std::unordered_set<unsigned> states_;
region_t states_;
for (unsigned i = 0; i < num_states(); ++i)
states_.insert(i);
unsigned m = max_parity();
auto w1 = winning_region(states_, m);
return w1.find(get_init_state_number()) != w1.end();
return solve_rec(states_, m);
}
bool parity_game::solve_qp() const
......@@ -69,94 +69,111 @@ bool parity_game::solve_qp() const
return reachability_game(*this).is_reachable();
}
void parity_game::attractor(const std::unordered_set<unsigned>& subgame,
std::unordered_set<unsigned>& set,
unsigned max_parity, bool odd,
bool attr_max) const
parity_game::strategy_t
parity_game::attractor(const region_t& subgame, region_t& set,
unsigned max_parity, bool odd, bool attr_max) const
{
strategy_t strategy;
unsigned size;
std::unordered_set<unsigned> complement = subgame;
std::unordered_set<unsigned> delta = set;
do
{
size = set.size();
for (unsigned s: subgame)
for (unsigned s: delta)
complement.erase(s);
for (unsigned s: complement)
{
bool any = false;
bool all = true;
unsigned i = 0;
for (auto& e: out(s))
{
if (e.acc.max_set() - 1 <= max_parity
&& subgame.find(e.dst) != subgame.end())
if (e.acc.max_set() - 1 <= max_parity && subgame.count(e.dst))
{
if (set.find(e.dst) != set.end()
if (set.count(e.dst)
|| (attr_max && e.acc.max_set() - 1 == max_parity))
any = true;
{
if (!any && owner_[s] && odd)
strategy[s] = i;
any = true;
}
else
all = false;
}
++i;
}
if ((owner_[s] == odd && any) || (owner_[s] != odd && all))
set.insert(s);
{
set.insert(s);
delta.insert(s);
}
}
} while (set.size() != size);
return strategy;
}
std::unordered_set<unsigned>
parity_game::winning_region(std::unordered_set<unsigned>& subgame,
unsigned max_parity) const
auto parity_game::solve_rec(region_t& subgame, unsigned max_parity) const
-> std::pair<region_t, strategy_t>
{
// The algorithm works recursively on subgames. To avoid useless copies of
// the game at each call, subgame and max_parity are used to filter states
// and transitions.
if (max_parity == 0 || subgame.empty())
return std::unordered_set<unsigned>();
return {};
bool odd = max_parity % 2 == 1;
std::unordered_set<unsigned> w1;
std::unordered_set<unsigned> removed;
region_t w1;
strategy_t strategy;
while (!subgame.empty())
{
// Recursion on max_parity.
std::unordered_set<unsigned> u;
attractor(subgame, u, max_parity, odd, true);
// Recursion on max_parity.
region_t u;
auto strat_u = attractor(subgame, u, max_parity, odd, true);
for (unsigned s: u)
subgame.erase(s);
auto w1_ = winning_region(subgame, max_parity - 1);
std::unordered_set<unsigned> w0_;
if (odd && w1_.size() != subgame.size())
std::set_difference(subgame.begin(), subgame.end(),
w1_.begin(), w1_.end(),
std::inserter(w0_, w0_.begin()));
// if !odd, w0_ is not used.
for (unsigned s: u)
subgame.insert(s);
for (unsigned s: u)
subgame.erase(s);
region_t w00; // Even's winning region in the first recursive call.
region_t w10; // Odd's winning region in the first recursive call.
strategy_t s10; // Odd's winning strategy in the first recursive call.
std::tie(w10, s10) = solve_rec(subgame, max_parity - 1);
if (odd && w10.size() != subgame.size())
for (unsigned s: subgame)
if (w10.find(s) == w10.end())
w00.insert(s);
// If !odd, w00 is not used, no need to compute it.
subgame.insert(u.begin(), u.end());
if (odd && w1_.size() + u.size() == subgame.size())
{
for (unsigned s: subgame)
w1.insert(s);
break;
}
else if (!odd && w1_.empty())
break;
if (odd && w10.size() + u.size() == subgame.size())
{
strategy.insert(s10.begin(), s10.end());
strategy.insert(strat_u.begin(), strat_u.end());
w1.insert(subgame.begin(), subgame.end());
return {w1, strategy};
}
else if (!odd && w10.empty())
return {};
// Unrolled tail-recursion on game size.
auto& wni = odd ? w0_ : w1_;
attractor(subgame, wni, max_parity, !odd);
// Recursion on game size.
auto& wni = odd ? w00 : w10;
auto strat_wni = attractor(subgame, wni, max_parity, !odd);
if (!odd)
strat_wni.insert(s10.begin(), s10.end());
for (unsigned s: wni)
{
subgame.erase(s);
removed.insert(s);
}
for (unsigned s: wni)
subgame.erase(s);
if (!odd)
for (unsigned s: wni)
w1.insert(s);
region_t w11; // Odd's winning region in the second recursive call.
strategy_t s11; // Odd's winning strategy in the second recursive call.
std::tie(w11, s11) = solve_rec(subgame, max_parity);
w1.insert(w11.begin(), w11.end());
strategy.insert(s11.begin(), s11.end());
if (!odd)
{
strategy.insert(strat_wni.begin(), strat_wni.end());
w1.insert(wni.begin(), wni.end());
}
for (unsigned s: removed)
subgame.insert(s);
return w1;
subgame.insert(wni.begin(), wni.end());
return {w1, strategy};
}
int reachability_state::compare(const state* other) const
......
......@@ -22,6 +22,7 @@
#include <algorithm>
#include <memory>
#include <ostream>
#include <unordered_map>
#include <vector>
#include <bddx.h>
......@@ -94,8 +95,12 @@ public:
/// Print the parity game in PGSolver's format.
void print(std::ostream& os);
// Compute the winner of this game using Zielonka's recursive algorithm.
// False is Even and True is Odd.
typedef std::unordered_set<unsigned> region_t;
// Map state number to index of the transition to take.
typedef std::unordered_map<unsigned, unsigned> strategy_t;
/// Compute the winning strategy and winning region of this game for player
/// 1 using Zielonka's recursive algorithm.
/** \verbatim
@article{ zielonka.98.tcs
title = "Infinite games on finitely coloured graphs with applications to
......@@ -108,7 +113,7 @@ public:
author = "Wieslaw Zielonka",
}
\endverbatim */
bool winner() const;
std::pair<region_t, strategy_t> solve() const;
/// Whether player 1 has a winning strategy from the initial state.
/// Implements Calude et al.'s quasipolynomial time algorithm.
......@@ -139,17 +144,16 @@ private:
typedef twa_graph::graph_t::edge_storage_t edge_t;
// Compute (in place) a set of states from which player can force a visit
// through set.
// through set, and a strategy to do it.
// if attr_max is true, states that can force a visit through an edge with
// max parity are also counted in.
void attractor(const std::unordered_set<unsigned>& subgame,
std::unordered_set<unsigned>& set, unsigned max_parity,
bool player, bool attr_max = false) const;
// Compute the winning region for player Odd.
std::unordered_set<unsigned>
winning_region(std::unordered_set<unsigned>& subgame,
unsigned max_parity) const;
strategy_t attractor(const region_t& subgame, region_t& set,
unsigned max_parity, bool odd,
bool attr_max = false) const;
// Compute the winning strategy and winning region for player 1.
std::pair<region_t, strategy_t>
solve_rec(region_t& subgame, unsigned max_parity) const;
};
......
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