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Fix a case where Coefficients(B,v) returned a list instead of fail although the vector v did not lie in the underlying vector space V of B #5335

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Jan 19, 2023

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resolves #5334

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Up to now it could happen that Coefficients( B, v ) returned a list instead of fail although the vector v did not lie in the underlying vector space V of B.
In these cases, V was a Gaussian row space and the returned list described the coefficients w.r.t. an extension field. In particular, the entries of this list were not contained in LeftActingDomain( V ).

@ThomasBreuer ThomasBreuer added kind: bug: wrong result Issues describing bugs that result in mathematically or otherwise wrong results, and PRs fixing them topic: library release notes: to be added PRs introducing changes that should be (but have not yet been) mentioned in the release notes labels Jan 19, 2023
ThomasBreuer added a commit to ThomasBreuer/gap that referenced this pull request Jan 19, 2023
- Let the filters created by `DeclareHandlingByNiceBasis` imply
  `IsFreeLeftModule`.
  This was the case before the changes from gap-system#3006, and this change fixes
  the problem described in gap-system#5322, as I had sketched in the discussion of gap-system#5325.
- Document this change (following gap-system#5325).
- Increase the rank of `IsHandledByNiceBasis` by 2.
  Then we get back to the rank before the changes from gap-system#3006.
  This way, the `\in` method with second argument in
  `IsFreeLeftModule and IsHandledByNiceBasis` is again ranked higher than
  the one with second argument `IsFreeLeftModule and IsFiniteDimensional`.
  The bug described in issue gap-system#5334 which has been found because of the
  reordering of these two methods (due to gap-system#3006)
  gets fixed via pull request gap-system#5335,
  now we can return to the better method ordering.
  (I do not like uprankings, but I have no better idea to solve this problem.)
@fingolfin fingolfin changed the title fix a bug in Coefficients Fix a case where Coefficients(B,v) returned a list instead of fail although the vector v did not lie in the underlying vector space V of B Jan 19, 2023
@fingolfin fingolfin added release notes: use title For PRs: the title of this PR is suitable for direct use in the release notes and removed release notes: to be added PRs introducing changes that should be (but have not yet been) mentioned in the release notes labels Jan 19, 2023
@fingolfin fingolfin merged commit 1f90b51 into gap-system:master Jan 19, 2023
fingolfin pushed a commit that referenced this pull request Jan 19, 2023
- Let the filters created by `DeclareHandlingByNiceBasis` imply
  `IsFreeLeftModule`.
  This was the case before the changes from #3006, and this change fixes
  the problem described in #5322, as I had sketched in the discussion of #5325.
- Document this change (following #5325).
- Increase the rank of `IsHandledByNiceBasis` by 2.
  Then we get back to the rank before the changes from #3006.
  This way, the `\in` method with second argument in
  `IsFreeLeftModule and IsHandledByNiceBasis` is again ranked higher than
  the one with second argument `IsFreeLeftModule and IsFiniteDimensional`.
  The bug described in issue #5334 which has been found because of the
  reordering of these two methods (due to #3006)
  gets fixed via pull request #5335,
  now we can return to the better method ordering.
  (I do not like uprankings, but I have no better idea to solve this problem.)
@ThomasBreuer ThomasBreuer deleted the TB_coefficients branch January 20, 2023 08:20
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Regression: recent changes caused package guava to fail its test suite
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