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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