#15144: Binary recurrence sequences
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Reporter: ivogt161 | Owner:
Type: enhancement | Status: new
Priority: minor | Milestone: sage-5.13
Component: number theory | Resolution:
Keywords: | Merged in:
Authors: Isabel Vogt | Reviewers: Eric Larson
Report Upstream: N/A | Work issues:
Branch: | Commit:
Dependencies: | Stopgaps:
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Comment (by elarson3):
'''Issues with code:'''
1. The is_arithmetic function is broken:
{{{
sage: S = BinaryRecurrenceSequence(1,1,1,2)
sage: S.is_arithmetic()
True
sage: [S(i) for i in xrange(10)]
[1, 2, 3, 5, 8, 13, 21, 34, 55, 89]
}}}
2. The period function is broken too:
{{{
sage: S = BinaryRecurrenceSequence(2, -1)
sage: S.period(9)
9
sage: S.period(3)
1
sage: S = BinaryRecurrenceSequence(2, -1) # but re-initialize to clear
cache, and we get the right answer...
sage: S.period(3)
3
}}}
3. The pthpowers function performs sub-optimally when Bound is small
compared to p.
'''Issues with documentation:'''
1. References don't print in the PDF manual.
2. In the BinaryRecurrenceSequence class, order of input listed in
documentation does not match order of input expected by __init__. Also,
missing underscores on u0 and u1 cause funny PDF output.
3. In is_degenerate, the documentation claims u_n = au_{n-1} - bu_{n+1},
which is wrong. Also, please insert a comment saying what aa and bb are;
and also a remark that \alpha, \beta are (b \pm A)/2. Again, missing
underscores on u0 and u1 cause funny PDF output.
4. In is_geometric, the documentation says u_n = a * u_{n-1} or u_n = b *
u_{n-2}, but this isn't what the code checks. Also "sage: S =
BinaryRecurrenceSequence(2,0,1,2)" is written twice.
5. In is_quasigeometric, there are missing backslashese before alpha and
beta. Also, throughout the file, quasigeomtric is sometimes spelled
quadigeomtric.
6. In period function, there is only one - after ``m`` in INPUT section,
which causes funny output in PDF documentation.
6. In pthpowers function, "check" should be "checked", and "U_n" should be
"u_n". Also, comments claim the code continues after 5 rounds of
increasing modulus, but the code checks if it increased 7 times?
7. _is_p_power_mod function: e confused with 3 in 3rd comment.
--
Ticket URL: <http://trac.sagemath.org/ticket/15144#comment:2>
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