Integral lattices#

An integral lattice is a finitely generated free abelian group \(L \cong \ZZ^r\) equipped with a non-degenerate, symmetric bilinear form \(L \times L \colon \rightarrow \ZZ\).

Here, lattices have an ambient quadratic space \(\QQ^n\) and a distinguished basis.

EXAMPLES:

sage: M = Matrix(ZZ, [[0,1], [1,0]])
sage: IntegralLattice(M)
Lattice of degree 2 and rank 2 over Integer Ring
Standard basis
Inner product matrix:
[0 1]
[1 0]

A lattice can be defined by an inner product matrix of the ambient space and a basis:

sage: G = matrix.identity(3)
sage: basis = [[1,-1,0], [0,1,-1]]
sage: L = IntegralLattice(G, basis)
sage: L
Lattice of degree 3 and rank 2 over Integer Ring
Basis matrix:
[ 1 -1  0]
[ 0  1 -1]
Standard scalar product

sage: L.gram_matrix()
[ 2 -1]
[-1  2]

AUTHORS:

  • Simon Brandhorst (2017-09): First created

  • Paolo Menegatti (2018-03): Added IntegralLatticeDirectSum, IntegralLatticeGluing

class sage.modules.free_quadratic_module_integer_symmetric.FreeQuadraticModule_integer_symmetric(ambient, basis, inner_product_matrix, check=True, already_echelonized=False)#

Bases: FreeQuadraticModule_submodule_with_basis_pid

This class represents non-degenerate, integral, symmetric free quadratic \(\ZZ\)-modules.

INPUT:

  • ambient – an ambient free quadratic module

  • basis – a list of elements of ambient or a matrix

  • inner_product_matrix – a symmetric matrix over the rationals

EXAMPLES:

sage: IntegralLattice("U",basis=[vector([1,1])])
Lattice of degree 2 and rank 1 over Integer Ring
Basis matrix:
[1 1]
Inner product matrix:
[0 1]
[1 0]
LLL()#

Return this lattice with an LLL reduced basis.

EXAMPLES:

sage: L = IntegralLattice('A2')                                             # needs sage.graphs
sage: L.lll() == L                                                          # needs sage.graphs sage.libs.pari
True

sage: G = matrix(ZZ, 3, [0,1,0, 1,0,0, 0,0,7])
sage: V = matrix(ZZ, 3, [-14,-15,-15, -4,1,16, -5,-5,-4])
sage: L = IntegralLattice(V * G * V.T)
sage: L.lll().gram_matrix()                                                 # needs sage.libs.gap
[0 0 1]
[0 7 0]
[1 0 0]
automorphisms(gens=None, is_finite=None)#

Return the orthogonal group of this lattice as a matrix group.

The elements are isometries of the ambient vector space which preserve this lattice. They are represented by matrices with respect to the standard basis.

INPUT:

  • gens – a list of matrices (default:None)

  • is_finite – bool (default: None) If set to True, then the group is placed in the category of finite groups. Sage does not check this.

OUTPUT:

The matrix group generated by gens. If gens is not specified, then generators of the full orthogonal group of this lattice are computed. They are continued as the identity on the orthogonal complement of the lattice in its ambient space. Currently, we can only compute the orthogonal group for positive definite lattices.

EXAMPLES:

sage: A4 = IntegralLattice("A4")                                            # needs sage.graphs
sage: Aut = A4.orthogonal_group(); Aut                                      # needs sage.graphs sage.libs.gap
Group of isometries with 4 generators (
[0 0 0 1]  [-1 -1 -1  0]  [ 1  0  0  0]  [ 1  0  0  0]
[0 0 1 0]  [ 0  0  0 -1]  [-1 -1 -1 -1]  [ 0  1  0  0]
[0 1 0 0]  [ 0  0  1  1]  [ 0  0  0  1]  [ 0  0  1  1]
[1 0 0 0], [ 0  1  0  0], [ 0  0  1  0], [ 0  0  0 -1]
)

The group acts from the right on the lattice and its discriminant group:

sage: # needs sage.graphs sage.libs.gap
sage: x = A4.an_element()
sage: g = Aut.an_element(); g
[-1 -1 -1  0]
[ 0  0  1  0]
[ 0  0 -1 -1]
[ 0  1  1  1]
sage: x*g
(-1, -1, -1, 0)
sage: (x*g).parent() == A4
True
sage: (g*x).parent()
Vector space of dimension 4 over Rational Field
sage: y = A4.discriminant_group().an_element()
sage: y*g
(4)

If the group is finite we can compute the usual things:

sage: # needs sage.graphs sage.libs.gap
sage: Aut.order()
240
sage: conj = Aut.conjugacy_classes_representatives()
sage: len(conj)
14
sage: Aut.structure_description()
'C2 x S5'

The lattice can live in a larger ambient space:

sage: A2 = IntegralLattice(matrix.identity(3),
....:                      Matrix(ZZ, 2, 3, [1,-1,0,0,1,-1]))
sage: A2.orthogonal_group()                                                 # needs sage.libs.gap
Group of isometries with 2 generators (
[ 2/3  2/3 -1/3]  [1 0 0]
[ 2/3 -1/3  2/3]  [0 0 1]
[-1/3  2/3  2/3], [0 1 0]
)

It can be negative definite as well:

sage: A2m = IntegralLattice(-Matrix(ZZ, 2, [2,1,1,2]))
sage: G = A2m.orthogonal_group()                                            # needs sage.libs.gap
sage: G.order()                                                             # needs sage.libs.gap
12

If the lattice is indefinite, sage does not know how to compute generators. Can you teach it?:

sage: U = IntegralLattice(Matrix(ZZ, 2, [0,1,1,0]))
sage: U.orthogonal_group()                                                  # needs sage.libs.gap
Traceback (most recent call last):
...
NotImplementedError: currently, we can only compute generators
for orthogonal groups over definite lattices.

