This code:
*H = PermutationGroup([ [(1,2), (3,4)], [(5,6,7),(12,14,18)] ])kH =
H.algebra(GF(2))[a, b] = H.gens()# Produces no coercion errorprint((kH(a) +
kH(b) + H.one())^2)# Produces a coercion error in all cases belowtry:
print((kH(a) + kH(b) + kH(kH.one()))^2)except: print("Fail 1")
passtry: print((kH(a) + kH(b) + kH.one())^2)except: print("Fail 2")
passtry: print((kH(a) + kH(b) + kH.group().one())^2)except:
print("Fail 3") passtry: print((kH(a) + kH(b) +
kH(kH.group().one()))^2)except: print("Fail 4") pass*
produces the output:
*(5,7,6)(12,18,14)*
*Fail 1*
*Fail 2*
*Fail 3*
*Fail 4*
The thing that's irritating is that using H.one() in the sum is fine; using
kH.group().one() is not. But I fully admit that I may just not understand
what the right behavior should be.
On Saturday, August 6, 2022 at 11:40:03 PM UTC-4 trevor...@gmail.com wrote:
> Is the x you give in these examples the same x as above? I’m worried
> (maybe needlessly) about if the x you give includes a summand of kH.one().
> If the x you give does not include a summand of one, then the behavior you
> described is consistent with what I think the problem is. If the x in the
> new example doesn’t have a summand of kH.one() then I’m misunderstanding
> something.
>
> On Sat, Aug 6, 2022 at 6:00 PM keirh...@gmail.com <keirh...@gmail.com>
> wrote:
>
>> Thanks for this workaround. I was passing the group algebra to a function
>> and then accessing the base group like so:
>>
>> kH.group()
>>
>> Both of the following cause the coercion error:
>>
>> kH.one() * x
>> kH.group().one() * x
>>
>> But this works fine:
>>
>> H.one()*x
>>
>> I will just have to pass the original group along as well.
>>
>> --Keir
>>
>> On Saturday, August 6, 2022 at 2:06:51 PM UTC-4 trevor...@gmail.com
>> wrote:
>>
>>> I can reproduce this on 9.7.beta7.
>>>
>>> The problem is that the parent is not understood to be the same (even
>>> though it clearly is). A workaround is:
>>>
>>> sage: x = kH(a) + kH(b) + kH(H.one()); x
>>>
>>> () + (5,6,7)(12,14,18) + (1,2)(3,4)
>>>
>>> sage: x*x
>>>
>>> (5,7,6)(12,18,14)
>>>
>>>
>>> Here H.one() puts the one in the right parent for the coercion
>>> framework, but this definitely looks like a bug to me, because
>>>
>>> sage: kH(a).parent()
>>>
>>> Algebra of Permutation Group with generators [(5,6,7)(12,14,18),
>>> (1,2)(3,4)] over Finite Field of size 2
>>>
>>> sage: kH.one().parent()
>>>
>>> Algebra of Permutation Group with generators [(5,6,7)(12,14,18),
>>> (1,2)(3,4)] over Finite Field of size 2
>>>
>>> sage: kH(a).parent() is kH.one().parent()
>>>
>>> True
>>>
>>>
>>> Reproducing the bug with messages on 9.7.beta7:
>>>
>>> sage: H = PermutationGroup([[(*1*,*2*), (*3*,*4*)], [(*5*,*6*,*7*),(*12*
>>> ,*14*,*18*)]])
>>>
>>> sage: kH = H.algebra(GF(*2*))
>>>
>>> sage: H.gens()
>>>
>>> ((5,6,7)(12,14,18), (1,2)(3,4))
>>>
>>> sage: a, b = H.gens()
>>>
>>> sage: x = kH(a) + kH(b) + kH.one(); x
>>>
>>> (5,6,7)(12,14,18) + (1,2)(3,4) + ()
>>>
>>> sage: x*x
>>>
>>>
>>> ---------------------------------------------------------------------------
