#9831: Permutation(list) should check its input (?)
-----------------------------+----------------------------------------------
Reporter: mmezzarobba | Owner: sage-combinat
Type: defect | Status: new
Priority: major | Milestone: sage-4.5.3
Component: combinatorics | Keywords:
Author: | Upstream: N/A
Reviewer: | Merged:
Work_issues: |
-----------------------------+----------------------------------------------
Description changed by mmezzarobba:
Old description:
> {{{
> ~$ ulimit -v 1048576
> ~$ sage
> ----------------------------------------------------------------------
> | Sage Version 4.5.1, Release Date: 2010-07-19 |
> | Type notebook() for the GUI, and license() for information. |
> ----------------------------------------------------------------------
> sage: Permutation([1]).signature()
> 1
> sage: Permutation([0]).signature()
> -1
> sage: Permutation([1,0]).signature()
> -1
> sage: Permutation([0,1]).signature()
> ---------------------------------------------------------------------------
> MemoryError Traceback (most recent call
> last)
>
> /home/marc/<ipython console> in <module>()
>
> /data/sage-4.5.1/local/lib/python2.6/site-
> packages/sage/combinat/permutation.pyc in signature(p)
> 739 -1
> 740 """
> --> 741 return (-1)**(len(p)-len(p.to_cycles()))
> 742
> 743
>
> /data/sage-4.5.1/local/lib/python2.6/site-
> packages/sage/combinat/permutation.pyc in to_cycles(self, singletons)
> 556 l[i], next = False, l[i]
> 557 while next != cycleFirst:
> --> 558 cycle.append( next )
> 559 l[next - 1], next = False, l[next - 1]
> 560 #Add the cycle to the list of cycles
>
> MemoryError:
> }}}
New description:
It seems that ``Permutation(list)`` requires that the elements of list are
exactly 1, 2, ..., n, but this is not clearly documented. Other values of
``list`` are accepted without error and lead to strange behaviours later.
When ``list`` contains 0:
{{{
~$ ulimit -v 1048576
~$ sage
----------------------------------------------------------------------
| Sage Version 4.5.1, Release Date: 2010-07-19 |
| Type notebook() for the GUI, and license() for information. |
----------------------------------------------------------------------
sage: Permutation([1]).signature()
1
sage: Permutation([0]).signature()
-1
sage: Permutation([1,0]).signature()
-1
sage: Permutation([0,1]).signature()
---------------------------------------------------------------------------
MemoryError Traceback (most recent call
last)
/home/marc/<ipython console> in <module>()
/data/sage-4.5.1/local/lib/python2.6/site-
packages/sage/combinat/permutation.pyc in signature(p)
739 -1
740 """
--> 741 return (-1)**(len(p)-len(p.to_cycles()))
742
743
/data/sage-4.5.1/local/lib/python2.6/site-
packages/sage/combinat/permutation.pyc in to_cycles(self, singletons)
556 l[i], next = False, l[i]
557 while next != cycleFirst:
--> 558 cycle.append( next )
559 l[next - 1], next = False, l[next - 1]
560 #Add the cycle to the list of cycles
MemoryError:
}}}
With repeated elements:
{{{
sage: Permutation([1,1]).signature()
---------------------------------------------------------------------------
MemoryError Traceback (most recent call
last)
/home/marc/<ipython console> in <module>()
/data/sage-4.5.1/local/lib/python2.6/site-
packages/sage/combinat/permutation.pyc in signature(p)
739 -1
740 """
--> 741 return (-1)**(len(p)-len(p.to_cycles()))
742
743
/data/sage-4.5.1/local/lib/python2.6/site-
packages/sage/combinat/permutation.pyc in to_cycles(self, singletons)
556 l[i], next = False, l[i]
557 while next != cycleFirst:
--> 558 cycle.append( next )
559 l[next - 1], next = False, l[next - 1]
560 #Add the cycle to the list of cycles
MemoryError:
}}}
--
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/9831#comment:1>
Sage <http://www.sagemath.org>
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