X-Git-Url: http://gitweb.michael.orlitzky.com/?a=blobdiff_plain;f=mjo%2Feja%2Feja_algebra.py;h=ca3df5fea55949225a51f8255a2c13a33c37d9f2;hb=7f55521ab4652d3ca10cd085f8e9d41bf149e8e5;hp=ee34e532fa7f4efb3d5aa7d89001f0430f2df52d;hpb=da5bbdc1e0e0a2e020a15b48a3e90d8cee0dfb10;p=sage.d.git diff --git a/mjo/eja/eja_algebra.py b/mjo/eja/eja_algebra.py index ee34e53..ca3df5f 100644 --- a/mjo/eja/eja_algebra.py +++ b/mjo/eja/eja_algebra.py @@ -32,22 +32,25 @@ for these simple algebras: * :class:`RealSymmetricEJA` * :class:`ComplexHermitianEJA` * :class:`QuaternionHermitianEJA` + * :class:`OctonionHermitianEJA` -Missing from this list is the algebra of three-by-three octononion -Hermitian matrices, as there is (as of yet) no implementation of the -octonions in SageMath. In addition to these, we provide two other -example constructions, +In addition to these, we provide two other example constructions, + * :class:`JordanSpinEJA` * :class:`HadamardEJA` + * :class:`AlbertEJA` * :class:`TrivialEJA` The Jordan spin algebra is a bilinear form algebra where the bilinear form is the identity. The Hadamard EJA is simply a Cartesian product -of one-dimensional spin algebras. And last but not least, the trivial -EJA is exactly what you think. Cartesian products of these are also -supported using the usual ``cartesian_product()`` function; as a -result, we support (up to isomorphism) all Euclidean Jordan algebras -that don't involve octonions. +of one-dimensional spin algebras. The Albert EJA is simply a special +case of the :class:`OctonionHermitianEJA` where the matrices are +three-by-three and the resulting space has dimension 27. And +last/least, the trivial EJA is exactly what you think it is; it could +also be obtained by constructing a dimension-zero instance of any of +the other algebras. Cartesian products of these are also supported +using the usual ``cartesian_product()`` function; as a result, we +support (up to isomorphism) all Euclidean Jordan algebras. SETUP:: @@ -59,13 +62,10 @@ EXAMPLES:: Euclidean Jordan algebra of dimension... """ -from itertools import repeat - from sage.algebras.quatalg.quaternion_algebra import QuaternionAlgebra from sage.categories.magmatic_algebras import MagmaticAlgebras from sage.categories.sets_cat import cartesian_product -from sage.combinat.free_module import (CombinatorialFreeModule, - CombinatorialFreeModule_CartesianProduct) +from sage.combinat.free_module import CombinatorialFreeModule from sage.matrix.constructor import matrix from sage.matrix.matrix_space import MatrixSpace from sage.misc.cachefunc import cached_method @@ -112,6 +112,23 @@ class FiniteDimensionalEJA(CombinatorialFreeModule): generally rules out using the rationals as your ``field``, but is required for spectral decompositions. + SETUP:: + + sage: from mjo.eja.eja_algebra import random_eja + + TESTS: + + We should compute that an element subalgebra is associative even + if we circumvent the element method:: + + sage: set_random_seed() + sage: J = random_eja(field=QQ,orthonormalize=False) + sage: x = J.random_element() + sage: A = x.subalgebra_generated_by(orthonormalize=False) + sage: basis = tuple(b.superalgebra_element() for b in A.basis()) + sage: J.subalgebra(basis, orthonormalize=False).is_associative() + True + """ Element = FiniteDimensionalEJAElement @@ -121,23 +138,13 @@ class FiniteDimensionalEJA(CombinatorialFreeModule): inner_product, field=AA, orthonormalize=True, - associative=False, + associative=None, cartesian_product=False, check_field=True, check_axioms=True, - prefix='e'): - - # Keep track of whether or not the matrix basis consists of - # tuples, since we need special cases for them damned near - # everywhere. This is INDEPENDENT of whether or not the - # algebra is a cartesian product, since a subalgebra of a - # cartesian product will have a basis of tuples, but will not - # in general itself be a cartesian product algebra. - self._matrix_basis_is_cartesian = False + prefix="b"): + n = len(basis) - if n > 0: - if hasattr(basis[0], 'cartesian_factors'): - self._matrix_basis_is_cartesian = True if check_field: if not field.is_subring(RR): @@ -146,21 +153,6 @@ class FiniteDimensionalEJA(CombinatorialFreeModule): # we've specified a real embedding. raise ValueError("scalar field is not real") - # If the basis given to us wasn't over the field that it's - # supposed to be over, fix that. Or, you know, crash. - if not cartesian_product: - # The field for a cartesian product algebra comes from one - # of its factors and is the same for all factors, so - # there's no need to "reapply" it on product algebras. - if self._matrix_basis_is_cartesian: - # OK since if n == 0, the basis does not consist of tuples. - P = basis[0].parent() - basis = tuple( P(tuple(b_i.change_ring(field) for b_i in b)) - for b in basis ) - else: - basis = tuple( b.change_ring(field) for b in basis ) - - if check_axioms: # Check commutativity of the Jordan and inner-products. # This has to be done before we build the multiplication @@ -180,11 +172,26 @@ class FiniteDimensionalEJA(CombinatorialFreeModule): category = MagmaticAlgebras(field).FiniteDimensional() category = category.WithBasis().Unital().Commutative() + if associative is None: + # We should figure it out. As with check_axioms, we have to do + # this without the help of the _jordan_product_is_associative() + # method because we need to know the category before we + # initialize the