There is a description/proposed fix of the problem on this trac
ticket: https://trac.sagemath.org/ticket/34292
On Thursday, August 11, 2022 at 12:44:59 PM UTC-7 keirh...@gmail.com wrote:
> This code:
>
>
>
>
> *H = PermutationGroup([ [(1,2), (3,4)], [(5,6,7),(12,14,18)] ])kH =
> H.algebra(GF(2))[a, b] = H.gens()*
>
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> *# 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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>>> .
>>>
>> --
>> Best,
>>
>> Trevor
>>
>
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