1b81ecb80c
Based on a report by Emmanuel Filiot, who was surprized that dualizing Büchi did not always produce co-Büchi. * spot/twaalgos/dualize.cc: Remove the call to cleanup_acceptance_here. * spot/twaalgos/dualize.hh: Improve documentation. * NEWS: Mention the possible backward incompatible change. * tests/core/dualize.test, tests/python/dualize.py, tests/python/pdegen.py: Adjust test cases. * spot/twaalgos/complement.cc (complement): Call cleanup_acceptance_here when dualize() returns a smaller automaton. * THANKS: Add Emmanuel.
75 lines
3.4 KiB
C++
75 lines
3.4 KiB
C++
// -*- coding: utf-8 -*-
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// Copyright (C) by the Spot authors, see the AUTHORS file for details.
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//
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// This file is part of Spot, a model checking library.
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//
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// Spot is free software; you can redistribute it and/or modify it
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// under the terms of the GNU General Public License as published by
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// the Free Software Foundation; either version 3 of the License, or
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// (at your option) any later version.
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//
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// Spot is distributed in the hope that it will be useful, but WITHOUT
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// ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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// or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public
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// License for more details.
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//
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// You should have received a copy of the GNU General Public License
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// along with this program. If not, see <http://www.gnu.org/licenses/>.
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#pragma once
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#include <spot/misc/common.hh>
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#include <spot/twa/fwd.hh>
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namespace spot
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{
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/// \ingroup twa_misc
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/// \brief Complement an automaton by dualizing it.
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///
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/// Given an automaton \a aut of any type, produces the dual as
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/// output. Before dualization, the automaton will be completed if
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/// it isn't already, but any sink state in the output might then be
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/// removed.
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///
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/// Dualizing the automaton is done by interpreting the outgoing
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/// transitions of a state as a Boolean function, and then swapping
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/// operators ∧ and ̇∨. This first step does not have to be done on
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/// deterministic automata. Additionally, the acceptance condition
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/// is dualized by swapping operators ∧ and ̇∨, and swapping Inf and
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/// Fin.
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///
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/// For instance, the dual of a generalized Büchi automaton will be
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/// a generalized co-Büchi automaton.
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///
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/// If the input acceptance condition accepts every infinite path
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/// (such as "t" or "Inf(0)|Fin(0)") and the automaton is not
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/// complete, then the input automaton will be assumed to have Büchi
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/// acceptance in order to complete it, and the output will then
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/// have co-Büchi acceptance.
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///
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/// Due to a defect in the way transition-based alternating automata
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/// are represented in Spot and in the HOA format, existential
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/// automata with transition-based acceptance will be converted to
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/// use state-based acceptance before dualization. See
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/// https://github.com/adl/hoaf/issues/68 for more information.
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///
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/// If the input automaton is deterministic, the output will be deterministic.
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/// If the input automaton is existential, the output will be universal.
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/// If the input automaton is universal, the output will be existential.
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/// Finally, if the input automaton is alternating, the result is alternating.
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/// More can be found on page 22 (Definition 1.6) of \cite loding.98.msc .
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///
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/// Functions like to_generalized_buchi() or remove_fin() are frequently
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/// called on existential automata after dualize() to obtain an easier
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/// acceptance condition, but maybe at the cost of losing determinism.
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///
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/// Up to version 2.11.6, this function used to call
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/// cleanup_acceptance_here() to simplify the acceptance condition
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/// after dualization. This caused some surprizes, users expected
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/// the dual of a Büchi automaton to be a co-Büchi automaton, but
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/// cleanup_acceptance_here() sometimes reduced the condition to `t`
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/// when all states where accepting. This function is not called
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/// anymore since version 2.12.
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SPOT_API twa_graph_ptr
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dualize(const const_twa_graph_ptr& aut);
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}
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