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minimize_obligation: complement very weak automata if needed

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Fixes #379.

* spot/twaalgos/minimize.cc: Here.
* tests/core/optba.test: Add test case provided by Rüdiger Ehlers.
* NEWS: Mention the improvement.
This commit is contained in:
Alexandre Duret-Lutz 2019-03-20 22:02:02 +01:00
parent ef106e2860
commit 01edf4f8e1
3 changed files with 32 additions and 5 deletions
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19
spot/twaalgos/minimize.cc
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@ -1,5 +1,5 @@
// -*- coding: utf-8 -*-
// Copyright (C) 2010-2018 Laboratoire de Recherche et Développement
// Copyright (C) 2010-2019 Laboratoire de Recherche et Développement
// de l'Epita (LRDE).
//
// This file is part of Spot, a model checking library.
@ -45,6 +45,7 @@
#include <spot/twaalgos/isdet.hh>
#include <spot/twaalgos/dualize.hh>
#include <spot/twaalgos/remfin.hh>
#include <spot/twaalgos/alternation.hh>
#include <spot/tl/hierarchy.hh>
namespace spot
@ -570,8 +571,12 @@ namespace spot
("minimize_obligation() does not support alternation");
// FIXME: We should build scc_info once, pass it to minimize_wdba
// and reuse it for is_terminal_automaton(), and
// is_weak_automaton().
// and reuse it for is_terminal_automaton(),
// is_weak_automaton(), and is_very_weak_automaton().
// FIXME: we should postpone the call to minimize_wdba() until
// we know for sure that we can verify (or that we do not need
// to verify) its output, rather than computing in cases where
// we may discard it.
auto min_aut_f = minimize_wdba(aut_f);
if (reject_bigger)
@ -614,9 +619,15 @@ namespace spot
// Remove useless SCCs.
aut_neg_f = scc_filter(aut_neg_f, true);
}
else if (is_very_weak_automaton(aut_f))
{
// Very weak automata are easy to complement.
aut_neg_f = remove_alternation(dualize(aut_f));
}
else
{
// Otherwise, we cannot check if the minimization is safe.
// Otherwise, we don't try to complement the automaton and
// therefore we cannot check if the minimization is safe.
return nullptr;
}
}