algebra. + associative = all( jordan_product(jordan_product(bi,bj),bk) + == + jordan_product(bi,jordan_product(bj,bk)) + for bi in basis + for bj in basis + for bk in basis) + if associative: # Element subalgebras can take advantage of this. category = category.Associative() if cartesian_product: - category = category.CartesianProducts() + # Use join() here because otherwise we only get the + # "Cartesian product of..." and not the things themselves. + category = category.join([category, + category.CartesianProducts()]) # Call the superclass constructor so that we can use its from_vector() # method to build our multiplication table. @@ -199,7 +206,7 @@ class FiniteDimensionalEJA(CombinatorialFreeModule): # ambient vector space V that our (vectorized) basis lives in, # as well as a subspace W of V spanned by those (vectorized) # basis elements. The W-coordinates are the coefficients that - # we see in things like x = 1*e1 + 2*e2. + # we see in things like x = 1*b1 + 2*b2. vector_basis = basis degree = 0 @@ -326,16 +333,16 @@ class FiniteDimensionalEJA(CombinatorialFreeModule): sage: set_random_seed() sage: J = random_eja() sage: n = J.dimension() - sage: ei = J.zero() - sage: ej = J.zero() - sage: ei_ej = J.zero()*J.zero() + sage: bi = J.zero() + sage: bj = J.zero() + sage: bi_bj = J.zero()*J.zero() sage: if n > 0: ....: i = ZZ.random_element(n) ....: j = ZZ.random_element(n) - ....: ei = J.gens()[i] - ....: ej = J.gens()[j] - ....: ei_ej = J.product_on_basis(i,j) - sage: ei*ej == ei_ej + ....: bi = J.monomial(i) + ....: bj = J.monomial(j) + ....: bi_bj = J.product_on_basis(i,j) + sage: bi*bj == bi_bj True """ @@ -431,9 +438,7 @@ class FiniteDimensionalEJA(CombinatorialFreeModule): this algebra was constructed with ``check_axioms=False`` and passed an invalid multiplication table. """ - return all( self.product_on_basis(i,j) == self.product_on_basis(i,j) - for i in range(self.dimension()) - for j in range(self.dimension()) ) + return all( x*y == y*x for x in self.gens() for y in self.gens() ) def _is_jordanian(self): r""" @@ -446,9 +451,9 @@ class FiniteDimensionalEJA(CombinatorialFreeModule): return ``True``, unless this algebra was constructed with ``check_axioms=False`` and passed an invalid multiplication table. """ - return all( (self.gens()[i]**2)*(self.gens()[i]*self.gens()[j]) + return all( (self.monomial(i)**2)*(self.monomial(i)*self.monomial(j)) == - (self.gens()[i])*((self.gens()[i]**2)*self.gens()[j]) + (self.monomial(i))*((self.monomial(i)**2)*self.monomial(j)) for i in range(self.dimension()) for j in range(self.dimension()) ) @@ -464,7 +469,8 @@ class FiniteDimensionalEJA(CombinatorialFreeModule): SETUP:: - sage: from mjo.eja.eja_algebra import (RealSymmetricEJA, + sage: from mjo.eja.eja_algebra import (random_eja, + ....: RealSymmetricEJA, ....: ComplexHermitianEJA, ....: QuaternionHermitianEJA) @@ -498,6 +504,16 @@ class FiniteDimensionalEJA(CombinatorialFreeModule): sage: A._jordan_product_is_associative() True + TESTS: + + The values we've presupplied to the constructors agree with + the computation:: + + sage: set_random_seed() + sage: J = random_eja() + sage: J.is_associative() == J._jordan_product_is_associative() + True + """ R = self.base_ring() @@ -517,9 +533,9 @@ class FiniteDimensionalEJA(CombinatorialFreeModule): for i in range(self.dimension()): for j in range(self.dimension()): for k in range(self.dimension()): - x = self.gens()[i] - y = self.gens()[j] - z = self.gens()[k] + x = self.monomial(i) + y = self.monomial(j) + z = self.monomial(k) diff = (x*y)*z - x*(y*z) if diff.norm() > epsilon: @@ -548,9 +564,9 @@ class FiniteDimensionalEJA(CombinatorialFreeModule): for i in range(self.dimension()): for j in range(self.dimension()): for k in range(self.dimension()): - x = self.gens()[i] - y = self.gens()[j] - z = self.gens()[k] + x = self.monomial(i) + y = self.monomial(j) + z = self.monomial(k) diff = (x*y).inner_product(z) - x.inner_product(y*z) if diff.abs() > epsilon: @@ -598,7 +614,7 @@ class FiniteDimensionalEJA(CombinatorialFreeModule): sage: J2 = RealSymmetricEJA(2) sage: J = cartesian_product([J1,J2]) sage: J( (J1.matrix_basis()[1], J2.matrix_basis()[2]) ) - e(0, 1) + e(1, 2) + b1 + b5 TESTS: @@ -873,15 +889,15 @@ class FiniteDimensionalEJA(CombinatorialFreeModule): sage: J = JordanSpinEJA(4) sage: J.multiplication_table() +----++----+----+----+----+ - | * || e0 | e1 | e2 | e3 | + | * || b0 | b1 | b2 | b3 | +====++====+====+====+====+ - | e0 || e0 | e1 | e2 | e3 | + | b0 || b0 | b1 | b2 | b3 | +----++----+----+----+----+ - | e1 || e1 | e0 | 0 | 0 | + | b1 || b1 | b0 | 0 | 0 | +----++----+----+----+----+ - | e2 || e2 | 0 | e0 | 0 | + | b2 || b2 | 0 | b0 | 0 | +----++----+----+----+----+ - | e3 || e3 | 0 | 0 | e0 | + | b3 || b3 | 0 | 0 | b0 | +----++----+----+----+----+ """ @@ -891,7 +907,7 @@ class FiniteDimensionalEJA(CombinatorialFreeModule): # And to each subsequent row, prepend an entry that belongs to # the left-side "header column." - M += [ [self.gens()[i]] + [ self.product_on_basis(i,j) + M += [ [self.monomial(i)] + [ self.monomial(i)*self.monomial(j) for j in range(n) ] for i in range(n) ] @@ -935,7 +951,7 @@ class FiniteDimensionalEJA(CombinatorialFreeModule): sage: J = RealSymmetricEJA(2) sage: J.basis() - Finite family {0: e0, 1: e1, 2: e2} + Finite family {0: b0, 1: b1, 2: b2} sage: J.matrix_basis() ( [1 0] [ 0 0.7071067811865475?] [0 0] @@ -946,7 +962,7 @@ class FiniteDimensionalEJA(CombinatorialFreeModule): sage: