#14492: Modular group cohomology, version 2.1.4
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Reporter: SimonKing | Owner: tbd
Type: defect | Status: needs_review
Priority: major | Milestone: sage-5.10
Component: packages: optional | Resolution:
Keywords: group cohomology | Work issues:
Report Upstream: N/A | Reviewers:
Authors: SimonKing | Merged in:
Dependencies: | Stopgaps:
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Comment (by SimonKing):
Replying to [comment:21 vbraun]:
> I still get the `from_scratch=True` error, and its completely
reproducible. Installation works fine (and the doctests that actually
perform computations seem to be working, too). I'll attach a more complete
log.
Aha, now I think I understand what is happening!
The output looks as if you did not run the test suite (by `export
SAGE_CHECK=yes` before installing the package), but you did run `sage -t`
on the source files (or on their copies in local/lib/python/site-
packages).
The test suite considers each doc string separately. Hence, it recursively
finds out which modules, classes functions and methods are defined,
extracts the doc of one item after the other, each time writing one doc
string into a temporary file, and running sage -t on this temporary file.
But it is ''not'' supposed to run sage -t on, say,
`pGroupcCohomology/factory.py`.
Reason: The doc tests are supposed to demonstrate how the different sub-
problems of cohomology computations are done. Hence, in the vast majority
of cases, we want a computation from scratch. But if the first test puts a
result into the cache, then the second test might be disturbed.
Example: One test creates the computational set-up for the cohomology of
the `SmallGroup(8,3)` (that's the dihedral group) from scratch, but does
''not'' complete the computation. This test will create an item in the
cache that is only computed out to degree zero. Another test might then
demonstrate that some ''completely'' computed cohomology rings can be
found in the data base, accessible by, say, `CohomologyRing(8,3)`.
However, `CohomologyRing` factory would first try to find the result in
the cache, before accessing the data base on disk or in internet. Hence,
it will return the degree-zero approximation of the ring. Thi explains why
you got
{{{
45 print H0
46 Expected:
47 Cohomology ring of Dihedral group of order 8 with coefficients
in GF(2)
48 <BLANKLINE>
49 Computation complete
50 Minimal list of generators:
51 [c_2_2: 2-Cocycle in H^*(D8; GF(2)),
52 b_1_0: 1-Cocycle in H^*(D8; GF(2)),
53 b_1_1: 1-Cocycle in H^*(D8; GF(2))]
54 Minimal list of algebraic relations:
55 [b_1_0*b_1_1]
56 Got:
57 <BLANKLINE>
58 Cohomology ring of Dihedral group of order 8 with coefficients
in GF(2)
59 <BLANKLINE>
60 Computed up to degree 0
61 Minimal list of generators:
62 []
63 Minimal list of algebraic relations:
64 []
65 <BLANKLINE>
66
}}}
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/14492#comment:22>
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