However when I turn the returned GAP representatives back into elements of
the Sage group (called "weyl_group") sometimes (very rarely) I get
Traceback (most recent call last):
File "/home/vdbergh/TEX/ANYA/anya/scripts/p1xp1/compute_NCCR_orbit.py",
line 353, in <module>
test4("X8")
File "/home/vdbergh/TEX/ANYA/anya/scripts/p1xp1/compute_NCCR_orbit.py",
line 341, in test4
compute_orbit(context, col)
File "/home/vdbergh/TEX/ANYA/anya/scripts/p1xp1/compute_NCCR_orbit.py",
line 41, in compute_orbit
w = weyl_group(w) ** -1 # left coset
^^^^^^^^^^^^^
File "sage/structure/parent.pyx", line 901, in
sage.structure.parent.Parent.__call__
File "sage/structure/coerce_maps.pyx", line 164, in
sage.structure.coerce_maps.DefaultConvertMap_unique._call_
File "sage/structure/coerce_maps.pyx", line 159, in
sage.structure.coerce_maps.DefaultConvertMap_unique._call_
File "/home/vdbergh/sage/src/sage/groups/perm_gps/permgroup.py", line
912, in _element_constructor_
return self.element_class(x, self, check=check)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "sage/groups/perm_gps/permgroup_element.pyx", line 518, in
sage.groups.perm_gps.permgroup_element.PermutationGroupElement.__init__
ValueError: invalid data to initialize a permutation
Anyone knows what could be the cause of this?
Best,
Michel
On Tuesday, February 3, 2026 at 7:22:01 PM UTC+1 Michel VAN DEN BERGH wrote:
> On Tuesday, February 3, 2026 at 7:00:36 PM UTC+1 wrote:
>
> I don't know about efficient, but in the species code I use
> libgap.RightTransveral(group, subgroup):
>
> def structures(self, *labels):
> labels = _label_sets(self.parent()._arity, labels)
> n = tuple([len(U) for U in labels])
> S = _SymmetricGroup(sum(n)).young_subgroup(n)
> l = [e for l in labels for e in l]
> if self._mc == n:
> for rep in libgap.RightTransversal(S, self._dis):
> yield tuple(S(rep)._act_on_list_on_position(l))
>
> Does this help?
>
> Martin
>
>
> Some quick experimenting seems to indicate that this is exactly what I
> need!
>
> Thanks a lot!
>
> Michel
>
>
> On Tuesday, 3 February 2026 at 14:25:12 UTC+1 wrote:
>
> Hi,
>
> I have a permutation group (a Weyl group in fact) and a subgroup given by
> explicit generators. I would like to iterate over representatives for the
> cosets of this group. Is there an efficient way to do this in Sage?
>
> I asked ChatGPT and it gave me all kinds of plausible looking commands,
> none of which actually existed...
>
> Thanks!
>
>
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