J = JordanSpinEJA(2) sage: J.basis() - Finite family {0: e0, 1: e1} + Finite family {0: b0, 1: b1} sage: J.matrix_basis() ( [1] [0] @@ -1028,20 +1044,20 @@ class FiniteDimensionalEJA(CombinatorialFreeModule): sage: J = HadamardEJA(5) sage: J.one() - e0 + e1 + e2 + e3 + e4 + b0 + b1 + b2 + b3 + b4 The unit element in the Hadamard EJA is inherited in the subalgebras generated by its elements:: sage: J = HadamardEJA(5) sage: J.one() - e0 + e1 + e2 + e3 + e4 + b0 + b1 + b2 + b3 + b4 sage: x = sum(J.gens()) sage: A = x.subalgebra_generated_by(orthonormalize=False) sage: A.one() - f0 + c0 sage: A.one().superalgebra_element() - e0 + e1 + e2 + e3 + e4 + b0 + b1 + b2 + b3 + b4 TESTS: @@ -1393,7 +1409,7 @@ class FiniteDimensionalEJA(CombinatorialFreeModule): def L_x_i_j(i,j): # From a result in my book, these are the entries of the # basis representation of L_x. - return sum( vars[k]*self.gens()[k].operator().matrix()[i,j] + return sum( vars[k]*self.monomial(k).operator().matrix()[i,j] for k in range(n) ) L_x = matrix(F, n, n, L_x_i_j) @@ -1528,7 +1544,7 @@ class FiniteDimensionalEJA(CombinatorialFreeModule): class RationalBasisEJA(FiniteDimensionalEJA): r""" - New class for algebras whose supplied basis elements have all rational entries. + Algebras whose supplied basis elements have all rational entries. SETUP:: @@ -1562,6 +1578,13 @@ class RationalBasisEJA(FiniteDimensionalEJA): if not all( all(b_i in QQ for b_i in b.list()) for b in basis ): raise TypeError("basis not rational") + super().__init__(basis, + jordan_product, + inner_product, + field=field, + check_field=check_field, + **kwargs) + self._rational_algebra = None if field is not QQ: # There's no point in constructing the extra algebra if this @@ -1575,17 +1598,11 @@ class RationalBasisEJA(FiniteDimensionalEJA): jordan_product, inner_product, field=QQ, + associative=self.is_associative(), orthonormalize=False, check_field=False, check_axioms=False) - super().__init__(basis, - jordan_product, - inner_product, - field=field, - check_field=check_field, - **kwargs) - @cached_method def _charpoly_coefficients(self): r""" @@ -1640,7 +1657,7 @@ class RationalBasisEJA(FiniteDimensionalEJA): subs_dict = { X[i]: BX[i] for i in range(len(X)) } return tuple( a_i.subs(subs_dict) for a_i in a ) -class ConcreteEJA(RationalBasisEJA): +class ConcreteEJA(FiniteDimensionalEJA): r""" A class for the Euclidean Jordan algebras that we know by name. @@ -1709,6 +1726,19 @@ class ConcreteEJA(RationalBasisEJA): class MatrixEJA: + @staticmethod + def jordan_product(X,Y): + return (X*Y + Y*X)/2 + + @staticmethod + def trace_inner_product(X,Y): + r""" + A trace inner-product for matrices that aren't embedded in the + reals. It takes MATRICES as arguments, not EJA elements. + """ + return (X*Y).trace().real() + +class RealEmbeddedMatrixEJA(MatrixEJA): @staticmethod def dimension_over_reals(): r""" @@ -1754,9 +1784,6 @@ class MatrixEJA: raise ValueError("the matrix 'M' must be a real embedding") return M - @staticmethod - def jordan_product(X,Y): - return (X*Y + Y*X)/2 @classmethod def trace_inner_product(cls,X,Y): @@ -1765,29 +1792,11 @@ class MatrixEJA: SETUP:: - sage: from mjo.eja.eja_algebra import (RealSymmetricEJA, - ....: ComplexHermitianEJA, + sage: from mjo.eja.eja_algebra import (ComplexHermitianEJA, ....: QuaternionHermitianEJA) EXAMPLES:: - This gives the same answer as it would if we computed the trace - from the unembedded (original) matrices:: - - sage: set_random_seed() - sage: J = RealSymmetricEJA.random_instance() - sage: x,y = J.random_elements(2) - sage: Xe = x.to_matrix() - sage: Ye = y.to_matrix() - sage: X = J.real_unembed(Xe) - sage: Y = J.real_unembed(Ye) - sage: expected = (X*Y).trace() - sage: actual = J.trace_inner_product(Xe,Ye) - sage: actual == expected - True - - :: - sage: set_random_seed() sage: J = ComplexHermitianEJA.random_instance() sage: x,y = J.random_elements(2) @@ -1815,27 +1824,15 @@ class MatrixEJA: True """ - Xu = cls.real_unembed(X) - Yu = cls.real_unembed(Y) - tr = (Xu*Yu).trace() + # This does in fact compute the real part of the trace. + # If we compute the trace of e.g. a complex matrix M, + # then we do so by adding up its diagonal entries -- + # call them z_1 through z_n. The real embedding of z_1 + # will be a 2-by-2 REAL matrix [a, b; -b, a] whose trace + # as a REAL matrix will be 2*a = 2*Re(z_1). And so forth. + return (X*Y).trace()/cls.dimension_over_reals() - try: - # Works in QQ, AA, RDF, et cetera. - return tr.real() - except AttributeError: - # A quaternion doesn't have a real() method, but does - # have coefficient_tuple() method that returns the - # coefficients of 1, i, j, and k -- in that order. - return tr.coefficient_tuple()[0] - - -class RealMatrixEJA(MatrixEJA): - @staticmethod - def dimension_over_reals(): - return 1 - - -class RealSymmetricEJA(ConcreteEJA, RealMatrixEJA): +class RealSymmetricEJA(ConcreteEJA, RationalBasisEJA, MatrixEJA): """ The rank-n simple EJA consisting of real symmetric n-by-n matrices, the usual symmetric Jordan product, and the trace inner @@ -1848,13 +1845,13 @@ class RealSymmetricEJA(ConcreteEJA, RealMatrixEJA): EXAMPLES:: sage: J = RealSymmetricEJA(2) - sage: e0, e1, e2 = J.gens() - sage: e0*e0 - e0 - sage: e1*e1 - 1/2*e0 + 1/2*e2 - sage: e2*e2 - e2 + sage: b0, b1, b2 = J.gens() + sage: b0*b0 + b0 + sage: b1*b1 + 1/2*b0 + 1/2*b2 + sage: b2*b2 + b2 In theory, our "field" can be any