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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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5
NEWS
View file

@ -24,6 +24,11 @@ New in spot 2.7.2.dev (not yet released)
acc_cond::acc_code::top_conjuncts() can be used to split an
acceptance condition on the top-level & or |.
- minimize_obligation() learned to work on very weak automata even
if the formula or negated automaton are not supplied. (This
allows "autfilt [-D] --small" to minimize very-weak automata
whenever they are found to represent obligation properties.)
Bugs fixed:
- When processing CSV files with MSDOS-style \r\n line endings,

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;
}
}

13
tests/core/optba.test
View file

@ -1,6 +1,6 @@
#!/bin/sh
# -*- coding: utf-8 -*-
# Copyright (C) 2015, 2017 Laboratoire de Recherche et Développement
# Copyright (C) 2015, 2017, 2019 Laboratoire de Recherche et Développement
# de l'Epita (LRDE).
#
# This file is part of Spot, a model checking library.
@ -160,3 +160,14 @@ test `autfilt --exclusive-ap=c1,c2 --high --small --stats=%s input` = 18
# But we should have 19 with Büchi acceptance, not 20.
test `autfilt --exclusive-ap=c1,c2 --high --small -B --stats=%s input` = 19
# This should be reduced to a 3-state minimal WDBA if we
# correctly recognize that this is an obligation. Issue #379.
cat >in <<EOF
HOA: v1 Start: 0 States: 4 Acceptance: 1 Inf(0)
AP: 2 "v0" "v1" --BODY-- State: 0 "T3_init" [t] 0 [!0 & !1] 1
State: 1 "T2" [0&1] 1 [0&1] 2 [!0&!1] 2 [0&1] 3 [!0&!1] 1
State: 2 "T1" {0} [0&1] 2 State: 3 "all" {0} [t] 3 --END--
EOF
test '3,6' = `autfilt --small in --stats=%s,%e`