Hi Ondrej,
I burrowed into the source code and the problem seems to be caused by
the pattern matching
in the `sympy/core/power.py` file. It expects a term of the form
k*x**l, but if there
are two terms of the same power in x it won't match. This gives l=0
and the
following while loop doesn't terminate.
term2 = rest.as_leading_term(x)
k, l = Wild("k"), Wild("l")
r = term2.match(k*x**l)
k, l = r[k], r[l]
...
while l * m < n:
A naive fix is attached below following, which seems to work, I'm not
sure what it's limitations are.
I think checking l>0 is a good thing though...
Andrew
--- sympy/core/power.py 2009-03-12 07:41:25.000000000 +1100
+++ power.py 2009-03-24 12:17:35.000000000 +1100
@@ -534,13 +534,15 @@
n2 = getn(rest)
if n2 is not None:
n = n2
- term2 = rest.as_leading_term(x)
+
+ from sympy import collect
+ term2 = collect(rest.as_leading_term(x),x)
k, l = Wild("k"), Wild("l")
r = term2.match(k*x**l)
k, l = r[k], r[l]
- if l.is_Integer:
+ if l.is_Integer and l>0:
l = int(l)
- elif l.is_number:
+ elif l.is_number and l>0:
l = float(l)
else:
raise Exception("Not implemented")
On Mar 20, 2:00 pm, Ondrej Certik <ond...@certik.cz> wrote:
> Hi Andrew!
>
>
>
> On Thu, Mar 19, 2009 at 6:20 PM, Andrew <doche...@gmail.com> wrote:
>
> > Hi,
>
> > I have just started using Sympy and find it to be terrific so far, so
> > thanks for all the work you've done in creating it!
>
> > I'm having some problems getting series expansions of some functions,
> > sympy hangs forever (or at least a few hours) for some functions. I've
> > reduced the problem to the simplest case that causes this, and the
> > code appears below. Am I doing something wrong here?
>
> >> from sympy import *
> >> x,a,b = symbols('x,a,b')
> >> f = 1/(1+a*x)
> >> print f.series(x)
>
> > This works fine and prints the series to O(x**6) as expected
>
> >> f = 1/(1+(a+b)*x)
> >> print f.series(x)
>
> > This just hangs and doesn't print anything!
>
> > I am running the latest version of sympy in the git repository.
>
> what an embarrasing bug. I'll try to look at it what went wrong and fix it.
>
> Thanks for discovering it.
>
> Ondrej
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