Opened 5 months ago

Last modified 4 months ago

#27881 new defect

allow creation of PermutationGroupElement with 0 in domain

Reported by: dimpase Owned by:
Priority: major Milestone:
Component: group theory Keywords:
Cc: dcoudert, stumpc5 Merged in:
Authors: Reviewers:
Report Upstream: N/A Work issues:
Branch: Commit:
Dependencies: Stopgaps:

Description

one can create PermutationGroup_generic_with_category acting on a domain with 0, but creating its individual elements (moving 0) is broken.

sage: p=graphs.PetersenGraph()
sage: a=p.automorphism_group(); a
Permutation Group with generators [(3,7)(4,5)(8,9), (2,6)(3,8)(4,5)(7,9), (1,4,5)(2,3,8,6,9,7), (0,1)(2,4,6,5)(3,9,8,7)]
sage: a.domain()
{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
sage: map(type, a.gens())
[<type 'sage.groups.perm_gps.permgroup_element.PermutationGroupElement'>,
 <type 'sage.groups.perm_gps.permgroup_element.PermutationGroupElement'>,
 <type 'sage.groups.perm_gps.permgroup_element.PermutationGroupElement'>,
 <type 'sage.groups.perm_gps.permgroup_element.PermutationGroupElement'>]
sage: PermutationGroupElement("(0,2)")
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-15-fa3d3058e13a> in <module>()
----> 1 PermutationGroupElement("(0,2)")

/home/dimpase/Sage/sagetrac-mirror/local/lib/python2.7/site-packages/sage/groups/perm_gps/permgroup_element.pyx in sage.groups.perm_gps.permgroup_element.PermutationGroupElement.__init__ (build/cythonized/sage/groups/perm_gps/permgroup_element.c:5852)()
    502 
    503         degree = max([1] + [max(cycle+(1,)) for cycle in v])
--> 504         v = from_cycles(degree, v)
    505 
    506         self.__gap = 'PermList({})'.format(list(v)) # Make sure it is a list

/home/dimpase/Sage/sagetrac-mirror/local/lib/python2.7/site-packages/sage/combinat/permutation.pyc in from_cycles(n, cycles, parent)
   7041     # Only positive elements
   7042     if int(flattened_and_sorted[0]) < 1:
-> 7043         raise ValueError("All elements should be strictly positive "
   7044                          "integers, and I just found a non-positive one.")
   7045 

ValueError: All elements should be strictly positive integers, and I just found a non-positive one.

Change History (1)

comment:1 Changed 4 months ago by embray

  • Milestone sage-8.8 deleted

As the Sage-8.8 release milestone is pending, we should delete the sage-8.8 milestone for tickets that are not actively being worked on or that still require significant work to move forward. If you feel that this ticket should be included in the next Sage release at the soonest please set its milestone to the next release milestone (sage-8.9).

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