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Fun with the new Logic module

The logic module is slowly becoming useful. This week I managed to get some basic inference in propositional logic working. This should be enough for the assumption sysmtem (although having first-order inference would be cool).

You can pull from my branch:

git pull http://fseoane.net/git/sympy.git logic

Here are some examples of what it can do:

First, importing and defining our symbols

In [1]: A, B, C = symbols('ABC')
In [2]: from sympy.logic import *

It works with Symbols just as you would expect

In [3]: And(A, B)
Out[3]: And(A, B)

It applies De Morgan Rules automatically

In [4]: Not(Or(A, B))
Out[4]: And(Not(A), Not(B))

converts to conjuntive normal form (CNF)

In [5]: to_cnf(Implies(A, And(B, C)))
Out[5]: And(Or(B, Not(A)), Or(C, Not(A)))

Some basic inference:

In [6]: pl_true( Or(A, B), {A : True})  # what can we say about Or(A, B) if A is True ?
Out[6]: True

In [7]: pl_true ( And(A, B), {B: False}) # what is And(A, B) if B is False
Out[7]: False

To be discussed:
- I’m not sure if we should override &&, || on Symbol so that we can do A && B instead of And(A, B). If would make the code
cleaner, but also I don’t want to bloat Symbol any more. What do you think ?

I’m very proud of this in the sense that it is a nice clean module that will hopefully serve as the foundation of the new assumption
system.

This entry was posted on Sunday, May 31st, 2009 at 11:16 pm and is filed under sympy, Tecnologí­a. You can follow any responses to this entry through the RSS 2.0 feed. You can skip to the end and leave a response. Pinging is currently not allowed.

4 Responses to “Fun with the new Logic module”

  1. Ondrej Certik Says:
    May 31st, 2009 at 11:31 pm

    I got this warning:

    In [7]: to_cnf(Implies(A, And(B, C)))
    sympy/logic/boolalg.py:93: DeprecationWarning: object.__init__() takes no parameters
    return super(BooleanFunction, self).__init__(*args, **kwargs)
    Out[7]: And(Or(B, Not(A)), Or(C, Not(A)))

    otherwise it works fine, the following tests failed:

    _______________ sympy/logic/tests/test_boolalg.py:test_And_bool ________________
    File “/home/ondrej/repos/sympy/sympy/logic/tests/test_boolalg.py”, line 14, in test_And_bool
    assert And(True, True ) == True
    AssertionError
    ________________________________________________________________________________
    ________________ sympy/logic/tests/test_boolalg.py:test_Or_bool ________________
    File “/home/ondrej/repos/sympy/sympy/logic/tests/test_boolalg.py”, line 19, in test_Or_bool
    assert Or(True, True ) == True
    AssertionError
    ________________________________________________________________________________
    _______________ sympy/logic/tests/test_boolalg.py:test_Not_bool ________________
    File “/home/ondrej/repos/sympy/sympy/logic/tests/test_boolalg.py”, line 24, in test_Not_bool
    assert Not(True, True ) == [False, False]
    AssertionError

    tests finished: 1458 passed, 4 failed, 4 skipped, 28 xfailed, 1 xpassed in 100.06 seconds

    and 5 doctests failed, just run:

    $ bin/doctest
    […]
    ====== tests finished: 209 passed, 4 failed, 1 exceptions in 2.48 seconds ======
    DO *NOT* COMMIT!

  2. Ondrej Certik Says:
    May 31st, 2009 at 11:37 pm

    As to overriding || and &&, I think we should and it should be overridden in the Basic class.

  3. Zeroth Says:
    June 17th, 2009 at 4:47 pm

    Why don’t you override the operators for and, or, etc, so you could use the python keywords? I believe they are here: http://docs.python.org/reference/datamodel.html#emulating-numeric-types

  4. fabian Says:
    June 19th, 2009 at 12:20 pm

    Yes, that is done now

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