#13516: prime_powers doesn't work with start very well
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Reporter: kcrisman | Owner: was
Type: defect | Status: needs_work
Priority: major | Milestone: sage-5.4
Component: number theory | Resolution:
Keywords: beginner | Work issues:
Report Upstream: N/A | Reviewers:
Authors: Kevin Halasz | Merged in:
Dependencies: | Stopgaps:
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Changes (by dimpase):
* status: needs_review => needs_work
Comment:
The comment on line 708 in {{{sage/rings/arith.py}}} needs to be fixed,
too - it talks about primes rather than prime powers.
I also think that the following:
{{{
sage: prime_powers(10,7)
761 Traceback (most recent call last):
762 ...
763 ValueError: the first input must be less than the
second input, however, 10 > 7
}}}
i.e. the corresponding implementation logic is not right, in the sense
that it should just return empty lists rather than throwing exceptions.
And negative {{{start}}} should be allowed too (cf. the semantics of
{{{range()}}}).
Then, in the following fragment
{{{
783 output = prime_range(start,stop)
784 if start == 1:
785 output.append(1)
786
787 s = stop.sqrt()
788 for p in prime_range(stop):
}}}
{{{prime_range()}}}, which is not cheap, is basically called two times
instead of one.
One can do with one call to {{{prime_range(stop)}}} just fine.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/13516#comment:11>
Sage <http://www.sagemath.org>
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