But we can define subgroups:

sage: S = IntegralLattice(Matrix(ZZ, 2, [2, 3, 3, 2]))
sage: f = Matrix(ZZ, 2, [0,1,-1,3])
sage: S.orthogonal_group([f])                                               # needs sage.libs.gap
Group of isometries with 1 generator (
[ 0  1]
[-1  3]
)
direct_sum(M)#

Return the direct sum of this lattice with M.

INPUT:

  • M – a module over \(\ZZ\)

EXAMPLES:

sage: A = IntegralLattice(1)
sage: A.direct_sum(A)
Lattice of degree 2 and rank 2 over Integer Ring
Standard basis
Standard scalar product
discriminant_group(s=0)#

Return the discriminant group \(L^\vee / L\) of this lattice.

INPUT:

  • s – an integer (default: 0)

OUTPUT:

The \(s\) primary part of the discriminant group. If \(s=0\), returns the whole discriminant group.

EXAMPLES:

sage: L = IntegralLattice(Matrix(ZZ, 2, 2, [2,1,1,-2]) * 2)
sage: L.discriminant_group()
Finite quadratic module over Integer Ring with invariants (2, 10)
Gram matrix of the quadratic form with values in Q/2Z:
[  1 1/2]
[1/2 1/5]
sage: L.discriminant_group(2)
Finite quadratic module over Integer Ring with invariants (2, 2)
Gram matrix of the quadratic form with values in Q/2Z:
[  1 1/2]
[1/2   1]
sage: L.discriminant_group(5)
Finite quadratic module over Integer Ring with invariants (5,)
Gram matrix of the quadratic form with values in Q/2Z:
[4/5]
dual_lattice()#

Return the dual lattice as a FreeQuadraticModule

Let \(L\) be a lattice. Its dual lattice is

\[L^\vee = \{x \in L \otimes \QQ : (x, l) \in \ZZ \; \forall l \in L \}.\]

EXAMPLES:

sage: L = IntegralLattice("A2")                                             # needs sage.graphs
sage: Ldual = L.dual_lattice(); Ldual                                       # needs sage.graphs
Free module of degree 2 and rank 2 over Integer Ring
Echelon basis matrix:
[1/3 2/3]
[  0   1]

Since our lattices are always integral, a lattice is contained in its dual:

sage: L.is_submodule(Ldual)                                                 # needs sage.graphs
True
genus()#

Return the genus of this lattice.

EXAMPLES:

sage: L = IntegralLattice("U")
sage: L.genus()                                                             # needs sage.padics
Genus of
[0 1]
[1 0]
Signature:  (1, 1)
Genus symbol at 2:    1^2
is_even()#

Return whether the diagonal entries of the Gram matrix are even.

EXAMPLES:

sage: G = Matrix(ZZ, 2, 2, [-1,1,1,2])
sage: L = IntegralLattice(G)
sage: L.is_even()
False
sage: L = IntegralLattice("A2")                                             # needs sage.graphs
sage: L.is_even()                                                           # needs sage.graphs
True
is_primitive(M)#

Return whether M is a primitive submodule of this lattice.

A \(\ZZ\)-submodule M of a \(\ZZ\)-module L is called primitive if the quotient L/M is torsion free.

INPUT:

  • M – a submodule of this lattice

EXAMPLES:

sage: U = IntegralLattice("U")
sage: L1 = U.span([vector([1,1])])
sage: L2 = U.span([vector([1,-1])])
sage: U.is_primitive(L1)
True
sage: U.is_primitive(L2)
True
sage: U.is_primitive(L1 + L2)
False

We can also compute the index:

sage: (L1 + L2).index_in(U)
2
lll()#

Return this lattice with an LLL reduced basis.

EXAMPLES:

sage: L = IntegralLattice('A2')                                             # needs sage.graphs
sage: L.lll() == L                                                          # needs sage.graphs sage.libs.pari
True

sage: G = matrix(ZZ, 3, [0,1,0, 1,0,0, 0,0,7])
sage: V = matrix(ZZ, 3, [-14,-15,-15, -4,1,16, -5,-5,-4])
sage: L = IntegralLattice(V * G * V.T)
sage: L.lll().gram_matrix()                                                 # needs sage.libs.gap
[0 0 1]
[0 7 0]
[1 0 0]
max()#

Return the maximum of this lattice.

\[\max\{x^2 | x \in L\setminus \{0\}\}\]

EXAMPLES:

sage: L = IntegralLattice('A2')                                             # needs sage.graphs
sage: L.maximum()                                                           # needs sage.graphs
+Infinity
sage: L.twist(-1).maximum()                                                 # needs sage.graphs sage.libs.pari
-2
maximal_overlattice(p=None)#

Return a maximal even integral overlattice of this lattice.

