#5107: incorrect trailing digits for continued fraction
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Reporter: robertwb | Owner: somebody
Type: defect | Status: new
Priority: critical | Milestone: sage-4.1.2
Component: basic arithmetic | Keywords:
Reviewer: | Author:
Merged: |
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Comment(by AlexGhitza):
The computation is done in the function {{{continued_fraction_list()}}} of
{{{rings/arith.py}}}, where it says "This may be slow for real number
input, since it's implemented in pure Python. For rational number input
the PARI C library is used."
I wonder why we're not using PARI also when the input is a real number.
It's fast, and it looks right:
{{{
sage: x = sqrt(2)
sage: CFF = ContinuedFractionField()
sage: CFF(pari(x).contfrac().python())
[1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2]
sage: timeit("CFF(pari(x).contfrac().python())
625 loops, best of 3: 258 µs per loop
sage: timeit("CFF(continued_fraction_list(x))")
625 loops, best of 3: 1.17 ms per loop
}}}
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Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/5107#comment:2>
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