Le mercredi 19 novembre 2014 16:31:35 UTC+1, Jakob Kroeker a écrit :
>
> kcrisman:
>
>
>> It is similar to how our Booleans on expression comparisons return False
>> if we can't prove True
>>
>
>
> Could the usage of a sort of Tristate/multistate implementation kill that
> universe of worms?
> (With the following design: Tristate only comparable to Tristate objects)
>
That's opening another (large) can of worms... ('bout the size of an oil
barrel...) : this <http://en.wikipedia.org/wiki/%C5%81ukasiewicz_logic>
might give you an estimate of the size of the problem. Furthermore, use of
that extension would have pervasive effects in the whole of Sage.For
example, what should do a function expecting either True or False when
getting an hypothetical Unknown ? One might map (coerce) the Tristate
Unknown to False and get the same behaviour, but wouldn't this defeat the
very purpose of adding Tristate ? Furthermore, most of Sage has been
written with the assumption "not(not(X))==X", which no longer holds...
BTW, Maxima has this kind of logic (for example, "is" can return "true",
"false" or "unknown") and uses it, so it's at least conceptually doable.
And useful ! But with very deep consequences.
Shouldn't this be discussed on sage-devel ?
HTH,
--
Emmanuel Charpentier
>
> Jakob
>
>
>
> Am Mittwoch, 19. November 2014 16:16:44 UTC+1 schrieb kcrisman:
>>
>> So you can assume that an empty list means only that sage's algorithms
>>>> find no solution.
>>>>
>>>
>>> I just looked at the documentation of solve and could not find an
>>> explicit statement about missed solutions.
>>>
>>> Even if it is expectable that in some cases (which?) solve may not
>>> return all solutions, it should be explicitly pointed out;
>>> Especially it should be stated that an empty list does not necessarily
>>> imply there are no solutions.
>>>
>>> Other opinions? If everybody agrees, I will open a ticket.
>>>
>>
>> Updating the documentation of both solve? and x.solve? to make it clear
>> that this is the case would be very helpful. It is similar to how our
>> Booleans on expression comparisons return False if we can't prove True.
>>
>
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