>>>
>>> RuntimeError Traceback (most recent call
>>> last)
>>>
>>> Input In [7], in <cell line: 1>()
>>>
>>> ----> 1 x*x
>>>
>>>
>>> File ~/Applications/sage/src/sage/structure/element.pyx:1514, in
>>> sage.structure.element.Element.__mul__()
>>>
>>> * 1512* cdef int cl = classify_elements(left, right)
>>>
>>> * 1513* if HAVE_SAME_PARENT(cl):
>>>
>>> -> 1514 return (<Element>left)._mul_(right)
>>>
>>> * 1515* if BOTH_ARE_ELEMENT(cl):
>>>
>>> * 1516* return coercion_model.bin_op(left, right, mul)
>>>
>>>
>>> File ~/Applications/sage/src/sage/structure/element.pyx:1560, in
>>> sage.structure.element.Element._mul_()
>>>
>>> * 1558* raise bin_op_exception('*', self, other)
>>>
>>> * 1559* else:
>>>
>>> -> 1560 return python_op(other)
>>>
>>> * 1561*
>>>
>>> * 1562* cdef _mul_long(self, long n):
>>>
>>>
>>> File ~/Applications/sage/src/sage/categories/coercion_methods.pyx:53, in
>>> sage.categories.coercion_methods._mul_parent()
>>>
>>> * 51* True
>>>
>>> * 52* """
>>>
>>> ---> 53 return (<Element>self)._parent.product(self, other)
>>>
>>>
>>> File ~/Applications/sage/src/sage/categories/magmatic_algebras.py:215,
>>> in
>>> MagmaticAlgebras.WithBasis.ParentMethods._product_from_product_on_basis_multiply(self,
>>>
>>> left, right)
>>>
>>> * 201* *def* _product_from_product_on_basis_multiply( self, left,
>>> right ):
>>>
>>> * 202* r*"""*
>>>
>>> * 203* * Compute the product of two elements by extending*
>>>
>>> * 204* * bilinearly the method :meth:`product_on_basis`.*
>>>
>>> (...)
>>>
>>> * 213*
>>>
>>> * 214* * """*
>>>
>>> --> 215 *return*
>>> self.linear_combination((self.product_on_basis(mon_left, mon_right),
>>> coeff_left * coeff_right )
>>>
>>> * 216* *for* (mon_left,
>>> coeff_left) *in* left.monomial_coefficients().items()
>>>
>>> * 217* *for* (mon_right,
>>> coeff_right) *in* right.monomial_coefficients().items() )
>>>
>>>
>>> File ~/Applications/sage/src/sage/combinat/free_module.py:969, in
>>> CombinatorialFreeModule.linear_combination(self, iter_of_elements_coeff,
>>> factor_on_left)
>>>
>>> * 945* *def* linear_combination(self, iter_of_elements_coeff,
>>> factor_on_left=*True*):
>>>
>>> * 946* r*"""*
>>>
>>> * 947* * Return the linear combination `\lambda_1 v_1 + \cdots +*
>>>
>>> * 948* * \lambda_k v_k` (resp. the linear combination `v_1
>>> \lambda_1 +*
>>>
>>> (...)
>>>
>>> * 967* * 20*B[1] + 20*B[2]*
>>>
>>> * 968* * """*
>>>
>>> --> 969 *return*
>>> self._from_dict(blas.linear_combination(((element._monomial_coefficients,
>>> coeff)
>>>
>>> * 970* *for*
>>> element, coeff *in* iter_of_elements_coeff),
>>>
>>> * 971*
>>> factor_on_left=factor_on_left),
>>>
>>> * 972* remove_zeros=*False*)
>>>
>>>
>>> File ~/Applications/sage/src/sage/data_structures/blas_dict.pyx:313, in
>>> sage.data_structures.blas_dict.linear_combination()
>>>
>>> * 311* return remove_zeros(result)
>>>
>>> * 312*
>>>
>>> --> 313 cpdef dict linear_combination(dict_factor_iter, bint
>>> factor_on_left=True):
>>>
>>> * 314* r"""
>>>
>>> * 315* Return the pointwise addition of dictionaries with
>>> coefficients.
