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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