Commit 1e52d2a7 authored by Alexandre Duret-Lutz's avatar Alexandre Duret-Lutz

doc: more doc about determinization

* doc/org/autfilt.org: Here.
parent 0288aaa3
......@@ -204,7 +204,7 @@ autfilt --help | sed -n '/Output automaton type:/,/^$/p' | sed '1d;$d'
#+RESULTS:
: -B, --ba Büchi Automaton (with state-based acceptance)
: -C, --complete output a complete automaton
: --generic any acceptance is allowed (default)
: -G, --generic any acceptance is allowed (default)
: -M, --monitor Monitor (accepts all finite prefixes of the given
: property)
: -S, --state-based-acceptance, --sbacc
......@@ -240,8 +240,49 @@ defaults to =--high= (unless specified otherwise). If a simplification
level is given without specifying any goal, then the goal default to =--small=.
So if you want to reduce the size of the automaton, try =--small= and
if you want to try to make (or keep) it deterministic (there is to
guaranty of result, this is only a preference) try =--deterministic=.
if you want to try to make (or keep) it deterministic use
=--deterministic=.
Note that the =--deterministic= flag has two possible behaviors
depending on the constraints on the acceptance conditions:
- When =autfilt= is configured to work with generic acceptance (the
=--generic= option, which is the default), then the
=--deterministic= flag will do whatever it takes to output a
deterministic automaton, and this includes changing the acceptance
condition if needed (see below).
- If options =--tgba= or =--ba= are used, the =--deterministic= option
is taken as a /preference/: =autfilt= will try to favor determinism
in the output, but it may not always succeed and may output
non-deterministic automata. Note that if =autfilt --deterministic
--tgba= fails to output a deterministic automaton, it does not
necessarily implies that a deterministic TGBA does not exist: it
just implies that =autfilt= could not find it.
** Determinization
Spot has basically two ways to determinize automata, and that it uses
when =--deterministic= is passed.
- Automata that express obligation properties (this can be decided),
can be *determinized and minimized* into weak Büchi automata, as
discussed by [[http://www.daxc.de/eth/paper/atva07.pdf][Dax at al. (ATVA'07)]].
- Büchi automata (preferably with transition-based acceptance) can be
determinized into parity automata using a Safra-like procedure close
to the one presented by [[http://www.romanredz.se/papers/FI2012.pdf][Redziejowski (Fund. Inform. 119)]], with a few
additional tricks. This procedure does not necessarily produce a
minimal automaton.
When =--deterministic= is used, the first of these two procedures is
attempted on any supplied automaton. (It's even attempted for
deterministic automata, because that might reduce them.)
If that first procedure failed, and the input automaton is not
deterministic and =--generic= (the default for =autfilt=) is used,
then the second procedure is used. In this case, automata will be
first converted to transition-based Büchi automata if their condition
is more complex.
* Transformations
......
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