INPUT:

  • p – (default:None) if given return an overlattice \(M\) of this lattice \(L\) that is maximal at \(p\) and the completions \(M_q = L_q\) are equal for all primes \(q \neq p\).

If \(p\) is \(2\) or None, then the lattice must be even.

EXAMPLES:

sage: # needs sage.graphs sage.libs.pari
sage: L = IntegralLattice("A4").twist(25*89)
sage: L.maximal_overlattice().determinant()
5
sage: L.maximal_overlattice(89).determinant().factor()
5^9
sage: L.maximal_overlattice(5).determinant().factor()
5 * 89^4
maximum()#

Return the maximum of this lattice.

\[\max\{x^2 | x \in L\setminus \{0\}\}\]

EXAMPLES:

sage: L = IntegralLattice('A2')                                             # needs sage.graphs
sage: L.maximum()                                                           # needs sage.graphs
+Infinity
sage: L.twist(-1).maximum()                                                 # needs sage.graphs sage.libs.pari
-2
min()#

Return the minimum of this lattice.

\[\min\{x^2 | x \in L\setminus \{0\}\}\]

EXAMPLES:

sage: L = IntegralLattice('A2')                                             # needs sage.graphs
sage: L.minimum()                                                           # needs sage.graphs
2
sage: L.twist(-1).minimum()                                                 # needs sage.graphs
-Infinity
minimum()#

Return the minimum of this lattice.

\[\min\{x^2 | x \in L\setminus \{0\}\}\]

EXAMPLES:

sage: L = IntegralLattice('A2')                                             # needs sage.graphs
sage: L.minimum()                                                           # needs sage.graphs
2
sage: L.twist(-1).minimum()                                                 # needs sage.graphs
-Infinity
orthogonal_complement(M)#

Return the orthogonal complement of M in this lattice.

INPUT:

  • M – a module in the same ambient space or a list of elements of the ambient space

EXAMPLES:

sage: H5 = Matrix(ZZ, 2, [2,1,1,-2])
sage: L = IntegralLattice(H5)
sage: S = L.span([vector([1,1])])
sage: L.orthogonal_complement(S)
Lattice of degree 2 and rank 1 over Integer Ring
Basis matrix:
[1 3]
Inner product matrix:
[ 2  1]
[ 1 -2]

sage: L = IntegralLattice(2)
sage: L.orthogonal_complement([vector(ZZ, [1,0])])
Lattice of degree 2 and rank 1 over Integer Ring
Basis matrix:
[0 1]
Standard scalar product
orthogonal_group(gens=None, is_finite=None)#

Return the orthogonal group of this lattice as a matrix group.

The elements are isometries of the ambient vector space which preserve this lattice. They are represented by matrices with respect to the standard basis.

INPUT:

  • gens – a list of matrices (default:None)

  • is_finite – bool (default: None) If set to True, then the group is placed in the category of finite groups. Sage does not check this.

OUTPUT:

The matrix group generated by gens. If gens is not specified, then generators of the full orthogonal group of this lattice are computed. They are continued as the identity on the orthogonal complement of the lattice in its ambient space. Currently, we can only compute the orthogonal group for positive definite lattices.

EXAMPLES:

sage: A4 = IntegralLattice("A4")                                            # needs sage.graphs
sage: Aut = A4.orthogonal_group(); Aut                                      # needs sage.graphs sage.libs.gap
Group of isometries with 4 generators (
[0 0 0 1]  [-1 -1 -1  0]  [ 1  0  0  0]  [ 1  0  0  0]
[0 0 1 0]  [ 0  0  0 -1]  [-1 -1 -1 -1]  [ 0  1  0  0]
[0 1 0 0]  [ 0  0  1  1]  [ 0  0  0  1]  [ 0  0  1  1]
[1 0 0 0], [ 0  1  0  0], [ 0  0  1  0], [ 0  0  0 -1]
)

The group acts from the right on the lattice and its discriminant group:

sage: # needs sage.graphs sage.libs.gap
sage: x = A4.an_element()
sage: g = Aut.an_element(); g
[-1 -1 -1  0]
[ 0  0  1  0]
[ 0  0 -1 -1]
[ 0  1  1  1]
sage: x*g
(-1, -1, -1, 0)
sage: (x*g).parent() == A4
True
sage: (g*x).parent()
Vector space of dimension 4 over Rational Field
sage: y = A4.discriminant_group().an_element()
sage: y*g
(4)

If the group is finite we can compute the usual things:

sage: # needs sage.graphs sage.libs.gap
sage: Aut.order()
240
sage: conj = Aut.conjugacy_classes_representatives()
sage: len(conj)
14
sage: Aut.structure_description()
'C2 x S5'

The lattice can live in a larger ambient space:

sage: A2 = IntegralLattice(matrix.identity(3),
....:                      Matrix(ZZ, 2, 3, [1,-1,0,0,1,-1]))
sage: A2.orthogonal_group()                                                 # needs sage.libs.gap
Group of isometries with 2 generators (
[ 2/3  2/3 -1/3]  [1 0 0]
[ 2/3 -1/3  2/3]  [0 0 1]
[-1/3  2/3  2/3], [0 1 0]
)

