#20919: Wrong behaviour when `existence=True` for `incomplete_orthogonal_array`
and
`difference_family`
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Reporter: eviatarbach | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-7.3
Component: combinatorial designs | Resolution:
Keywords: days78 | Merged in:
Authors: | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
Dependencies: | Stopgaps:
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Description changed by eviatarbach:
Old description:
> The docstring for `designs.incomplete_orthogonal_array` claims that if
> `existence=True`, the function will return a boolean or `Unknown`.
> However, for certain values, it returns the array.
>
> For example,
>
> {{{
> sage: type(designs.incomplete_orthogonal_array(9,82,[9],existence=True))
> <type 'list'>
> }}}
>
> I encountered this while working on something else, and I have no idea of
> the math behind this, but it seems to be incorrect. The problem seems to
> be in the block starting at line 1371 in `orthogonal_arrays.py` ("From a
> quasi-difference matrix"); all other branches in the function take into
> account whether `existence` is set, but this one does not.
New description:
The docstring for `designs.incomplete_orthogonal_array` claims that if
`existence=True`, the function will return a boolean or `Unknown`.
However, for certain values, it returns the array.
For example,
{{{
sage: type(designs.incomplete_orthogonal_array(9,82,[9],existence=True))
<type 'list'>
}}}
I encountered this while working on something else, and I have no idea of
the math behind this, but it seems to be incorrect. The problem seems to
be in the block starting at line 1371 in `orthogonal_arrays.py` ("From a
quasi-difference matrix"); all other branches in the function take into
account whether `existence` is set, but this one does not.
Similarly,
{{{
sage: type(designs.difference_family(3, 2, 1, existence=True)[0])
<class
'sage.rings.finite_rings.integer_mod_ring.IntegerModRing_generic_with_category'>
}}}
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Ticket URL: <https://trac.sagemath.org/ticket/20919#comment:3>
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