>>>
>>>
>>> File ~/Applications/sage/src/sage/data_structures/blas_dict.pyx:348, in
>>> sage.data_structures.blas_dict.linear_combination()
>>>
>>> * 346* cdef dict D
>>>
>>> * 347*
>>>
>>> --> 348 for D, a in dict_factor_iter:
>>>
>>> * 349* if not a: # We multiply by 0, so nothing to do
>>>
>>> * 350* continue
>>>
>>>
>>> File ~/Applications/sage/src/sage/combinat/free_module.py:969, in
>>> <genexpr>(.0)
>>>
>>> * 945* *def* linear_combination(self, iter_of_elements_coeff,
>>> factor_on_left=*True*):
>>>
>>> * 946* r*"""*
>>>
>>> * 947* * Return the linear combination `\lambda_1 v_1 + \cdots +*
>>>
>>> * 948* * \lambda_k v_k` (resp. the linear combination `v_1
>>> \lambda_1 +*
>>>
>>> (...)
>>>
>>> * 967* * 20*B[1] + 20*B[2]*
>>>
>>> * 968* * """*
>>>
>>> --> 969 *return*
>>> self._from_dict(blas.linear_combination(((element._monomial_coefficients,
>>> coeff)
>>>
>>> * 970* *for*
>>> element, coeff *in* iter_of_elements_coeff),
>>>
>>> * 971*
>>> factor_on_left=factor_on_left),
>>>
>>> * 972* remove_zeros=*False*)
>>>
>>>
>>> File ~/Applications/sage/src/sage/categories/magmatic_algebras.py:215,
>>> in <genexpr>(.0)
>>>
>>> * 201* *def* _product_from_product_on_basis_multiply( self, left,
>>> right ):
>>>
>>> * 202* r*"""*
>>>
>>> * 203* * Compute the product of two elements by extending*
>>>
>>> * 204* * bilinearly the method :meth:`product_on_basis`.*
>>>
>>> (...)
>>>
>>> * 213*
>>>
>>> * 214* * """*
>>>
>>> --> 215 *return*
>>> self.linear_combination((self.product_on_basis(mon_left, mon_right),
>>> coeff_left * coeff_right )
>>>
>>> * 216* *for* (mon_left,
>>> coeff_left) *in* left.monomial_coefficients().items()
>>>
>>> * 217* *for* (mon_right,
>>> coeff_right) *in* right.monomial_coefficients().items() )
>>>
>>>
>>> File ~/Applications/sage/src/sage/categories/semigroups.py:957, in
>>> Semigroups.Algebras.ParentMethods.product_on_basis(self, g1, g2)
>>>
>>> * 939* *def* product_on_basis(self, g1, g2):
>>>
>>> * 940* r*"""*
>>>
>>> * 941* * Product, on basis elements, as per*
>>>
>>> * 942* *
>>> :meth:`MagmaticAlgebras.WithBasis.ParentMethods.product_on_basis()*
>>>
>>> (...)