subfield of the reals:: @@ -1901,7 +1898,7 @@ class RealSymmetricEJA(ConcreteEJA, RealMatrixEJA): """ @classmethod - def _denormalized_basis(cls, n): + def _denormalized_basis(cls, n, field): """ Return a basis for the space of real symmetric n-by-n matrices. @@ -1913,7 +1910,7 @@ class RealSymmetricEJA(ConcreteEJA, RealMatrixEJA): sage: set_random_seed() sage: n = ZZ.random_element(1,5) - sage: B = RealSymmetricEJA._denormalized_basis(n) + sage: B = RealSymmetricEJA._denormalized_basis(n,ZZ) sage: all( M.is_symmetric() for M in B) True @@ -1923,7 +1920,7 @@ class RealSymmetricEJA(ConcreteEJA, RealMatrixEJA): S = [] for i in range(n): for j in range(i+1): - Eij = matrix(ZZ, n, lambda k,l: k==i and l==j) + Eij = matrix(field, n, lambda k,l: k==i and l==j) if i == j: Sij = Eij else: @@ -1944,26 +1941,32 @@ class RealSymmetricEJA(ConcreteEJA, RealMatrixEJA): n = ZZ.random_element(cls._max_random_instance_size() + 1) return cls(n, **kwargs) - def __init__(self, n, **kwargs): + def __init__(self, n, field=AA, **kwargs): # We know this is a valid EJA, but will double-check # if the user passes check_axioms=True. if "check_axioms" not in kwargs: kwargs["check_axioms"] = False - super(RealSymmetricEJA, self).__init__(self._denormalized_basis(n), - self.jordan_product, - self.trace_inner_product, - **kwargs) + associative = False + if n <= 1: + associative = True + + super().__init__(self._denormalized_basis(n,field), + self.jordan_product, + self.trace_inner_product, + field=field, + associative=associative, + **kwargs) # TODO: this could be factored out somehow, but is left here # because the MatrixEJA is not presently a subclass of the # FDEJA class that defines rank() and one(). self.rank.set_cache(n) - idV = matrix.identity(ZZ, self.dimension_over_reals()*n) + idV = self.matrix_space().one() self.one.set_cache(self(idV)) -class ComplexMatrixEJA(MatrixEJA): +class ComplexMatrixEJA(RealEmbeddedMatrixEJA): # A manual dictionary-cache for the complex_extension() method, # since apparently @classmethods can't also be @cached_methods. _complex_extension = {} @@ -2042,7 +2045,7 @@ class ComplexMatrixEJA(MatrixEJA): True """ - super(ComplexMatrixEJA,cls).real_embed(M) + super().real_embed(M) n = M.nrows() # We don't need any adjoined elements... @@ -2089,7 +2092,7 @@ class ComplexMatrixEJA(MatrixEJA): True """ - super(ComplexMatrixEJA,cls).real_unembed(M) + super().real_unembed(M) n = ZZ(M.nrows()) d = cls.dimension_over_reals() F = cls.complex_extension(M.base_ring()) @@ -2111,7 +2114,7 @@ class ComplexMatrixEJA(MatrixEJA): return matrix(F, n/d, elements) -class ComplexHermitianEJA(ConcreteEJA, ComplexMatrixEJA): +class ComplexHermitianEJA(ConcreteEJA, RationalBasisEJA, ComplexMatrixEJA): """ The rank-n simple EJA consisting of complex Hermitian n-by-n matrices over the real numbers, the usual symmetric Jordan product, @@ -2170,7 +2173,7 @@ class ComplexHermitianEJA(ConcreteEJA, ComplexMatrixEJA): """ @classmethod - def _denormalized_basis(cls, n): + def _denormalized_basis(cls, n, field): """ Returns a basis for the space of complex Hermitian n-by-n matrices. @@ -2188,15 +2191,14 @@ class ComplexHermitianEJA(ConcreteEJA, ComplexMatrixEJA): sage: set_random_seed() sage: n = ZZ.random_element(1,5) - sage: B = ComplexHermitianEJA._denormalized_basis(n) + sage: B = ComplexHermitianEJA._denormalized_basis(n,ZZ) sage: all( M.is_symmetric() for M in B) True """ - field = ZZ - R = PolynomialRing(field, 'z') + R = PolynomialRing(ZZ, 'z') z = R.gen() - F = field.extension(z**2 + 1, 'I') + F = ZZ.extension(z**2 + 1, 'I') I = F.gen(1) # This is like the symmetric case, but we need to be careful: @@ -2227,20 +2229,26 @@ class ComplexHermitianEJA(ConcreteEJA, ComplexMatrixEJA): # "erase" E_ij Eij[i,j] = 0 - # Since we embedded these, we can drop back to the "field" that we - # started with instead of the complex extension "F". + # Since we embedded the entries, we can drop back to the + # desired real "field" instead of the extension "F". return tuple( s.change_ring(field) for s in S ) - def __init__(self, n, **kwargs): + def __init__(self, n, field=AA, **kwargs): # We know this is a valid EJA, but will double-check # if the user passes check_axioms=True. if "check_axioms" not in kwargs: kwargs["check_axioms"] = False - super(ComplexHermitianEJA, self).__init__(self._denormalized_basis(n), - self.jordan_product, - self.trace_inner_product, - **kwargs) + associative = False + if n <= 1: + associative = True + + super().__init__(self._denormalized_basis(n,field), + self.jordan_product, + self.trace_inner_product, + field=field, + associative=associative, + **kwargs) # TODO: this could be factored out somehow, but is left here # because the MatrixEJA is not presently a subclass of the # FDEJA class that defines rank() and one(). @@ -2260,7 +2268,7 @@ class ComplexHermitianEJA(ConcreteEJA, ComplexMatrixEJA): n = ZZ.random_element(cls._max_random_instance_size() + 1) return cls(n, **kwargs) -class QuaternionMatrixEJA(MatrixEJA): +class QuaternionMatrixEJA(RealEmbeddedMatrixEJA): # A manual dictionary-cache for the quaternion_extension() method, # since apparently @classmethods can't also be @cached_methods. @@ -2323,7 +2331,7 @@ class QuaternionMatrixEJA(MatrixEJA): True """ - super(QuaternionMatrixEJA,cls).real_embed(M) + super().real_embed(M) quaternions = M.base_ring() n = M.nrows() @@ -2378,7 +2386,7 @@ class QuaternionMatrixEJA(MatrixEJA): True """ - super(QuaternionMatrixEJA,cls).real_unembed(M) + super().real_unembed(M) n = ZZ(M.nrows()) d = cls.dimension_over_reals() @@ -2408,7 +2416,9 @@ class QuaternionMatrixEJA(MatrixEJA): return matrix(Q, n/d, elements) -class QuaternionHermitianEJA(ConcreteEJA, QuaternionMatrixEJA): +class QuaternionHermitianEJA(ConcreteEJA, + RationalBasisEJA, + QuaternionMatrixEJA): r""" The rank-n simple EJA consisting of self-adjoint n-by-n quaternion matrices, the usual symmetric Jordan product, and the @@ -2466,7 +2476,7 @@ class QuaternionHermitianEJA(ConcreteEJA, QuaternionMatrixEJA): """ @classmethod - def _denormalized_basis(cls, n): + def _denormalized_basis(cls, n, field): """ Returns a basis for the space of quaternion Hermitian n-by-n matrices. @@ -2484,12 +2494,11 @@ class QuaternionHermitianEJA(ConcreteEJA, QuaternionMatrixEJA): sage: set_random_seed() sage: n = ZZ.random_element(1,5) - sage: B = QuaternionHermitianEJA._denormalized_basis(n) + sage: B = QuaternionHermitianEJA._denormalized_basis(n,ZZ) sage: all( M.is_symmetric() for M in B ) True """ - field = ZZ Q = QuaternionAlgebra(QQ,-1,-1) I,J,K = Q.gens() @@ -2533,20 +2542,27 @@ class QuaternionHermitianEJA(ConcreteEJA, QuaternionMatrixEJA): # "erase" E_ij Eij[i,j] = 0 - # Since we embedded these, we can drop back to the "field" that we - # started with instead of the quaternion algebra "Q". + # Since we embedded the entries, we can drop back to the + # desired real "field" instead of the quaternion algebra "Q". return tuple( s.change_ring(field) for s in S ) - def __init__(self, n, **kwargs): + def __init__(self, n, field=AA, **kwargs): # We know this is a valid EJA, but will double-check # if the user passes check_axioms=True. if "check_axioms" not in kwargs: kwargs["check_axioms"] = False - super(QuaternionHermitianEJA, self).__init__(self._denormalized_basis(n), - self.jordan_product, - self.trace_inner_product, - **kwargs) + associative = False + if n <= 1: + associative = True + + super().__init__(self._denormalized_basis(n,field), + self.jordan_product, + self.trace_inner_product, + field=field, + associative=associative, + **kwargs) + # TODO: this could be factored out somehow, but is left here # because the MatrixEJA is not presently a subclass of the # FDEJA class that defines rank() and one(). @@ -2570,8 +2586,215 @@ class QuaternionHermitianEJA(ConcreteEJA, QuaternionMatrixEJA): n = ZZ.random_element(cls._max_random_instance_size() + 1) return cls(n, **kwargs) +class OctonionHermitianEJA(ConcreteEJA, MatrixEJA): + r""" + SETUP:: + + sage: from mjo.eja.eja_algebra import (FiniteDimensionalEJA, + ....: OctonionHermitianEJA) + + EXAMPLES: + + The 3-by-3 algebra satisfies the axioms of an EJA:: + + sage: OctonionHermitianEJA(3, # long time + ....: field=QQ, # long time + ....: orthonormalize=False, # long time + ....: check_axioms=True) # long time + Euclidean Jordan algebra of dimension 27 over Rational Field + + After a change-of-basis, the 2-by-2 algebra has the same + multiplication table as the ten-dimensional Jordan spin algebra:: + + sage: b = OctonionHermitianEJA._denormalized_basis(2,QQ) + sage: basis = (b[0] + b[9],) + b[1:9] + (b[0] - b[9],) + sage: jp = OctonionHermitianEJA.jordan_product + sage: ip = OctonionHermitianEJA.trace_inner_product + sage: J = FiniteDimensionalEJA(basis, + ....: jp, + ....: ip, + ....: field=QQ, + ....: orthonormalize=False) + sage: J.multiplication_table() + +----++----+----+----+----+----+----+----+----+----+----+ + | * || b0 | b1 | b2 | b3 | b4 | b5 | b6 | b7 | b8 | b9 | + +====++====+====+====+====+====+====+====+====+====+====+ + | b0 || b0 | b1 | b2 | b3 | b4 | b5 | b6 | b7 | b8 | b9 | + +----++----+----+----+----+----+----+----+----+----+----+ + | b1 || b1 | b0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | + +----++----+----+----+----+----+----+----+----+----+----+ + | b2 || b2 | 0 | b0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | + +----++----+----+----+----+----+----+----+----+----+----+ + | b3 || b3 | 0 | 0 | b0 | 0 | 0 | 0 | 0 | 0 | 0 | + +----++----+----+----+----+----+----+----+----+----+----+ + | b4 || b4 | 0 | 0 | 0 | b0 | 0 | 0 | 0 | 0 | 0 | + +----++----+----+----+----+----+----+----+----+----+----+ + | b5 || b5 | 0 | 0 | 0 | 0 | b0 | 0 | 0 | 0 | 0 | + +----++----+----+----+----+----+----+----+----+----+----+ + | b6 || b6 | 0 | 0 | 0 | 0 | 0 | b0 | 0 | 0 | 0 | + +----++----+----+----+----+----+----+----+----+----+----+ + | b7 || b7 | 0 | 0 | 0 | 0 | 0 | 0 | b0 | 0 | 0 | + +----++----+----+----+----+----+----+----+----+----+----+ + | b8 || b8 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | b0 | 0 | + +----++----+----+----+----+----+----+----+----+----+----+ + | b9 || b9 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | b0 | + +----++----+----+----+----+----+----+----+----+----+----+ + + TESTS: + + We can actually construct the 27-dimensional Albert algebra, + and we get the right unit element if we recompute it:: + + sage: J = OctonionHermitianEJA(3, # long time + ....: field=QQ, # long time + ....: orthonormalize=False) # long time + sage: J.one.clear_cache() # long time + sage: J.one() # long time + b0 + b9 + b26 + sage: J.one().to_matrix() # long time + +----+----+----+ + | e0 | 0 | 0 | + +----+----+----+ + | 0 | e0 | 0 | + +----+----+----+ + | 0 | 0 | e0 | + +----+----+----+ + + The 2-by-2 algebra is isomorphic to the ten-dimensional Jordan + spin algebra, but just to be sure, we recompute