As Martin said, this is not a bug. However, the error message itself is
slightly vague because it only states partition. We could simply run
sorted(part, reverse=True) before passing it off to create the Partition in
the SetPartitions __classcall__. This would make the behavior less
surprising, and our output does not match the input sizes (since it is lex
based). I think we probably just didn't think about normalizing input here.
Also, I found this bug:
sage: SP = SetPartitions(10, [4,3,2,1])
sage: SP.random_element()
{{1, 2, 4, 5, 7, 8}, {3, 6}, {9}, {10}}
Best,
Travis
On Tuesday, February 15, 2022 at 1:51:32 AM UTC+9 axio...@yahoo.de wrote:
> The argument providing the block sizes is required to be an integer
> partition (or something that sage can make into an integer partition), as
> the error message indicates.
>
> One might argue that Partition (and hence SetPartition) should take lists
> in any order, but this would also increase the likelihood of typos going
> undetected, I guess.
>
> Martin
>
> On Monday, 14 February 2022 at 13:02:39 UTC+1 mitch...@gmail.com wrote:
>
>> Hello,
>>
>> I am currently working with set partitions and I encountered possible bug
>> when creating SetPartitions instance with specified partition sizes:
>>
>> ```
>> sage: SetPartitions(10, [4,3,2,1])
>>
>> Set partitions of {1, 2, 3, 4, 5, 6, 7, 8, 9, 10} with sizes in [4, 3, 2,
>> 1]
>> ```
>>
>> The above works, but changing the order of sizes gives error:
>> ```
>> sage: SetPartitions(10, [1,2,3,4])
>>
>>
>>
>> ---------------------------------------------------------------------------
>> ValueError Traceback (most recent call
>> last)
>> <ipython-input-4-90164a225d10> in <module>
>> ----> 1 SetPartitions(Integer(10),
>> [Integer(1),Integer(2),Integer(3),Integer(4)])
>>
>> /usr/lib/python3/dist-packages/sage/misc/classcall_metaclass.pyx in
>> sage.misc.classcall_metaclass.ClasscallMetaclass.__call__
>> (build/cythonized/sage/misc/classcall_metaclass.c:1714)()
>> 332 """
>> 333 if cls.classcall is not None:
>> --> 334 return cls.classcall(cls, *args, **kwds)
>> 335 else:
>> 336 # Fast version of type.__call__(cls, *args, **kwds)
>>
>> /usr/lib/python3/dist-packages/sage/combinat/set_partition.py in
>> __classcall_private__(cls, s, part)
>> 2025 else:
>> 2026 if part not in Partitions(len(s)):
>> -> 2027 raise ValueError("part must be a partition of
>> %s"%len(s))
>> 2028 else:
>> 2029 return SetPartitions_setparts(s,
>> Partition(part))
>>
>> ValueError: part must be a partition of 10
>> ```
>>
>> Other orders od partition sizes (other than descending) also gives the
>> same error:
>> ```
>> sage: SetPartitions(10, [4,2,3,1])
>> <the same error as above>
>> ```
>>
>> Diferent sets also show this behavior:
>> ```
>> sage: SetPartitions(8, [4,3,1])
>> <OK>
>>
>>
>> ```
>>
>> ```
>> sage: SetPartitions(8, [4,3,1])
>>
>> <Error>
>> ```
>>
>> The same happens when using sage as a module within Python
>>
>> I am using Sage version 9.0, using Python 3.8.10.
>> Operating system is Ubuntu 20.04.3 (64bit)
>>
>> Best regards,
>> Ondra
>>
>
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