Hi Travis,
>From my point of view, this can only be considered a bug: extremely
surprising behaviour leading to subtle problems in user code (my code).
Possibly, the bug is higher up than FiniteEnumeratedSets, though.
I'll explain: This came about when using Subsets. Basically, I'm doing
something like:
for S in Subsets(GF(13).list(), 5):
if sum(S) == 1:
print "Monkey"
This code works as expected and prints monkeys galore when evaluating it
in a Sage shell. Now restart Sage and call the following line before
calling the above snippet:
a = list(Subsets(range(13), 5))
And suddenly the first code snippet will never print anything.
Tell me that's not a bug!
Best,
Johan
Travis Scrimshaw writes:
> Hey Johan,
> The problem is that we want finite enumerated sets to be hashable,
> picklable, and unique as they get used as keys for CombinatorialFreeModule,
> among other things, and it is implemented using UniqueRepresentation. The
> problem is that 1 = 1 with the same hash value whether in ZZ or GF(97), so
> the enumerated set is the same. However, I would not regard this as a bug,
> but a "feature" of the unique behavior and the coercion framework.
>
> My guess is that you are treating the finite enumerated set as a tuple,
> and so I would suggest that you just used tuples (which has far less
> overhead).
>
> Best,
> Travis
>
>
> On Wednesday, November 2, 2016 at 12:45:21 PM UTC-5, Johan S. H. Rosenkilde
> wrote:
>>
>> Hi all,
>>
>> I just tracked down a nasty bug completely messing up my experiments to
>> this internal caching mechanism. In a clean Sage type:
>>
>> sage: E = FiniteEnumeratedSet([ GF(97)(i) for i in [1,2,3,4,5,6]])
>> sage: type(E[0])
>> <type 'sage.rings.finite_rings.integer_mod.IntegerMod_int'>
>>
>> Restart Sage and type instead
>>
>> sage: E = FiniteEnumeratedSet([1,2,3,4,5,6])
>> sage: type(E[0])
>> <type 'sage.rings.integer.Integer'>
>> sage: E = FiniteEnumeratedSet([ GF(97)(i) for i in [1,2,3,4,5,6]]);
>> type(E[0])
>> <type 'sage.rings.integer.Integer'>
>>
>> Many variations of this theme seem possible.
>>
>> This was Sage 7.5.beta0.
>>
>> Someone knowledgeable can help find the cause and possible other places
>> the bug could appear?
>>
>> Best,
>> Johan
>>
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