It can be negative definite as well:

sage: A2m = IntegralLattice(-Matrix(ZZ, 2, [2,1,1,2]))
sage: G = A2m.orthogonal_group()                                            # needs sage.libs.gap
sage: G.order()                                                             # needs sage.libs.gap
12

If the lattice is indefinite, sage does not know how to compute generators. Can you teach it?:

sage: U = IntegralLattice(Matrix(ZZ, 2, [0,1,1,0]))
sage: U.orthogonal_group()                                                  # needs sage.libs.gap
Traceback (most recent call last):
...
NotImplementedError: currently, we can only compute generators
for orthogonal groups over definite lattices.

But we can define subgroups:

sage: S = IntegralLattice(Matrix(ZZ, 2, [2, 3, 3, 2]))
sage: f = Matrix(ZZ, 2, [0,1,-1,3])
sage: S.orthogonal_group([f])                                               # needs sage.libs.gap
Group of isometries with 1 generator (
[ 0  1]
[-1  3]
)
overlattice(gens)#

Return the lattice spanned by this lattice and gens.

INPUT:

  • gens – a list of elements or a rational matrix

EXAMPLES:

sage: L = IntegralLattice(Matrix(ZZ, 2, 2, [2,0,0,2]))
sage: M = L.overlattice([vector([1,1])/2])
sage: M.gram_matrix()
[1 1]
[1 2]
quadratic_form()#

Return the quadratic form given by \(q(x)=(x,x)\).

EXAMPLES:

sage: L = IntegralLattice("A2")                                             # needs sage.graphs
sage: q = L.quadratic_form(); q                                             # needs sage.graphs
Quadratic form in 2 variables over Integer Ring with coefficients:
[ 2 -2 ]
[ * 2 ]
short_vectors(n, **kwargs)#

Return the short vectors of length \(< n\).

INPUT:

  • n – an integer

  • further keyword arguments are passed on to sage.quadratic_forms.short_vector_list_up_to_length().

OUTPUT:

  • a list \(L\) where L[k] is the list of vectors of lengths \(k\)

EXAMPLES:

sage: A2 = IntegralLattice('A2')                                            # needs sage.graphs
sage: A2.short_vectors(3)                                                   # needs sage.graphs sage.libs.pari
[[(0, 0)], [], [(1, 1), (-1, -1), (0, 1), (0, -1), (1, 0), (-1, 0)]]
sage: A2.short_vectors(3, up_to_sign_flag=True)                             # needs sage.graphs sage.libs.pari
[[(0, 0)], [], [(1, 1), (0, 1), (1, 0)]]
signature()#

Return the signature of this lattice, which is defined as the difference between the number of positive eigenvalues and the number of negative eigenvalues in the Gram matrix.

EXAMPLES:

sage: U = IntegralLattice("U")
sage: U.signature()
0
signature_pair()#

Return the signature tuple \((n_+,n_-)\) of this lattice.

Here \(n_+\) (resp. \(n_-\)) is the number of positive (resp. negative) eigenvalues of the Gram matrix.

EXAMPLES:

sage: A2 = IntegralLattice("A2")                                            # needs sage.graphs
sage: A2.signature_pair()                                                   # needs sage.graphs
(2, 0)
sublattice(basis)#

Return the sublattice spanned by basis.

INPUT:

  • basis – A list of elements of this lattice.

EXAMPLES:

sage: U = IntegralLattice("U")
sage: S = U.sublattice([vector([1,1])]); S
Lattice of degree 2 and rank 1 over Integer Ring
Basis matrix:
[1 1]
Inner product matrix:
[0 1]
[1 0]
sage: U.sublattice([vector([1,-1])/2])
Traceback (most recent call last):
...
ValueError: lattices must be integral; use FreeQuadraticModule instead
sage: S.sublattice([vector([1,-1])])
Traceback (most recent call last):
...
ValueError: the basis (= [(1, -1)]) does not span a submodule
tensor_product(other, discard_basis=False)#

Return the tensor product of self and other.

INPUT:

  • other – an integral lattice

  • discard_basis – a boolean (default: False). If True, then the lattice returned is equipped with the standard basis.

EXAMPLES:

sage: # needs sage.graphs
sage: L = IntegralLattice("D3", [[1,-1,0], [0,1,-1]])
sage: L1 = L.tensor_product(L); L1
Lattice of degree 9 and rank 4 over Integer Ring
Basis matrix:
[ 1 -1  0 -1  1  0  0  0  0]
[ 0  1 -1  0 -1  1  0  0  0]
[ 0  0  0  1 -1  0 -1  1  0]
[ 0  0  0  0  1 -1  0 -1  1]
Inner product matrix:
[ 4 -2 -2 -2  1  1 -2  1  1]
[-2  4  0  1 -2  0  1 -2  0]
[-2  0  4  1  0 -2  1  0 -2]
[-2  1  1  4 -2 -2  0  0  0]
[ 1 -2  0 -2  4  0  0  0  0]
[ 1  0 -2 -2  0  4  0  0  0]
[-2  1  1  0  0  0  4 -2 -2]
[ 1 -2  0  0  0  0 -2  4  0]
[ 1  0 -2  0  0  0 -2  0  4]
sage: L1.gram_matrix()
[ 36 -12 -12   4]
[-12  24   4  -8]
[-12   4  24  -8]
[  4  -8  -8  16]
sage: L2 = L.tensor_product(L, True); L2
Lattice of degree 4 and rank 4 over Integer Ring
Standard basis
Inner product matrix:
[ 36 -12 -12   4]
[-12  24   4  -8]
[-12   4  24  -8]
[  4  -8  -8  16]
twist(s, discard_basis=False)#

Return the lattice with inner product matrix scaled by s.

