#16836: __neg__ fails in CartesianProduct of CombinatorialFreeModule
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Reporter: | Owner:
cnassau | Status: needs_work
Type: | Milestone: sage-6.4
defect | Resolution:
Priority: major | Merged in:
Component: | Reviewers:
categories | Work issues:
Keywords: | Commit:
Authors: | 27861148fe1ec16070603023e9a9fb643f9d6698
Christian Nassau | Stopgaps:
Report Upstream: N/A |
Branch: |
u/cnassau/16836.2 |
Dependencies: |
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Comment (by cnassau):
Replying to [comment:5 vdelecroix]:
> Could you change
> {{{
> sage: F = CombinatorialFreeModule(ZZ, ['a','b'])
> sage: FF = cartesian_product((F,F))
> sage: -FF.an_element() # random - only test that negative can be taken
> }}}
> to something explicit like
> {{{
> sage: F = CombinatorialFreeModule(ZZ, ['a','b'])
> sage: a,b = F.gens()
> sage: c = cartesian_product([a,b-2*a]) + cartesian_product([a,a])
> sage: c
> 2*B[(0, 'a')] - B[(1, 'a')] + B[(1, 'b')]
> sage: FF = cartesian_product((F,F))
> sage: c.parent() == FF
> True
> sage: -c
> -2*B[(0, 'a')] + B[(1, 'a')] - B[(1, 'b')]
> }}}
I have followed these suggestions; the doctest is now more explicit.
> IMHO, the following fails but should work
> {{{
> sage: FF([a,b])
> Traceback (most recent call last)
> ...
>
> TypeError: do not know how to make x (= [B['a'], B['b']])
> an element of self (=Free module generated by {'a', 'b'} over Integer
Ring
> (+) Free module generated by {'a', 'b'} over Integer Ring)
> }}}
I agree that this looks like a reasonable expectation, but I'm afraid that
this might be a bit contentious since it would involve changes in the
combinatorial heartland. I'd prefer to keep such matters out of this
ticket which is essentially just a simple bugfix.
Thanks for taking the time to look into this ticket!
Cheers,
Christian
--
Ticket URL: <http://trac.sagemath.org/ticket/16836#comment:7>
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