Vector equality coercion problems

[sagetrac-jbmohler]

I think this bit of code should not produce an exception. The vectors should both be coerced to belong to Z8!^3 and compared.

sage: Z8=IntegerModRing(8)
sage: vector(ZZ,[1,2,11])==vector(Z8,[1,2,3])
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
...
AttributeError: 'FreeModule_ambient' object has no attribute 'ambient_vector_space'

Note that a similar thing seems to work in other cases (because 7 is prime and Z7 is a field?).

sage: Z7=IntegerModRing(7)
sage: vector(ZZ,[1,2,10])==vector(Z7,[1,2,3])
True

This may or may not be related, but combining QQ and Z7 produces some wrong results:

sage: Z7=IntegerModRing(7)
sage: vector(Z7,[1,2,3])==vector(QQ,[1,2,3])
False

That those vectors are not equal is truly disturbing. This should either raise an exception about not having compatible parents or should be True. I'll let the coercion guru's argue about that. :)

Component: algebra

Author: Robert Bradshaw

Reviewer: Mike Hansen

Merged: sage-4.3.1.rc1

Issue created by migration from https://trac.sagemath.org/ticket/3638

[robertwb]

comment:2

Attachment: 3638-free-module-coerce.patch.gz

Fixed the Z/8Z case. As for Z/7Z and Q, they are incomparable, which by convention means == returns False. (If it gave an error,we would have to re-think nonsense like "some string" != random_matrix(ZZ, 3) returning False).

[mwhansen]

comment:3

Looks good to me.

[mwhansen]

Author: Robert Bradshaw

[mwhansen]

Reviewer: Mike Hansen

[rlmill]

Merged: sage-4.3.1.rc1