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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