its rank:: + + sage: J = OctonionHermitianEJA(2, # long time + ....: field=QQ, # long time + ....: orthonormalize=False) # long time + sage: J.rank.clear_cache() # long time + sage: J.rank() # long time + 2 + + """ + @staticmethod + def _max_random_instance_size(): + r""" + The maximum rank of a random QuaternionHermitianEJA. + """ + return 1 # Dimension 1 + + @classmethod + def random_instance(cls, **kwargs): + """ + Return a random instance of this type of algebra. + """ + n = ZZ.random_element(cls._max_random_instance_size() + 1) + return cls(n, **kwargs) + + def __init__(self, n, field=AA, **kwargs): + if n > 3: + # Otherwise we don't get an EJA. + raise ValueError("n cannot exceed 3") + + # We know this is a valid EJA, but will double-check + # if the user passes check_axioms=True. + if "check_axioms" not in kwargs: kwargs["check_axioms"] = False + + super().__init__(self._denormalized_basis(n,field), + self.jordan_product, + self.trace_inner_product, + field=field, + **kwargs) + + # TODO: this could be factored out somehow, but is left here + # because the MatrixEJA is not presently a subclass of the + # FDEJA class that defines rank() and one(). + self.rank.set_cache(n) + idV = self.matrix_space().one() + self.one.set_cache(self(idV)) + + + @classmethod + def _denormalized_basis(cls, n, field): + """ + Returns a basis for the space of octonion Hermitian n-by-n + matrices. + + SETUP:: + + sage: from mjo.eja.eja_algebra import OctonionHermitianEJA + + EXAMPLES:: + + sage: B = OctonionHermitianEJA._denormalized_basis(3,QQ) + sage: all( M.is_hermitian() for M in B ) + True + sage: len(B) + 27 + + """ + from mjo.octonions import OctonionMatrixAlgebra + MS = OctonionMatrixAlgebra(n, scalars=field) + es = MS.entry_algebra().gens() + + basis = [] + for i in range(n): + for j in range(i+1): + if i == j: + E_ii = MS.monomial( (i,j,es[0]) ) + basis.append(E_ii) + else: + for e in es: + E_ij = MS.monomial( (i,j,e) ) + ec = e.conjugate() + # If the conjugate has a negative sign in front + # of it, (j,i,ec) won't be a monomial! + if (j,i,ec) in MS.indices(): + E_ij += MS.monomial( (j,i,ec) ) + else: + E_ij -= MS.monomial( (j,i,-ec) ) + basis.append(E_ij) + + return tuple( basis ) + + @staticmethod + def trace_inner_product(X,Y): + r""" + The octonions don't know that the reals are embedded in them, + so we have to take the e0 component ourselves. + + SETUP:: + + sage: from mjo.eja.eja_algebra import OctonionHermitianEJA + + TESTS:: + + sage: J = OctonionHermitianEJA(2,field=QQ,orthonormalize=False) + sage: I = J.one().to_matrix() + sage: J.trace_inner_product(I, -I) + -2 + + """ + return (X*Y).trace().real().coefficient(0) + + +class AlbertEJA(OctonionHermitianEJA): + r""" + The Albert algebra is the algebra of three-by-three Hermitian + matrices whose entries are octonions. + + SETUP:: + + from mjo.eja.eja_algebra import AlbertEJA + + EXAMPLES:: + + sage: AlbertEJA(field=QQ, orthonormalize=False) + Euclidean Jordan algebra of dimension 27 over Rational Field + sage: AlbertEJA() # long time + Euclidean Jordan algebra of dimension 27 over Algebraic Real Field -class HadamardEJA(ConcreteEJA): + """ + def __init__(self, *args, **kwargs): + super().__init__(3, *args, **kwargs) + + +class HadamardEJA(ConcreteEJA, RationalBasisEJA): """ Return the Euclidean Jordan Algebra corresponding to the set `R^n` under the Hadamard product. @@ -2589,19 +2812,19 @@ class HadamardEJA(ConcreteEJA): This multiplication table can be verified by hand:: sage: J = HadamardEJA(3) - sage: e0,e1,e2 = J.gens() - sage: e0*e0 - e0 - sage: e0*e1 + sage: b0,b1,b2 = J.gens() + sage: b0*b0 + b0 + sage: b0*b1 0 - sage: e0*e2 + sage: b0*b2 0 - sage: e1*e1 - e1 - sage: e1*e2 + sage: b1*b1 + b1 + sage: b1*b2 0 - sage: e2*e2 - e2 + sage: b2*b2 + b2 TESTS: @@ -2611,7 +2834,7 @@ class HadamardEJA(ConcreteEJA): (r0, r1, r2) """ - def __init__(self, n, **kwargs): + def __init__(self, n, field=AA, **kwargs): if n == 0: jordan_product = lambda x,y: x inner_product = lambda x,y: x @@ -2632,10 +2855,12 @@ class HadamardEJA(ConcreteEJA): if "orthonormalize" not in kwargs: kwargs["orthonormalize"] = False if "check_axioms" not in kwargs: kwargs["check_axioms"] = False - column_basis = tuple( b.column() for b in FreeModule(ZZ, n).basis() ) + column_basis = tuple( b.column() + for b in FreeModule(field, n).basis() ) super().__init__(column_basis, jordan_product, inner_product, + field=field, associative=True, **kwargs) self.rank.set_cache(n) @@ -2661,7 +2886,7 @@ class HadamardEJA(ConcreteEJA): return cls(n, **kwargs) -class BilinearFormEJA(ConcreteEJA): +class BilinearFormEJA(ConcreteEJA, RationalBasisEJA): r""" The rank-2 simple EJA consisting of real vectors ``x=(x0, x_bar)`` with the half-trace inner product and jordan product ``x*y = @@ -2743,7 +2968,7 @@ class BilinearFormEJA(ConcreteEJA): True """ - def __init__(self, B, **kwargs): + def __init__(self, B, field=AA, **kwargs): # The matrix "B" is supplied by the user in most cases, # so it makes sense to check whether or not its positive- # definite unless we are specifically asked not to... @@ -2771,11 +2996,20 @@ class BilinearFormEJA(ConcreteEJA): return P([z0] + zbar.list()) n = B.nrows() - column_basis = tuple( b.column() for b in FreeModule(ZZ, n).basis() ) - super(BilinearFormEJA, self).