INPUT:

  • s – a nonzero integer

  • discard_basis – a boolean (default: False). If True, then the lattice returned is equipped with the standard basis.

EXAMPLES:

sage: L = IntegralLattice("A4")                                             # needs sage.graphs
sage: L.twist(3)                                                            # needs sage.graphs
Lattice of degree 4 and rank 4 over Integer Ring
Standard basis
Inner product matrix:
[ 6 -3  0  0]
[-3  6 -3  0]
[ 0 -3  6 -3]
[ 0  0 -3  6]
sage: L = IntegralLattice(3, [[2,1,0], [0,1,1]]); L
Lattice of degree 3 and rank 2 over Integer Ring
Basis matrix:
[2 1 0]
[0 1 1]
Standard scalar product
sage: L.twist(1)
Lattice of degree 3 and rank 2 over Integer Ring
Basis matrix:
[2 1 0]
[0 1 1]
Standard scalar product
sage: L.twist(1, True)
Lattice of degree 2 and rank 2 over Integer Ring
Standard basis
Inner product matrix:
[5 1]
[1 2]
sage.modules.free_quadratic_module_integer_symmetric.IntegralLattice(data, basis=None)#

Return the integral lattice spanned by basis in the ambient space.

A lattice is a finitely generated free abelian group \(L \cong \ZZ^r\) equipped with a non-degenerate, symmetric bilinear form \(L \times L \colon \rightarrow \ZZ\). Here, lattices have an ambient quadratic space \(\QQ^n\) and a distinguished basis.

INPUT:

The input is a descriptor of the lattice and a (optional) basis. - data – can be one of the following:

  • a symmetric matrix over the rationals – the inner product matrix

  • an integer – the dimension for an Euclidean lattice

  • a symmetric Cartan type or anything recognized by CartanMatrix (see also Cartan types) – for a root lattice

  • the string "U" or "H" – for hyperbolic lattices

  • basis – (optional) a matrix whose rows form a basis of the lattice, or a list of module elements forming a basis

OUTPUT:

A lattice in the ambient space defined by the inner_product_matrix. Unless specified, the basis of the lattice is the standard basis.

EXAMPLES:

sage: H5 = Matrix(ZZ, 2, [2,1,1,-2])
sage: IntegralLattice(H5)
Lattice of degree 2 and rank 2 over Integer Ring
Standard basis
Inner product matrix:
[ 2  1]
[ 1 -2]

A basis can be specified too:

sage: IntegralLattice(H5, Matrix([1,1]))
Lattice of degree 2 and rank 1 over Integer Ring
Basis matrix:
[1 1]
Inner product matrix:
[ 2  1]
[ 1 -2]

We can define an Euclidean lattice just by its dimension:

sage: IntegralLattice(3)
Lattice of degree 3 and rank 3 over Integer Ring
Standard basis
Standard scalar product

Here is an example of the \(A_2\) root lattice in Euclidean space:

sage: basis = Matrix([[1,-1,0], [0,1,-1]])
sage: A2 = IntegralLattice(3, basis)
sage: A2
Lattice of degree 3 and rank 2 over Integer Ring
Basis matrix:
[ 1 -1  0]
[ 0  1 -1]
Standard scalar product
sage: A2.gram_matrix()
[ 2 -1]
[-1  2]

We use "U" or "H" for defining a hyperbolic lattice:

sage: L1 = IntegralLattice("U")
sage: L1
Lattice of degree 2 and rank 2 over Integer Ring
Standard basis
Inner product matrix:
[0 1]
[1 0]
sage: L1 == IntegralLattice("H")
True

We can construct root lattices by specifying their type (see Cartan types and CartanMatrix):

sage: # needs sage.graphs
sage: IntegralLattice(["E", 7])
Lattice of degree 7 and rank 7 over Integer Ring
Standard basis
Inner product matrix:
[ 2  0 -1  0  0  0  0]
[ 0  2  0 -1  0  0  0]
[-1  0  2 -1  0  0  0]
[ 0 -1 -1  2 -1  0  0]
[ 0  0  0 -1  2 -1  0]
[ 0  0  0  0 -1  2 -1]
[ 0  0  0  0  0 -1  2]
sage: IntegralLattice(["A", 2])
Lattice of degree 2 and rank 2 over Integer Ring
Standard basis
Inner product matrix:
[ 2 -1]
[-1  2]
sage: IntegralLattice("D3")
Lattice of degree 3 and rank 3 over Integer Ring
Standard basis
Inner product matrix:
[ 2 -1 -1]
[-1  2  0]
[-1  0  2]
sage: IntegralLattice(["D", 4])
Lattice of degree 4 and rank 4 over Integer Ring
Standard basis
Inner product matrix:
[ 2 -1  0  0]
[-1  2 -1 -1]
[ 0 -1  2  0]
[ 0 -1  0  2]

