#16198: replace default algorithm for log(power series)
-------------------------------------------------+-------------------------
Reporter: rws | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-6.2
Component: calculus | Resolution:
Keywords: log, function, series | Merged in:
expansion | Reviewers:
Authors: | Work issues:
Report Upstream: N/A | Commit:
Branch: | Stopgaps:
Dependencies: |
-------------------------------------------------+-------------------------
Comment (by kcrisman):
I don't think Ginac is actually involved. Take a look at the last piece
of the traceback, which points to
[http://git.sagemath.org/sage.git/tree/src/sage/rings/power_series_ring_element.pyx#n1585
here]. In particular, in sage/rings/power_series_ring_element.pyx,
{{{
if prec is None:
prec = self._parent.default_prec()
if not self[0].is_one():
raise ArithmeticError("constant term of power series is not
1")
zero = self.parent().zero()
t = zero.solve_linear_de(prec,b=self.derivative()/self,f0=0)
return t
}}}
So this is actually hard-coded in for some reason, referring eventually to
`_solve_linear_de` which was factored out of this stuff a very long time
ago.
It could be worth asking around why/whether this is really necessary. I
don't know that I want the above instead of
{{{
sage: log(2-x)
log(-x + 2)
sage: _.taylor(x,0,16)
-1/1048576*x^16 - 1/491520*x^15 - 1/229376*x^14 - 1/106496*x^13 -
1/49152*x^12 - 1/22528*x^11 - 1/10240*x^10 - 1/4608*x^9 - 1/2048*x^8 -
1/896*x^7 - 1/384*x^6 - 1/160*x^5 - 1/64*x^4 - 1/24*x^3 - 1/8*x^2 - 1/2*x
+ log(2)
}}}
note the `log(2)` instead of an approximation.
--
Ticket URL: <http://trac.sagemath.org/ticket/16198#comment:1>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
--
You received this message because you are subscribed to the Google Groups
"sage-trac" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
To post to this group, send email to [email protected].
Visit this group at http://groups.google.com/group/sage-trac.
For more options, visit https://groups.google.com/d/optout.
