twaalgos: introduce match_states(a,b)

This is a useful part for issue #591.

* spot/twaalgos/matchstates.cc, spot/twaalgos/matchstates.hh: New
files.
* spot/twaalgos/Makefile.am: Add them.
* python/spot/impl.i: Add python bindings.
* tests/python/matchstates.py: New file.
* tests/Makefile.am: Add it.
* NEWS: Mention this new function.

spot/twaalgos/Makefile.am

@@ -64,6 +64,7 @@ twaalgos_HEADERS = \
   ltl2tgba_fm.hh \
   magic.hh \
   mask.hh \
+  matchstates.hh \
   minimize.hh \
   mealy_machine.hh \
   couvreurnew.hh \
@@ -139,6 +140,7 @@ libtwaalgos_la_SOURCES = \
   ltl2tgba_fm.cc \
   magic.cc \
   mask.cc \
+  matchstates.cc \
   minimize.cc \
   mealy_machine.cc \
   couvreurnew.cc \

spot/twaalgos/matchstates.cc

@@ -0,0 +1,50 @@
+// -*- coding: utf-8 -*-
+// Copyright (C) by the Spot authors, see the AUTHORS file for details.
+//
+// This file is part of Spot, a model checking library.
+//
+// Spot is free software; you can redistribute it and/or modify it
+// under the terms of the GNU General Public License as published by
+// the Free Software Foundation; either version 3 of the License, or
+// (at your option) any later version.
+//
+// Spot is distributed in the hope that it will be useful, but WITHOUT
+// ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+// or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public
+// License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+#include "config.h"
+#include <spot/twaalgos/matchstates.hh>
+#include <spot/twaalgos/sccinfo.hh>
+#include <spot/twaalgos/product.hh>
+
+namespace spot
+{
+  std::vector<std::vector<unsigned>>
+  match_states(const const_twa_graph_ptr& aut1,
+               const const_twa_graph_ptr& aut2)
+  {
+    twa_graph_ptr prod = product(aut1, aut2);
+    product_states* ps = prod->get_named_prop<product_states>("product-states");
+    if (!ps)
+      return {};
+    scc_info si(prod, scc_info_options::TRACK_SUCCS);
+
+    std::vector<std::vector<unsigned>> v(aut1->num_states());
+    unsigned sz = ps->size();
+    assert(sz == prod->num_states());
+    for (unsigned sp = 0; sp < sz; ++sp)
+      if (si.is_useful_state(sp))
+        {
+          auto [sl, sr] = (*ps)[sp];
+          v[sl].push_back(sr);
+        }
+    return v;
+  }
+
+
+
+}

spot/twaalgos/matchstates.hh

@@ -0,0 +1,40 @@
+// -*- coding: utf-8 -*-
+// Copyright (C) by the Spot authors, see the AUTHORS file for details.
+//
+// This file is part of Spot, a model checking library.
+//
+// Spot is free software; you can redistribute it and/or modify it
+// under the terms of the GNU General Public License as published by
+// the Free Software Foundation; either version 3 of the License, or
+// (at your option) any later version.
+//
+// Spot is distributed in the hope that it will be useful, but WITHOUT
+// ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+// or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public
+// License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+#pragma once
+
+#include <spot/misc/common.hh>
+#include <spot/twa/fwd.hh>
+#include <vector>
+
+namespace spot
+{
+  /// \ingroup twa_algorithms
+  /// \brief match the state of \a aut1 with the states of \a aut2.
+  ///
+  /// Return a vector `V` such that for each state `x` of
+  /// \a aut1, `V[x]` contains the set of states `y` such that
+  /// `(x,y)` is a useful state of `product(aut1,aut2)`.
+  ///
+  /// In particular, if the language of \a aut2 includes the language
+  /// of \a aut1, then any word accepted from state `x` in \a aut1
+  /// is also accepted from one of the states in `V[x]`.
+  SPOT_API std::vector<std::vector<unsigned>>
+  match_states(const const_twa_graph_ptr& aut1,
+               const const_twa_graph_ptr& aut2);
+}