>>>
>>> * 955* * B['ab'] + B['bdc']*
>>>
>>> * 956* * """*
>>>
>>> --> 957 *return* self.monomial(g1 * g2)
>>>
>>>
>>> File
>>> ~/Applications/sage/src/sage/groups/perm_gps/permgroup_element.pyx:1295, in
>>> sage.groups.perm_gps.permgroup_element.PermutationGroupElement.__mul__()
>>>
>>> * 1293* return prod
>>>
>>> * 1294*
>>>
>>> -> 1295 return coercion_model.bin_op(left, right, operator.mul)
>>>
>>> * 1296*
>>>
>>> * 1297* cpdef _mul_(left, _right):
>>>
>>>
>>> File ~/Applications/sage/src/sage/structure/coerce.pyx:1200, in
>>> sage.structure.coerce.CoercionModel.bin_op()
>>>
>>> * 1198* # Now coerce to a common parent and do the operation there
>>>
>>> * 1199* try:
>>>
>>> -> 1200 xy = self.canonical_coercion(x, y)
>>>
>>> * 1201* except TypeError:
>>>
>>> * 1202* self._record_exception()
>>>
>>>
>>> File ~/Applications/sage/src/sage/structure/coerce.pyx:1332, in
>>> sage.structure.coerce.CoercionModel.canonical_coercion()
>>>
>>> * 1330* if x_elt._parent is y_elt._parent:
>>>
>>> * 1331* return x_elt,y_elt
>>>
>>> -> 1332 self._coercion_error(x, x_map, x_elt, y, y_map, y_elt)
>>>
>>> * 1333*
>>>
>>> * 1334* cdef bint x_numeric = isinstance(x, (int, long, float,
>>> complex))
>>>
>>>
>>> File ~/Applications/sage/src/sage/structure/coerce.pyx:2031, in
>>> sage.structure.coerce.CoercionModel._coercion_error()
>>>
>>> * 2029* <class 'str'> 'g'
>>>
>>> * 2030* """
>>>
>>> -> 2031 raise RuntimeError("""There is a bug in the coercion
>>> code in Sage.
>>>
>>> * 2032* Both x (=%r) and y (=%r) are supposed to have identical
>>> parents but they don't.
>>>
>>> * 2033* In fact, x has parent '%s'
>>>
>>>
>>> RuntimeError: There is a bug in the coercion code in Sage.
>>>
>>> Both x (=()) and y (=(5,6,7)(12,14,18)) are supposed to have identical
>>> parents but they don't.
>>>
>>> In fact, x has parent 'Permutation Group with generators
>>> [(5,6,7)(12,14,18), (1,2)(3,4)]'
>>>
>>> whereas y has parent 'Permutation Group with generators
>>> [(5,6,7)(12,14,18), (1,2)(3,4)]'
>>>
>>> Original elements () (parent Permutation Group with generators
>>> [(5,6,7)(12,14,18), (1,2)(3,4)]) and (5,6,7)(12,14,18) (parent Permutation
>>> Group with generators [(5,6,7)(12,14,18), (1,2)(3,4)]) and maps
>>>
>>> <class 'NoneType'> None
>>>
>>> <class 'sage.structure.coerce_maps.DefaultConvertMap_unique'> (map
>>> internal to coercion system -- copy before use)
>>>
>>> Coercion map:
>>>
>>> From: Permutation Group with generators [(5,6,7)(12,14,18), (1,2)(3,4)]
>>>
>>> To: Permutation Group with generators [(5,6,7)(12,14,18), (1,2)(3,4)]
>>> On Friday, August 5, 2022 at 4:21:09 PM UTC-7 keirh...@gmail.com wrote:
>>>
>>>> The Sage version I was using is 9.6.
>>>>
>>>> On Friday, August 5, 2022 at 7:19:48 PM UTC-4 keirh...@gmail.com wrote:
>>>>
>>>>> When I do this:
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> *H = PermutationGroup([ [(1,2), (3,4)], [(5,6,7),(12,14,18)] ])kH =
>>>>> H.algebra(GF(2))[a, b] = H.gens()x = kH(a) + kH(b) + kH.one();
>>>>> print(x)x*x*
>>>>>
>>>>> I get an error caused by the last computation: "RuntimeError: There is
>>>>> a bug in the coercion code in Sage." (I was working in Cocalc, but you
>>>>> can
>>>>> cut and paste the code above into a SageMathCell and reproduce the error.)
>>>>>
>>>>> Is this really a bug, or should I be doing this differently? (I found
>>>>> the problem working with a larger group, but this simpler example above
>>>>> has
>>>>> the same issue.)
>>>>>
>>>>> Thanks --
>>>>>
>>>>> Keir
>>>>>
>>>> --
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>>
>> <https://groups.google.com/d/msgid/sage-support/d7fbbb32-5ea3-45d8-8ca6-6c5da0088bban%40googlegroups.com?utm_medium=email&utm_source=footer>
>> .
>>
> --
> Best,
>
> Trevor
>
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