#14685: error in the computing of the approximate order in LazyPowerSeries
------------------------------------------------------------+---------------
Reporter: MatthieuDien | Owner:
sage-combinat
Type: defect | Status:
new
Priority: major | Milestone:
sage-5.10
Component: combinatorics | Resolution:
Keywords: LazyPowerSeries aorder approximate order | Work issues:
Report Upstream: N/A | Reviewers:
Authors: | Merged in:
Dependencies: | Stopgaps:
------------------------------------------------------------+---------------
Description changed by MatthieuDien:
Old description:
> Hi,
>
> I found a bug in the LazyPowerSeries class of package combinat.
> There is mistake in the computing of the approximate order of a serie.
> A demonstration of the bug :
> {{{
> sage: R = LazyPowerSeriesRing(QQ)
> sage: B = R([0,0,0,1,0])
> sage: B.aorder
> 0
> sage: B.coefficients(10)
> [0, 0, 0, 1, 0, 0, 0, 0, 0, 0]
> sage: B.aorder
> 1
> }}}
>
> Here, a patch :
> {{{
> diff --git a/sage/combinat/species/series.py
> b/sage/combinat/species/series.py
> --- a/sage/combinat/species/series.py
> +++ b/sage/combinat/species/series.py
> @@ -631,6 +631,7 @@
> self.aorder += 1
> ao += 1
> else:
> + self.order = ao
> break
>
> #Try to recognize the zero series
> @@ -643,8 +644,17 @@
> self.order = inf
> return
>
> - if ao < n:
> - self.order = ao
> + if self.order == unk:
> + while ao < n:
> + if self._stream[ao] == 0:
> + self.aorder += 1
> + ao += 1
> + else:
> + self.order = ao
> + break
> +
> + # if ao < n:
> + # self.order = ao
>
> if hasattr(self, '_reference') and self._reference is not None:
> }}}
>
> I commited it with the number 18037 on the mercurial server
>
> It's my first patch, sorry if i did a mistake.
New description:
Hi,
I found a bug in the LazyPowerSeries class of package combinat.
There is mistake in the computing of the approximate order of a serie.
A demonstration of the bug :
{{{
sage: R = LazyPowerSeriesRing(QQ)
sage: B = R([0,0,0,1,0])
sage: B.aorder
0
sage: B.coefficients(10)
[0, 0, 0, 1, 0, 0, 0, 0, 0, 0]
sage: B.aorder
1
}}}
The good result should be 3 and not 1 (the order of the series B = x^3 is
3 not 1 )
Here, a patch which fix that:
{{{
--- series_old.py 2013-06-08 13:48:40.490566975 +0200
+++ series.py 2013-06-08 14:00:41.903399503 +0200
@@ -624,17 +624,17 @@
c = self._stream
n = c.number_computed()
+ while ao < n:
+ if self._stream[ao] == 0:
+ self.aorder += 1
+ ao += 1
+ else:
+ self.order = ao
+ break
- if ao == 0 and n > 0:
- while ao < n:
- if self._stream[ao] == 0:
- self.aorder += 1
- ao += 1
- else:
- break
#Try to recognize the zero series
- if ao == n:
+ if ao == n and n > 0:
#For non-constant series, we cannot do anything
if not c.is_constant():
return
@@ -642,11 +642,7 @@
self.aorder = inf
self.order = inf
return
-
- if ao < n:
- self.order = ao
-
-
+
if hasattr(self, '_reference') and self._reference is not None:
self._reference._copy(self)
}}}
The bug is that the aorder is computed one time and never updated. This is
because the order was assigned the first time then the condition
self.order != unk becomes false and the update never comes.
After the patch, we obtain :
{{{
sage: R = LazyPowerSeriesRing(QQ)
sage: B = R([0,0,0,1,0])
sage: B.aorder
0
sage: B.coefficients(10)
[0, 0, 0, 1, 0, 0, 0, 0, 0, 0]
sage: B.aorder
3
}}}
What we expected.
PS : Thanks you for the commment, I tried to answer.
--
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/14685#comment:3>
Sage <http://www.sagemath.org>
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