We can specify a basis as well:

sage: G = Matrix(ZZ, 2, [0,1,1,0])
sage: B = [vector([1,1])]
sage: IntegralLattice(G, basis=B)
Lattice of degree 2 and rank 1 over Integer Ring
Basis matrix:
[1 1]
Inner product matrix:
[0 1]
[1 0]
sage: IntegralLattice(["A", 3], [[1,1,1]])                                      # needs sage.graphs
Lattice of degree 3 and rank 1 over Integer Ring
Basis matrix:
[1 1 1]
Inner product matrix:
[ 2 -1  0]
[-1  2 -1]
[ 0 -1  2]
sage: IntegralLattice(4, [[1,1,1,1]])
Lattice of degree 4 and rank 1 over Integer Ring
Basis matrix:
[1 1 1 1]
Standard scalar product
sage: IntegralLattice("A2", [[1,1]])                                            # needs sage.graphs
Lattice of degree 2 and rank 1 over Integer Ring
Basis matrix:
[1 1]
Inner product matrix:
[ 2 -1]
[-1  2]
sage.modules.free_quadratic_module_integer_symmetric.IntegralLatticeDirectSum(Lattices, return_embeddings=False)#

Return the direct sum of the lattices contained in the list Lattices.

INPUT:

  • Lattices – a list of lattices [L_1,...,L_n]

  • return_embeddings – (default: False) a boolean

OUTPUT:

The direct sum of the \(L_i\) if return_embeddings is False or the tuple [L, phi] where \(L\) is the direct sum of \(L_i\) and phi is the list of embeddings from \(L_i\) to \(L\).

EXAMPLES:

sage: # needs sage.graphs
sage: from sage.modules.free_quadratic_module_integer_symmetric import IntegralLatticeDirectSum
sage: L1 = IntegralLattice("D4")
sage: L2 = IntegralLattice("A3", [[1, 1, 2]])
sage: L3 = IntegralLattice("A4", [[0, 1, 1, 2], [1, 2, 3, 1]])
sage: Lattices = [L1, L2, L3]
sage: IntegralLatticeDirectSum([L1, L2, L3])
Lattice of degree 11 and rank 7 over Integer Ring
Basis matrix:
[1 0 0 0 0 0 0 0 0 0 0]
[0 1 0 0 0 0 0 0 0 0 0]
[0 0 1 0 0 0 0 0 0 0 0]
[0 0 0 1 0 0 0 0 0 0 0]
[0 0 0 0 1 1 2 0 0 0 0]
[0 0 0 0 0 0 0 0 1 1 2]
[0 0 0 0 0 0 0 1 2 3 1]
Inner product matrix:
[ 2 -1  0  0  0  0  0  0  0  0  0]
[-1  2 -1 -1  0  0  0  0  0  0  0]
[ 0 -1  2  0  0  0  0  0  0  0  0]
[ 0 -1  0  2  0  0  0  0  0  0  0]
[ 0  0  0  0  2 -1  0  0  0  0  0]
[ 0  0  0  0 -1  2 -1  0  0  0  0]
[ 0  0  0  0  0 -1  2  0  0  0  0]
[ 0  0  0  0  0  0  0  2 -1  0  0]
[ 0  0  0  0  0  0  0 -1  2 -1  0]
[ 0  0  0  0  0  0  0  0 -1  2 -1]
[ 0  0  0  0  0  0  0  0  0 -1  2]
sage: [L, phi] = IntegralLatticeDirectSum([L1, L2, L3], True)
sage: LL3 = L.sublattice(phi[2].image().basis_matrix())
sage: L3.discriminant() == LL3.discriminant()
True
sage: x = L3([1, 2, 3, 1])
sage: phi[2](x).inner_product(phi[2](x)) == x.inner_product(x)
True
sage.modules.free_quadratic_module_integer_symmetric.IntegralLatticeGluing(Lattices, glue, return_embeddings=False)#

Return an overlattice of the direct sum as defined by glue.

INPUT:

  • Lattices – a list of lattices \([L_1,...,L_n]\)

  • glue – a list where the elements are lists in the form \([g_1,...,g_n]\); here \(g_i\) is an element of the discriminant group of \(L_i`and the overlattice is spanned by the additional ``[sum(g) for g in glue]`\)

  • return_embeddings – (default: False) a boolean

OUTPUT:

The glued lattice given by \(L_i\) and glue if return_embeddings is False or the tuple [L, phi] where \(L\) is the glued lattice and phi the list of embeddings from \(L_i\) to \(L\)

EXAMPLES:

