The following bug was reported on sage-support, which I was able to reproduce 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 Traceback (most recent call last): ... 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)] I'm confused about why this is happening 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 which I would think should mean that the condition on line 1323 of sage/src/sage/structure/coerce.pyx that the parents are the same should be tripped, but for some reason, it is not. I printed the hash of the parents right before the bug (added it in between lines 1322 and 1323) and they have the same hash (547464660303730434), so I am surprised that they are not considered the same. They are however recognized to be equal, and so the elif statment checking if they are equal (on line 1327) is triggered, but then the coercion of y_elt to parent(x_elt) on line 1329 seems to fail, so that the parent comparison on 1330 still fails, kicking it out to the coercion error. I'm unsure how to fix this but am willing to do the legwork to fix it if anyone can explain the problem. Opening https://trac.sagemath.org/ticket/34292. Full traceback: 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)] -- You received this message because you are subscribed to the Google Groups "sage-devel" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-devel+unsubscr...@googlegroups.com. 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