__init__(column_basis, - jordan_product, - inner_product, - **kwargs) + column_basis = tuple( b.column() + for b in FreeModule(field, n).basis() ) + + # TODO: I haven't actually checked this, but it seems legit. + associative = False + if n <= 2: + associative = True + + super().__init__(column_basis, + jordan_product, + inner_product, + field=field, + associative=associative, + **kwargs) # The rank of this algebra is two, unless we're in a # one-dimensional ambient space (because the rank is bounded @@ -2835,20 +3069,20 @@ class JordanSpinEJA(BilinearFormEJA): This multiplication table can be verified by hand:: sage: J = JordanSpinEJA(4) - sage: e0,e1,e2,e3 = J.gens() - sage: e0*e0 - e0 - sage: e0*e1 - e1 - sage: e0*e2 - e2 - sage: e0*e3 - e3 - sage: e1*e2 + sage: b0,b1,b2,b3 = J.gens() + sage: b0*b0 + b0 + sage: b0*b1 + b1 + sage: b0*b2 + b2 + sage: b0*b3 + b3 + sage: b1*b2 0 - sage: e1*e3 + sage: b1*b3 0 - sage: e2*e3 + sage: b2*b3 0 We can change the generator prefix:: @@ -2869,7 +3103,7 @@ class JordanSpinEJA(BilinearFormEJA): True """ - def __init__(self, n, **kwargs): + def __init__(self, n, *args, **kwargs): # This is a special case of the BilinearFormEJA with the # identity matrix as its bilinear form. B = matrix.identity(ZZ, n) @@ -2880,7 +3114,7 @@ class JordanSpinEJA(BilinearFormEJA): # But also don't pass check_field=False here, because the user # can pass in a field! - super(JordanSpinEJA, self).__init__(B, **kwargs) + super().__init__(B, *args, **kwargs) @staticmethod def _max_random_instance_size(): @@ -2900,7 +3134,7 @@ class JordanSpinEJA(BilinearFormEJA): return cls(n, **kwargs) -class TrivialEJA(ConcreteEJA): +class TrivialEJA(ConcreteEJA, RationalBasisEJA): """ The trivial Euclidean Jordan algebra consisting of only a zero element. @@ -2938,10 +3172,12 @@ class TrivialEJA(ConcreteEJA): if "orthonormalize" not in kwargs: kwargs["orthonormalize"] = False if "check_axioms" not in kwargs: kwargs["check_axioms"] = False - super(TrivialEJA, self).__init__(basis, - jordan_product, - inner_product, - **kwargs) + super().__init__(basis, + jordan_product, + inner_product, + associative=True, + **kwargs) + # The rank is zero using my definition, namely the dimension of the # largest subalgebra generated by any element. self.rank.set_cache(0) @@ -2954,8 +3190,7 @@ class TrivialEJA(ConcreteEJA): return cls(**kwargs) -class CartesianProductEJA(CombinatorialFreeModule_CartesianProduct, - FiniteDimensionalEJA): +class CartesianProductEJA(FiniteDimensionalEJA): r""" The external (orthogonal) direct sum of two or more Euclidean Jordan algebras. Every Euclidean Jordan algebra decomposes into an @@ -3051,6 +3286,33 @@ class CartesianProductEJA(CombinatorialFreeModule_CartesianProduct, sage: CP2.is_associative() False + Cartesian products of Cartesian products work:: + + sage: J1 = JordanSpinEJA(1) + sage: J2 = JordanSpinEJA(1) + sage: J3 = JordanSpinEJA(1) + sage: J = cartesian_product([J1,cartesian_product([J2,J3])]) + sage: J.multiplication_table() + +----++----+----+----+ + | * || b0 | b1 | b2 | + +====++====+====+====+ + | b0 || b0 | 0 | 0 | + +----++----+----+----+ + | b1 || 0 | b1 | 0 | + +----++----+----+----+ + | b2 || 0 | 0 | b2 | + +----++----+----+----+ + sage: HadamardEJA(3).multiplication_table() + +----++----+----+----+ + | * || b0 | b1 | b2 | + +====++====+====+====+ + | b0 || b0 | 0 | 0 | + +----++----+----+----+ + | b1 || 0 | b1 | 0 | + +----++----+----+----+ + | b2 || 0 | 0 | b2 | + +----++----+----+----+ + TESTS: All factors must share the same base field:: @@ -3078,37 +3340,41 @@ class CartesianProductEJA(CombinatorialFreeModule_CartesianProduct, Element = FiniteDimensionalEJAElement - def __init__(self, algebras, **kwargs): - CombinatorialFreeModule_CartesianProduct.__init__(self, - algebras, - **kwargs) - field = algebras[0].base_ring() - if not all( J.base_ring() == field for J in algebras ): + def __init__(self, factors, **kwargs): + m = len(factors) + if m == 0: + return TrivialEJA() + + self._sets = factors + + field = factors[0].base_ring() + if not all( J.base_ring() == field for J in factors ): raise ValueError("all factors must share the same base field") - associative = all( m.is_associative() for m in algebras ) + associative = all( f.is_associative() for f in factors ) - # The definition of matrix_space() and self.basis() relies - # only on the stuff in the CFM_CartesianProduct class, which - # we've already initialized. - Js = self.cartesian_factors() - m = len(Js) MS = self.matrix_space() - basis = tuple( - MS(tuple( self.cartesian_projection(i)(b).to_matrix() - for i in range(m) )) - for b in self.basis() - ) + basis = [] + zero = MS.zero() + for i in range(m): + for b in factors[i].matrix_basis(): + z = list(zero) + z[i] = b + basis.append(z) + + basis = tuple( MS(b) for b in basis ) # Define jordan/inner products that operate on that matrix_basis. def jordan_product(x,y): return MS(tuple( - (Js[i](x[i])*Js[i](y[i])).to_matrix() for i in range(m) + (factors[i](x[i])*factors[i](y[i])).to_matrix() + for i in range(m) )) def inner_product(x, y): return sum( - Js[i](x[i]).inner_product(Js[i](y[i])) for i in range(m) + factors[i](x[i]).inner_product(factors[i](y[i])) + for i in range(m) ) # There's no need to check the field since it already came @@ -3128,18 +3394,42 @@ class CartesianProductEJA(CombinatorialFreeModule_CartesianProduct, check_field=False, check_axioms=False) - ones = tuple(J.one() for J in algebras) - self.one.set_cache(self._cartesian_product_of_elements(ones)) - self.rank.set_cache(sum(J.rank() for J in