A single lattice can be glued. This is the same as taking an overlattice:

sage: from sage.modules.free_quadratic_module_integer_symmetric import IntegralLatticeGluing
sage: L1 = IntegralLattice(matrix([[4]]))
sage: g1 = L1.discriminant_group().gens()[0]
sage: glue = [[2 * g1]]
sage: L = IntegralLatticeGluing([L1], glue)
sage: L
Lattice of degree 1 and rank 1 over Integer Ring
Basis matrix:
[1/2]
Inner product matrix:
[4]
sage: L.gram_matrix()
[1]
sage: IntegralLatticeGluing([L1], glue, return_embeddings=True)
[Lattice of degree 1 and rank 1 over Integer Ring
 Basis matrix:
 [1/2]
 Inner product matrix:
 [4], [Free module morphism defined by the matrix
  [2]
  Domain: Lattice of degree 1 and rank 1 over Integer Ring
  Standard basis
  Inner product matrix:
  [4]
  Codomain: Lattice of degree 1 and rank 1 over Integer Ring
  Basis matrix:
  [1/2]
  Inner product matrix:
  [4]]]

sage: # needs sage.graphs
sage: L1 = IntegralLattice([[2]])
sage: L2 = IntegralLattice([[2]])
sage: AL1 = L1.discriminant_group()
sage: AL2 = L2.discriminant_group()
sage: AL1
Finite quadratic module over Integer Ring with invariants (2,)
Gram matrix of the quadratic form with values in Q/2Z:
[1/2]
sage: g1 = L1.discriminant_group().gens()[0]
sage: g2 = L2.discriminant_group().gens()[0]
sage: glue = [[g1, g2]]
sage: IntegralLatticeGluing([L1, L2], glue)
Lattice of degree 2 and rank 2 over Integer Ring
Basis matrix:
[1/2 1/2]
[  0   1]
Inner product matrix:
[2 0]
[0 2]

sage: # needs sage.graphs
sage: L1 = IntegralLattice("A4")
sage: L2 = IntegralLattice("A4")
sage: g1 = L1.discriminant_group().gens()[0]
sage: g2 = L2.discriminant_group().gens()[0]
sage: glue = [[g1, 2 * g2]]
sage: [V, phi] = IntegralLatticeGluing([L1, L2], glue, True)
sage: V
Lattice of degree 8 and rank 8 over Integer Ring
Basis matrix:
[1/5 2/5 3/5 4/5 2/5 4/5 1/5 3/5]
[  0   1   0   0   0   0   0   0]
[  0   0   1   0   0   0   0   0]
[  0   0   0   1   0   0   0   0]
[  0   0   0   0   1   0   0   0]
[  0   0   0   0   0   1   0   0]
[  0   0   0   0   0   0   1   0]
[  0   0   0   0   0   0   0   1]
Inner product matrix:
[ 2 -1  0  0  0  0  0  0]
[-1  2 -1  0  0  0  0  0]
[ 0 -1  2 -1  0  0  0  0]
[ 0  0 -1  2  0  0  0  0]
[ 0  0  0  0  2 -1  0  0]
[ 0  0  0  0 -1  2 -1  0]
[ 0  0  0  0  0 -1  2 -1]
[ 0  0  0  0  0  0 -1  2]
sage: V.sublattice(phi[0].image().basis_matrix())
Lattice of degree 8 and rank 4 over Integer Ring
Basis matrix:
[1 0 0 0 0 0 0 0]
[0 1 0 0 0 0 0 0]
[0 0 1 0 0 0 0 0]
[0 0 0 1 0 0 0 0]
Inner product matrix:
[ 2 -1  0  0  0  0  0  0]
[-1  2 -1  0  0  0  0  0]
[ 0 -1  2 -1  0  0  0  0]
[ 0  0 -1  2  0  0  0  0]
[ 0  0  0  0  2 -1  0  0]
[ 0  0  0  0 -1  2 -1  0]
[ 0  0  0  0  0 -1  2 -1]
[ 0  0  0  0  0  0 -1  2]

Different gluings can be composed:

sage: # needs sage.graphs
sage: D4 = IntegralLattice("D4")
sage: D4.discriminant_group()
Finite quadratic module over Integer Ring with invariants (2, 2)
Gram matrix of the quadratic form with values in Q/2Z:
[  1 1/2]
[1/2   1]
sage: L2 = IntegralLattice(2 * matrix.identity(2))
sage: L2.discriminant_group()
Finite quadratic module over Integer Ring with invariants (2, 2)
Gram matrix of the quadratic form with values in Q/2Z:
[1/2   0]
[  0 1/2]
sage: g1 = D4.discriminant_group().gens()[0]
sage: g2 = L2.discriminant_group().gens()[0] + L2.discriminant_group().gens()[1]
sage: D6, phi = IntegralLatticeGluing([D4, L2], [[g1, g2]], True)
sage: AD6 = D6.discriminant_group()
sage: AD6.normal_form()
Finite quadratic module over Integer Ring with invariants (2, 2)
Gram matrix of the quadratic form with values in Q/2Z:
[3/2   0]
[  0 3/2]
sage: f1, g1 = AD6.normal_form().gens()
sage: f2, g2 = L2.discriminant_group().gens()
sage: E8, psi = IntegralLatticeGluing([D6, L2], [[f1, f2], [g1, g2]], True)
sage: D4embed = E8.sublattice(psi[0](phi[0].image()).basis_matrix())
sage: x = D4([1, 0, 0, 0])
sage: psi[0](phi[0](x)).inner_product(psi[0](phi[0](x))) == x.inner_product(x)
True
sage: D4embed
Lattice of degree 8 and rank 4 over Integer Ring
Basis matrix:
[1 0 0 0 0 0 0 0]
[0 1 0 0 0 0 0 0]
[0 0 1 0 0 0 0 0]
[0 0 0 1 0 0 0 0]
Inner product matrix:
[ 2 -1  0  0  0  0  0  0]
[-1  2 -1 -1  0  0  0  0]
[ 0 -1  2  0  0  0  0  0]
[ 0 -1  0  2  0  0  0  0]
[ 0  0  0  0  2  0  0  0]
[ 0  0  0  0  0  2  0  0]
[ 0  0  0  0  0  0  2  0]
[ 0  0  0  0  0  0  0  2]

