#16198: replace default algorithm for log(power series)
-------------------------+-------------------------------------------------
Reporter: rws | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-6.2
Component: calculus | Keywords: log, function, series
Merged in: | expansion
Reviewers: | Authors:
Work issues: | Report Upstream: N/A
Commit: | Branch:
Stopgaps: | Dependencies:
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The default method for `log(power series)` is from GiNAC but it fails when
the constant coefficient is not 1:
{{{
sage: R.<x> = PowerSeriesRing(ZZ)
sage: log(2-x)
---------------------------------------------------------------------------
ArithmeticError Traceback (most recent call
last)
<ipython-input-45-e3dfbfa60870> in <module>()
----> 1 log(Integer(2)-x)
/home/ralf/sage/local/lib/python2.7/site-packages/sage/functions/log.pyc
in __call__(self, *args, **kwds)
338 if base is None:
339 if len(args) == 1:
--> 340 return GinacFunction.__call__(self, *args, **kwds)
341 # second argument is base
342 base = args[1]
/home/ralf/sage/local/lib/python2.7/site-
packages/sage/symbolic/function.so in
sage.symbolic.function.BuiltinFunction.__call__
(sage/symbolic/function.cpp:8750)()
/home/ralf/sage/local/lib/python2.7/site-
packages/sage/rings/power_series_ring_element.so in
sage.rings.power_series_ring_element.PowerSeries.log
(sage/rings/power_series_ring_element.c:12985)()
ArithmeticError: constant term of power series is not 1
}}}
Pari has no problems:
{{{
? log(2-x)
%1 = 0.69314718055994530941723212145817656807 - 1/2*x - 1/8*x^2 - 1/24*x^3
- 1/64*x^4 - 1/160*x^5 - 1/384*x^6 - 1/896*x^7 - 1/2048*x^8 - 1/4608*x^9 -
1/10240*x^10 - 1/22528*x^11 - 1/49152*x^12 - 1/106496*x^13 - 1/229376*x^14
- 1/491520*x^15 + O(x^16)
}}}
so calling Pari should be made default in `PowerSeries.log()`.
--
Ticket URL: <http://trac.sagemath.org/ticket/16198>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
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