algebras)) + ones = tuple(J.one().to_matrix() for J in factors) + self.one.set_cache(self(ones)) + self.rank.set_cache(sum(J.rank() for J in factors)) + + def cartesian_factors(self): + # Copy/pasted from CombinatorialFreeModule_CartesianProduct. + return self._sets + + def cartesian_factor(self, i): + r""" + Return the ``i``th factor of this algebra. + """ + return self._sets[i] + + def _repr_(self): + # Copy/pasted from CombinatorialFreeModule_CartesianProduct. + from sage.categories.cartesian_product import cartesian_product + return cartesian_product.symbol.join("%s" % factor + for factor in self._sets) def matrix_space(self): r""" Return the space that our matrix basis lives in as a Cartesian product. + We don't simply use the ``cartesian_product()`` functor here + because it acts differently on SageMath MatrixSpaces and our + custom MatrixAlgebras, which are CombinatorialFreeModules. We + always want the result to be represented (and indexed) as + an ordered tuple. + SETUP:: - sage: from mjo.eja.eja_algebra import (HadamardEJA, + sage: from mjo.eja.eja_algebra import (ComplexHermitianEJA, + ....: HadamardEJA, + ....: OctonionHermitianEJA, ....: RealSymmetricEJA) EXAMPLES:: @@ -3152,10 +3442,44 @@ class CartesianProductEJA(CombinatorialFreeModule_CartesianProduct, matrices over Algebraic Real Field, Full MatrixSpace of 2 by 2 dense matrices over Algebraic Real Field) + :: + + sage: J1 = ComplexHermitianEJA(1) + sage: J2 = ComplexHermitianEJA(1) + sage: J = cartesian_product([J1,J2]) + sage: J.one().to_matrix()[0] + [1 0] + [0 1] + sage: J.one().to_matrix()[1] + [1 0] + [0 1] + + :: + + sage: J1 = OctonionHermitianEJA(1) + sage: J2 = OctonionHermitianEJA(1) + sage: J = cartesian_product([J1,J2]) + sage: J.one().to_matrix()[0] + +----+ + | e0 | + +----+ + sage: J.one().to_matrix()[1] + +----+ + | e0 | + +----+ + """ - from sage.categories.cartesian_product import cartesian_product - return cartesian_product( [J.matrix_space() - for J in self.cartesian_factors()] ) + scalars = self.cartesian_factor(0).base_ring() + + # This category isn't perfect, but is good enough for what we + # need to do. + cat = MagmaticAlgebras(scalars).FiniteDimensional().WithBasis() + cat = cat.Unital().CartesianProducts() + factors = tuple( J.matrix_space() for J in self.cartesian_factors() ) + + from sage.sets.cartesian_product import CartesianProduct + return CartesianProduct(factors, cat) + @cached_method def cartesian_projection(self, i): @@ -3227,9 +3551,12 @@ class CartesianProductEJA(CombinatorialFreeModule_CartesianProduct, True """ - Ji = self.cartesian_factors()[i] - # Requires the fix on Trac 31421/31422 to work! - Pi = super().cartesian_projection(i) + offset = sum( self.cartesian_factor(k).dimension() + for k in range(i) ) + Ji = self.cartesian_factor(i) + Pi = self._module_morphism(lambda j: Ji.monomial(j - offset), + codomain=Ji) + return FiniteDimensionalEJAOperator(self,Ji,Pi.matrix()) @cached_method @@ -3335,9 +3662,11 @@ class CartesianProductEJA(CombinatorialFreeModule_CartesianProduct, True """ - Ji = self.cartesian_factors()[i] - # Requires the fix on Trac 31421/31422 to work! - Ei = super().cartesian_embedding(i) + offset = sum( self.cartesian_factor(k).dimension() + for k in range(i) ) + Ji = self.cartesian_factor(i) + Ei = Ji._module_morphism(lambda j: self.monomial(j + offset), + codomain=self) return FiniteDimensionalEJAOperator(Ji,self,Ei.matrix()) @@ -3352,7 +3681,9 @@ class RationalBasisCartesianProductEJA(CartesianProductEJA, SETUP:: - sage: from mjo.eja.eja_algebra import (JordanSpinEJA, + sage: from mjo.eja.eja_algebra import (HadamardEJA, + ....: JordanSpinEJA, + ....: OctonionHermitianEJA, ....: RealSymmetricEJA) EXAMPLES: @@ -3369,17 +3700,45 @@ class RationalBasisCartesianProductEJA(CartesianProductEJA, sage: J.rank() 5 + TESTS: + + The ``cartesian_product()`` function only uses the first factor to + decide where the result will live; thus we have to be careful to + check that all factors do indeed have a `_rational_algebra` member + before we try to access it:: + + sage: J1 = OctonionHermitianEJA(1) # no rational basis + sage: J2 = HadamardEJA(2) + sage: cartesian_product([J1,J2]) + Euclidean Jordan algebra of dimension 1 over Algebraic Real Field + (+) Euclidean Jordan algebra of dimension 2 over Algebraic Real Field + sage: cartesian_product([J2,J1]) + Euclidean Jordan algebra of dimension 2 over Algebraic Real Field + (+) Euclidean Jordan algebra of dimension 1 over Algebraic Real Field + """ def __init__(self, algebras, **kwargs): CartesianProductEJA.__init__(self, algebras, **kwargs) self._rational_algebra = None if self.vector_space().base_field() is not QQ: - self._rational_algebra = cartesian_product([ - r._rational_algebra for r in algebras - ]) + if all( hasattr(r, "_rational_algebra") for r in algebras ): + self._rational_algebra = cartesian_product([ + r._rational_algebra for r in algebras + ]) RationalBasisEJA.CartesianProduct = RationalBasisCartesianProductEJA -random_eja = ConcreteEJA.random_instance +def random_eja(*args, **kwargs): + J1 = ConcreteEJA.random_instance(*args, **kwargs) + + # This might make Cartesian products appear roughly as often as + # any other ConcreteEJA. + if ZZ.random_element(len(ConcreteEJA.__subclasses__()) + 1) == 0: + # Use random_eja() again so we can get more than two factors. + J2 = random_eja(*args, **kwargs) + J = cartesian_product([J1,J2]) + return J + else: + return J1