The input may be a list of three or more lattices:

sage: # needs sage.graphs
sage: A7 = IntegralLattice("A7")
sage: D5 = IntegralLattice("D5")
sage: gA7 = A7.discriminant_group().gens()[0]
sage: gD5 = D5.discriminant_group().gens()[0]
sage: [L, phi] = IntegralLatticeGluing([A7, A7, D5, D5],
....:                          [[gA7, gA7, gD5, 2 * gD5],
....:                          [gA7, 7 * gA7, 2 * gD5, gD5]], True)
sage: L.determinant()
1
sage: B = phi[0].matrix()
sage: B*L.gram_matrix()*B.transpose() == A7.gram_matrix()
True

The gluing takes place in the direct sum of the respective ambient spaces:

sage: # needs sage.graphs
sage: L1 = IntegralLattice("D4", [[1, 1, 0, 0], [0, 1, 1, 0]])
sage: L2 = IntegralLattice("E6", [[0, 2, 0, 0, 0, 0], [0, 0, 0, 0, 1, 1]])
sage: [f1, f2] = L1.discriminant_group().gens()
sage: [g1, g2] = L2.discriminant_group().gens()
sage: [L, phi] = IntegralLatticeGluing([L1, L2],
....:                                  [[f1, g1], [f2, 2 * g2]], True)
sage: phi[0]
Free module morphism defined by the matrix
[ 2  2 -2 -1]
[ 0  2 -1  0]
Domain: Lattice of degree 4 and rank 2 over Integer Ring
Basis matrix:
[1 1 0 0]
[0 1 1 0]
Inner product matrix:
[ 2 -1  0  0]
[-1  2 -1 -1]
[ 0 -1  2  0]
[ 0 -1  0  2]
Codomain: Lattice of degree 10 and rank 4 over Integer Ring
Basis matrix:
[ 1/2    0 -1/2    0    0  1/2    0    0  1/2  1/2]
[   0  1/2  1/2    0    0  1/2    0    0    0    0]
[   0    0    0    0    0    1    0    0    0    0]
[   0    0    0    0    0    0    0    0    1    1]
Inner product matrix:
[ 2 -1  0  0  0  0  0  0  0  0]
[-1  2 -1 -1  0  0  0  0  0  0]
[ 0 -1  2  0  0  0  0  0  0  0]
[ 0 -1  0  2  0  0  0  0  0  0]
[ 0  0  0  0  2  0 -1  0  0  0]
[ 0  0  0  0  0  2  0 -1  0  0]
[ 0  0  0  0 -1  0  2 -1  0  0]
[ 0  0  0  0  0 -1 -1  2 -1  0]
[ 0  0  0  0  0  0  0 -1  2 -1]
[ 0  0  0  0  0  0  0  0 -1  2]
sage: B = phi[0].matrix()
sage: B * L.gram_matrix() * B.transpose() == L1.gram_matrix()
True
sage.modules.free_quadratic_module_integer_symmetric.local_modification(M, G, p, check=True)#

Return a local modification of \(M\) that matches \(G\) at \(p\).

INPUT:

  • M – a \(\ZZ_p\)-maximal lattice

  • G – the gram matrix of a lattice isomorphic to \(M\) over \(\QQ_p\)

  • p – a prime number

OUTPUT:

an integral lattice \(M'\) in the ambient space of \(M\) such that \(M\) and \(M'\) are locally equal at all completions except at \(p\) where \(M'\) is locally equivalent to the lattice with gram matrix \(G\)

EXAMPLES:

sage: # needs sage.graphs sage.libs.pari
sage: from sage.modules.free_quadratic_module_integer_symmetric import local_modification
sage: L = IntegralLattice("A3").twist(15)
sage: M = L.maximal_overlattice()
sage: for p in prime_divisors(L.determinant()):
....:     M = local_modification(M, L.gram_matrix(), p)
sage: M.genus() == L.genus()
True
sage: L = IntegralLattice("D4").twist(3*4)
sage: M = L.maximal_overlattice()
sage: local_modification(M, L.gram_matrix(), 2)
Lattice of degree 4 and rank 4 over Integer Ring
Basis matrix:
[1/3   0 2/3 2/3]
[  0 1/3   0 2/3]
[  0   0   1   0]
[  0   0   0   1]
Inner product matrix:
[ 24 -12   0   0]
[-12  24 -12 -12]
[  0 -12  24   0]
[  0 -12   0  24]