#16306: Replace =0 by is_zero() in test for matrix being alternating
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       Reporter:  darij              |        Owner:
           Type:  defect             |       Status:  needs_review
       Priority:  trivial            |    Milestone:  sage-6.2
      Component:  linear algebra     |   Resolution:
       Keywords:                     |    Merged in:
        Authors:  Darij Grinberg     |    Reviewers:
Report Upstream:  N/A                |  Work issues:
         Branch:                     |       Commit:
  public/combinat/matrix0-fix        |  4d4cbe0664c62dce9780d82e8eb948ee420ce521
   Dependencies:                     |     Stopgaps:
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Comment (by darij):

 1) I don't have good examples. We have semirings where 0 is not the zero
 in Sage (try `TropicalSemiring(ZZ)`), but this particular method doesn't
 make much sense for these. This is more an issue of principle: We might
 eventually get rings like Grothendieck's lambda-rings (the ring of power
 series over a given ring K, with multiplication of power series as
 addition, and a weirder multiplication -- and, before you ask, there are
 finite-dimensional quotients of this, so it's not all lazy power series,
 so testing for zeroness does make sense), on which there will suddenly be
 a lot of failing code due to the fact that the coerce of 1 (not the coerce
 of 0) is the zero element.

 2) I don't know. I wouldn't make an assumption on the boolean coerce of a
 ring element. But maybe I could...

--
Ticket URL: <http://trac.sagemath.org/ticket/16306#comment:4>
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