Thanks for the other command. I am writing a tutorial for my university and
am running into quite a few of these little gotcha's with these sort of
things.
--
D. M. Monarres
<dmmonar...@gmail.com>
On Tue, Jan 18, 2011 at 8:28 PM, John H Palmieri <jhpalmier...@gmail.com>wrote:
> On Jan 18, 7:30 pm, "D. M. Monarres" <dmmonar...@gmail.com> wrote:
> > Hello all,
> >
> > Running into an issue with something. I must be missing something. Say I
> > construct two groups that I know are isomorphic.
> >
> > sage: G = SymmetricGroup(5)
> > sage: r = G('(1,2,5,4,3)')
> > sage: s = G('(1,5),(3,4)')
> > sage: H = G.subgroup([r,s])
> > sage: H
> > Subgroup of SymmetricGroup(5) generated by [(1,2,5,4,3), (1,5)(3,4)]
> > sage: D = DihedralGroup(5)
> > sage: D
> > Dihedral group of order 10 as a permutation group
> >
> > I get an TypeError when I try and construct a homomorphism between these
> two
> > groups.
> > sage: phi = D.hom( ['(1,2,5,4,3)', '(1,5)(3,4)'] , H)
> >
> ---------------------------------------------------------------------------
> > TypeError Traceback (most recent call
> last)
> >
> > /Users/ayeq/Dropbox/src/sdsu-sage-tutorial/<ipython console> in
> <module>()
> >
> >
> /Users/ayeq/sage/local/lib/python2.6/site-packages/sage/structure/parent_ge
> ns.so
> > in sage.structure.parent_gens.ParentWithGens.hom
> > (sage/structure/parent_gens.c:3858)()
> >
> >
> /Users/ayeq/sage/local/lib/python2.6/site-packages/sage/categories/homset.p
> yc
> > in __call__(self, x, y, check, on_basis)
> > 432 return self.element_class_set_morphism(self, x)
> > 433
> > --> 434 raise TypeError, "Unable to coerce x (=%s) to a morphism
> in
> > %s"%(x,self)
> > 435
> > 436 @lazy_attribute
> >
> > TypeError: Unable to coerce x (=['(1,2,5,4,3)', '(1,5)(3,4)']) to a
> morphism
> > in Set of Morphisms from Dihedral group of order 10 as a permutation
> group
> > to Subgroup of SymmetricGroup(5) generated by [(1,2,5,4,3), (1,5)(3,4)]
> in
> > Category of finite permutation groups
> >
> > I have tried to do this in a few different ways. (by coercing the
> elements
> > first, etc...) Can somebody see what I am missing? Thank you in advance.
>
> This looks like a bug to me, but I'm not sure. Anyway, you can do
> this:
>
> sage: PermutationGroupMorphism(D, H, D.gens(), H.gens())
> Homomorphism : Dihedral group of order 10 as a permutation group -->
> Subgroup of SymmetricGroup(5) generated by [(1,2,5,4,3), (1,5)(3,4)]
>
> (I don't know why "D.hom(H.gens(), H)" doesn't do the same thing...)
>
> --
> John
>
> --
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